This PDF file contains the front matter associated with SPIE Proceedings Volume 6451, including the Title Page, Copyright information, Table of Contents, and the Conference Committee listing.

We review spectroscopic properties, basic laser parameters, and efficient lasing of Pr-doped fluoride materials. Continuous output powers up to 600 mW in the visible spectral range as well as intracavity frequency doubling to the UV spectral region under semiconductor laser pumping is reported. We achieved powers of 600 mW in the visible spectral region and 360 mW of UV radiation corresponding to a conversion efficiency of 61% with an optical-to-optical efficiency of 22%.

In this paper, we report on 500 mW of cw ultraviolet radiation at 360 nm, which has been obtained by intracavity frequency doubling of a Pr:YLF laser, end pumped by 1.8 W Coherent High Power OPS Laser at 479 nm. We have demonstrated the scalability of Pr:YLF laser to pump power of 5.3Watts, resulting in real continuous wave 2.5 Watts of output power at 720 nm and cw 1.3 Watts at 360 nm.

In this paper, we report on 2.5 Watts of output power at 522 nm of Pr:YLF laser end pumped by 5.3 W Coherent High Power OPS Laser at 479 nm, and on 620 mW of cw ultraviolet radiation at 261 nm, which has been obtained by intracavity frequency doubling of the Pr:YLF laser with a BBO crystal.

Low noise CW UV lasers are needed for applications in bioinstrumentation (cell sorting, cytometry...) and semiconductors (wafer inspection, micromachining ...). We have recently demonstrated that such laser sources can be obtained with diode pumped solid state (DPSS) architectures. One key to success was the quasimonolithic structure of the laser. The advantages of quasi-monolithic DPSS lasers for UV generation are simplicity of design, compactness, efficiency and thus low power requirements and limited heating. In this paper, we present for the first time a long term characterization of the diode pumped CW 355 nm laser. The interplay between pump absorption, cavity length, 1064 mode size, walk-off angle, acceptance angle has been optimized. In our experiments, the temperature of each element of the laser was controlled and UV power, noise and spectra were monitored versus these temperatures. At 2.5 W pump power, low noise UV power beyond 30 mW was measured on most samples built. At a reduced pump power of 1.65 W, all lasers were operating at 10 to 15 mW and could be maintained at 10 mW over days. The noise level remained below the 1% rms level. More long-term measurements will be presented at the conference.

Efficient frequency conversion of high-repetition-rate femtosecond pulses and high-energy picosecond pulses with wide tunability throughout the visible and ultraviolet (UV) is described in BiB₃O₆. By implementing a femotsecond optical parametric oscillator (OPO) based on BiB₃O₆, the entire visible spectrum across 480-710 nm is accessed at practical average powers of up to 270 mW in pulses of 120 fs at 76 MHz repetition rate. Internal frequency doubling of the visible OPO signal pulses in &bgr;-BaB₂O₄ has also permitted femtosecond pulse generation with wide tunability across 250-350 nm in the UV, at up to 100 mW of average power. The potential of BiB₃O₆ for frequency conversion of high-intensity pulses is also demonstrated by third harmonic generation of amplified microjoule picosecond pulses at 1064 nm. Output pulse energies of 216 &mgr;J in 29 ps duration at 25 Hz repetition-rate have been obtained at 355 nm with overall conversion efficiencies of 50%. Optical parametric generation and amplification of high-intensity picosecond pulses in the visible and UV is also reported in BiB₃O₆, providing tuning across 370-740 nm, pulse energies of 48 &mgr;J pulse durations of 18 ps, and efficiencies as high as 30%.

Compact DPSS UV sources are of interest for replacing Ar-Ion lasers in applications that require cw or quasi-cw laser radiation. One way to generate UV light at 355nm and 266nm is by modelocking an IR Nd:YVO₄ laser and converting the ps pulses into the second, third, and fourth harmonic. The mechanism of choice is passive modelocking using a Saturable Bragg Reflector (SBR). We have developed an air-cooled system capable of UV output powers in excess of 6W. Laser performance as well as lifetime data will be presented for wavelengths at 355nm and 266nm.

Optically pumped semiconductor lasers offer significant advantages with respect to all traditional diode-pumped solid state lasers (including fiber lasers) in regards to wavelength flexibility, broad pump tolerance, efficient spectral and spatial brightness conversion and high power scaling. In this talk we will describe our recent progress in the lab and applying this technology to commercial systems. Results include diversified wavelengths from 460 to 570nm, power scaling to >60W of CW 532nm, and the launch of a low cost 5W CW visible source for forensic applications.

Power-scaling of optically pumped semiconductor lasers (OPSL's) using a resonator with multiple OPS chips is demonstrated. With a 3-chip cavity and intra-cavity second harmonic generation, we obtain 55W of TEM₀₀ mode output at 532 nm and 66 W in multi-transverse mode. In addition, we describe the design of a periodic dynamically stable resonator that allows scaling to more than 4 chips and demonstrate that the output power scales with the number of chips in the cavity.

We present new approaches for power scaling and tunability in semiconductor disk lasers. The novel concepts allow for reduced thermal load of the gain material, increasing the threshold of rollover and extending the capability for boosting the output power without significant degradation in the beam quality. The proposed technique for power scaling of optically-pumped semiconductor disk lasers is based on the multiple gain scheme. The method allows for significant power improvement while preserving good beam quality. Total power of over 8 W was achieved in dual-gain configuration, while one-gain lasers could produce separately about 4 W, limited by the thermal rollover of the output characteristics. The results show that reduced thermal load to a gain element in a dual-gain cavity allows extending the range of usable pump powers boosting the laser output. Tunable Sb-based semiconductor disk laser operating at 2-&mgr;m is demonstrated with nearly 100 nm operation range. The maximum output is 210 mW and the 3dB tuning range spans from 1946 to 1997 nm. The wavelength tuning is based on an intracavity birefringent filter. The potential of semiconductor disk lasers for high repetition rate ultrashort pulse generation using harmonic mode-locking is also discussed. We report on optically-pumped vertical-external-cavity surface-emitting lasers passively mode-locked with a semiconductor saturable-absorber mirror. The potential of harmonic mode-locking in producing pulse trains at multigigahertz repetition rates has been explored. The results present first systematic study of multiple pulse formation in passively mode-locked VECSELs.

Diode pumped frequency doubled Optically Pumped Semiconductor lasers (OPS), has proven to be a reliable source of laser radiation in the blue and blue-green spectral range between 460 nm and 505 nm. One of the major advantages of using semiconductors as gain medium is the possibility to tailor the wavelength of the semiconductor material by means of band gap engineering. Here we report about new OPS material enabling the wavelength region between 1090 nm and 1160 nm which allows the realization of frequency doubled lasers between 545 nm and 580 nm. Laser results up to several Watts in the yellow spectral range as well as efficiency and lifetime data will be presented.

Pulsed lasers with high average output power in the green spectral range are of interest for laser annealing applications. In this paper an efficient pulsed diode-pumped Yb:YAG thin disk laser with intracavity frequency doubling is presented. The Yb:YAG laser crystal disk has a thickness of 180 &mgr;m and a diameter of 10 mm and is pumped by a laser diode stack at a wavelength of 938 nm. The disk is soldered to a water-cooled Cu-W heat sink and exhibits a nearly perfect spherical surface. The folded resonator is dynamically stable with a beam factor of M² = 5 and which is matched to the requirements of the application. Acousto-optical and electro-optical switches are investigated to operate the laser in the cavity-dumping mode. An average output power of 150 W at 515 nm is achieved. The diode-to-green efficiency is about 28%. A critically phase matched LBO crystal is used for intracavity second harmonic generation. We show that stable pulsing is obtained from 10 kHz to 150 kHz. The pulse-width can be varied from 200 ns to 700 ns by control of the low-loss period of the switching element. The experimental results are compared with theoretical modeling of the system and first application results are discussed.

We are presenting the outcome of the development of an external frequency doubled, pulsed thin disk Yb:YAG laser for use in the GLAS (Ground-layer Laser Adaptive-optics System) project. The special goal was a very high robustness and reliability needed for the operation at the William Herschel Telescope on La Palma. For the green output at &lgr; = 515nm we report pulse lengths down to 250ns and an average power of 23W at 3kHz repetition rate and up to 32W average power and minimum pulselengths of 350ns at 5kHz. At all power levels the beam is nearly diffraction limited with M² ⩽ 1.1.

Nd:YVO₄ is a widely used gain medium in commercial lasers providing up to several tens of watts in a diffraction limited beam. Its high gain favors high repetition rates and short pulses in nanosecond Q-switched and picosecond mode-locked regimes. However, output power is limited by strong thermo-optical effects leading to an aberrated thermal lens and ultimately the crystal's fracture. In this contribution, we present the optimized pumping of vanadate at 888 nm, benefiting from polarization-independent absorption, reduced quantum defect and very low absorption coefficients compared to the common pump wavelengths of 808 and 880 nm. After a presentation of the principle and the key characteristics of a high-power fiber-coupled end-pumped multimode oscillator, a series of systems based on this pumping technique are presented. A compact 60W high-efficiency TEM₀₀ CW oscillator first proves the potential for high-power high-beam-quality systems. A CW intracavity-doubled system provided 62 W of power at 532 nm. A cavity-dumped Q-switched oscillator providing up to 47 W of average power with 6 ns long pulses at all repetition rates was investigated. Passive mode-locking of an oscillator providing 56 W of output power was achieved with a saturable absorber mirror. Finally, a high-power oscillator was amplified with high efficiency in a power amplifier based on the same pump/crystal configuration. The wide range of systems demonstrated illustrates the simplicity and flexibility of 888 nm pumping for extending the benefits of vanadate in the higher power range.

In diode pumped Nd:YAG lasers the quantum defect is the most important parameter determining the thermal load of the laser crystal. This can be dramatically reduced by pumping directly into the upper laser level. Therefore a high power end-pumped Nd:YAG laser with direct pumping into the upper laser level will be presented. An 8 bar diode stack with central wavelength of 885 nm and a spectral width of 2.5 nm was used to pump a diffusion bonded Nd:YAG crystal with total length of 62 mm and 5 mm in diameter. With an absorbed pump power of 438 W an output power of 250 W was realized. For further power scaling a multi-segmented laser rod was used and up to 276 W of output power was achieved. Further investigations on thermal load and thermal optical effects will be presented.

A resonator setup applying a double-sided diode end-pumped configuration and an electro-optical Q-switch for efficient generation of 4 mJ pulses (< 60 ns fwhm) at 935 nm from Nd:YGG is presented, to our knowledge for the first time. The optical-optical efficiency is 9 % (absorbed pump light to laser out). High quality crystals have been investigated, showing high damage threshold, high efficiency and good optical properties permitting Q-switched mode of operation. Experimental small signal gain data coincide with spectroscopic measurements. For vapour detection frequency stable single mode operation is required. Injection seeding with a single frequency cw-signal has been successfully achieved. Frequency control mechanisms are currently under investigation. The direct generation of 935 nm radiation simplifies future LIDAR systems significantly compared to current approaches based on OPO, Raman or Ti:Sapphire technology.

For weather forecast, especially for civil protection from high-impact weather events, measuring the three-dimensional distribution of water vapour by DIAL techniques is a fundamental concern. Especially for development and evaluation of atmospheric models, knowledge of water vapour distribution is important. Suitable wavelengths for a water vapour DIAL are e.g. around 943 nm. This region can be reached with well established technologies such as the optical parametric oscillator (OPO) and the Ti:Sapphire laser. But these systems suffer from low efficiency and complex set-up. In contrast the Nd:GSAG laser presented here can be directly pumped with 808 nm laser diodes. This supports the realisation of an efficient and compact laser system. Different oscillator and amplifier setups working at 943 nm were realised. An output energy of >17 mJ in a 100 ns pulse with 10 Hz repetition rate was demonstrated. In a MOPA system a double pass gain of 1.5 and an output energy of >18 mJ was achieved. The Nd:GSAG laser oscillator was successfully injection seeded with DFB laser diode from FBH-Berlin. Also the gain cross section in a Nd:GSAG laser crystal from 941-944 nm was measured. The FWHM of the homogeneous line is 2 nm with a peak stimulated emission cross section of 4.0•10^-20 cm² at 942.7 nm.

Transition metal ions have been of great interest from the beginning of laser development because of their broadband emission. The first demonstration of a transition metal laser used Ni²⁺ as the active ion in 1963. Other transition metal ions such as Co²⁺ have also been developed as lasers but low cross sections and the need for cryogenic cooling to achieve high efficiency hindered their transition from discovery to applications. The 1995 innovation of pairing Cr²⁺ with a host that has tetrahedral symmetry substitution sites led to demonstration of broadly tunable, room temperature, mid-IR lasers. Progress in advancing this class of transition metal laser to output power of 18 W, tuning range to several hundred nanometers, and modelocked operation down to 100 fsec will be reviewed. Plans for future development in the areas of femtosecond pulse operation, high speed frequency tuning, fiber format, and direct electronic pumping will be discussed.

The use of Fe:ZnSe polycrystals as passive Q-switches for the Er:Cr:YSGG laser operating at 2.8&mgr;m is introduced. Fe:ZnSe samples with 1-7cm^-1 coefficients of absorption were prepared using thermal diffusion of iron in CVD grown polycrystalline ZnSe. A flashlamp pumped Er:Cr:YSGG laser with a variable (40 - 80% reflectivity) output coupler (OC) was used as a test bed for passive Q-switching. Using a 90% initial transmission Fe:ZnSe placed at the Brewster angle we obtained a single giant pulse lasing with a pulse duration of ~65 ns and a maximum output of 13 mJ under 30 J of flashlamp pump. Multi-pulse (19 pulses) output was obtained with 85 mJ total output energy at a pump energy of 30 J. The saturation curve of Fe:ZnSe was measured. Fitting this data with a theoretical model results in absorption crosssection of 0.56 × 10^-18 cm², which is close to the value of the absorption cross-section obtained from spectroscopic measurements (0.85 × 10-18 cm² at 2.8 &mgr;m).

Cr:ZnSe crystals grown by the Bridgeman technique from the melt in inert gas (argon) under pressure were characterized and utilized as effective laser active material. Large crystalline boules with a necessary concentration of Cr²⁺ ions 10¹⁹ cm^-3, practically homogeneously distributed throughout the crystal bulk (50 mm in diameter and up to 100 mm in length), were prepared. For the laser evaluation the Cr:ZnSe samples in the form of 6 mm thick blocks were polished. Cr:ZnSe laser was longitudinally coherently pumped either with flashlamp-pumped Er:YAP laser radiation (emission wavelength 1658 nm) or with diode-pumped Tm:YAP laser radiation (emission wavelength 1980 nm). In the first case, the Cr:ZnSe laser was pumped with radiation of Er:YAP laser working in free-running regime (pulse length 200 &mgr;s, pulse energy 200 mJ, repetition rate 1 Hz). The maximal obtained Cr:ZnSe laser pulse energy was 14 mJ (slope-efficiency 73%). Using the dispersive prism inside the resonator, the output laser radiation was broadly tunable from 2150 nm up to 2600 nm. In the second case, the Cr:ZnSe laser was pumped with radiation of diode-pumped solid-state Tm:YAP laser working in pulsed as well as continuous-wave regime, for which the maximal obtained Cr:ZnSe laser output power was 200 mW (slope-efficiency 67%). The output spectrum of generated radiation covered the range from 2100 nm to 2400 nm. The temporal profile and spatial structure of laser beam were measured. The Cr:ZnSe crystal grown by the Bridgeman method was demonstrated as an efficient broadly tunable laser active material generated radiation in the mid-infrared spectrum and operated in room-temperature.

PbWO₄ crystals with Ho concentration ranging from 0.2% to 4% were grown by the Czochralski method. Polarized optical absorption, emission and kinetics of fluorescence were studied over 20-300K temperature and 0.2-8&mgr;m spectral ranges. Stimulated Raman scattering in PbWO₄ crystal was studied under 1.6 and 2.0 &mgr;m excitation.

Significant performance improvement of the Er(0.5%):YAG diode pumped solid state laser (DPSSL) has been achieved by pump diode spectral narrowing via implementation of external volumetric Bragg grating (VBG). Without spectral narrowing, with a pump path length of 15 mm, only 37% of 1532 nm pump was absorbed. After the VBG spectral narrowing, the absorption of the pumping radiation increased to 62%. As a result, the incident power threshold was reduced by a factor of 2.5; the efficiency increased by a factor of 1.7, resulting in a slope efficiency of ~23%. A maximum of 51 W of CW power was obtained versus 31 W without the pump spectrum narrowing.

Room temperature, multi-wavelength operation in 2% doped Er:YAlO₃ under flashlamp excitation is reported. Lasing occurred predominantly at 1.6625 &mgr;m and 1.6725 &mgr;m with the emission at the two wavelengths being orthogonally polarized. The use and orientation of an intracavity polarizer dictates the lasing wavelength in the laser. Temporal analysis of the two laser wavelengths shows that the onset of lasing at the two wavelengths is separated by ~14 &mgr;s with lasing at the 1.6625 &mgr;m wavelength occurring first. The 14 &mgr;s delay suggests that the 1.6625 &mgr;m emission is due to lasing on the ⁴S_3/2 →⁴I_9/2 transition (4-level), while the 1.6725 &mgr;m emission is due to cascaded lasing on the ⁴I_13/2 →⁴I_15/2 transition (3-level). Using a rotating mirror Q-switch, ~80 ns pulses at 10 mJ/pulse were generated. The wavelength of the Q-switched emission was determined to be at 1.6625 &mgr;m.

For many applications, like micromanufacturing, remote sensing, data storage, etc. a microchip Nd:YAG laser is suitable. From the measurement of the laser radiation transmission through the eye tissue is evident that the injury probability of the retina is higher for the case of 1064 nm instead of 1338 nm. The main reason for that is the radiation water absorption. The Q-switched diode pumped (at 808 nm) microchip laser emitting radiation at wavelength 1338 nm was designed and realized. This laser was based on diffusion bonded crystal (diameter 5 mm) which combines in one piece the laser active part (Nd:YAG, 4 mm long) and saturable absorber (V:YAG, 0.7 mm, T₀ = 85%). The microchip resonator mirrors were deposited directly on the bonded crystal surfaces, output coupler reflexivity was 90%. The constructed "alignment-free" Q-switched microchip laser was tested under pulsed, and CW diode pumping. In both cases, the generated pulse energy, pulse length, emission wavelength, polarization, and laser beam profile were measured. The energy up to 18.6 &mgr;J in 1.7 ns long pulses was reached at the wavelength 1338 nm. TEM₀₀ laser mode was linearly polarized. The interaction of the radiation from the near- and mid-infrared region with the eye tissue was investigated and as conclusion the microchip with the wavelength 1338 nm was chosen as a good compromise between the eye safe 1.5 &mgr;m radiation and commonly, in the application used, 1.06 &mgr;m radiation.

We present a long term stable single frequency MOPA with 40 W output power and M² < 1.2 consisting of an ultrastable 1 W non-planar ring cavity oscillator with outstanding single frequency characteristics and one Innoslab amplifier stage. The partially end pumped Nd:YVO4 Innoslab amplifier is set up in a folded single pass configuration. A 30 GHz tunable spectral bandwidth of 1kHz/100ms and a relative intensity noise (RIN) of < 1 10^-5 Hz^-1/2 (>10kHz) was measured in free-running mode. Together with an active intensity noise suppression electronics a RIN of < 5 10^-7 Hz^-1/2 (>10kHz) was achieved. A comprehensive discussion of experimental data is given.

A frequency-tripled nanosecond pulsed Ti:sapphire laser injection-seeded by a cw single-frequency Ti:sapphire laser has been developed. The single-frequency stability of this light source is demonstrated successfully by matching between the optical frequency of the seed laser and the cavity frequency of the slave laser with build-up time electronics. It is also discussed with fluctuations of the wavelength of the Ti:sapphire laser and the optogalvanic signal of silicon atoms. This unique light source opens the door to silicon atom optics, which is capable of manipulating atoms isotopically for novel material processing.

Cryogenic cooling of Ti:Sapphire is a well known technique for improving its thermal performance. In particular the improvement in thermal conductivity, temperature dependence of the index of refraction and thermal expansion around 77 K dramatically reduces the thermal lensing. This allows a significant increase in the possible pump power, while keeping a very good beam quality over a wider range of operation. As an example we demonstrate a single-stage regenerative amplifier that is capable of delivering compressed output powers of 7.5 W and 11.9 W at 1 and 5 kHz, respectively, as well as a multi-pass amplifier delivering 13.2 W at 1 kHz.

We describe a 60W, 70fs, 20kHz Ti:sapphire CPA laser system using cryogenically-cooled amplifiers, currently operating at the Advanced Light Source at LBNL. The system consists of an oscillator, a 20 kHz regenerative preamplifier, and two power amplifiers to produce two output beams, each at 30W. Each power amp can be pumped by two 90 Watt, 10 kHz, diode-pumped, doubled YLF lasers simultaneously (for 10 kHz) or interleaved in time (for 20 kHz). The regen is pumped at 20 kHz and 60W, producing 8W output which is split between the power amps. To maintain the crystals near the thermal conductivity peak at ~50°K, we used 300 Watt cryorefrigerators mechanically decoupled from the optical table. Pulses are compressed in a quartz transmission grating compressor, to minimize thermal distortions of the phase front typical of gold coated gratings at high power density. Transmission through the compressor is >80%, using a single 100 x 100mm grating. One of the 30W output beams is used to produce 70fs electron bunches in the synchrotron light source. The other is delayed by 300ns in a 12-pass Herriot cell before amplification, to be synchronized with the short light pulse from the synchrotron.

Using a side-pumping geometry, we obtained 400 W of cw power with 56% optical-to-optical efficiency from a cryogenically-cooled, Yb:YAG laser. In Q-switched operation, we obtained 200 W with a near diffraction limited beam.

In this paper we discuss a CW Yb:YAG cryogenic laser program that has resulted in the design and demonstration of a novel high power laser. Cryogenically-cooled crystalline solid-state lasers, and Yb:YAG lasers in particular, are attractive sources of scalable CW output power with very high wallplug efficiency and excellent beam-quality that is independent of the output power. This laser consists of a distributed array of seven highly-doped thin Yb:YAG-sapphire disks in a folded multiple-Z resonator. Individual disks are pumped from opposite sides using fiber-coupled ~ 30W 940nm pump diodes. The laser system we have constructed produces a near-diffraction-limited TEM₀₀ output beam with the aid of an active conduction-cooling design. In addition, the device can be scaled to very high average power in a MOPA configuration, by increasing the number and diameter of the thin disks, and by increasing the power of the pump diodes with only minor modifications to the current design. The thermal and optical benefits of cryogenically-cooled solid-state lasers will be reviewed, scalability of our Yb:YAG cryogenic laser design will be discussed, and we will present experimental results including output power, slope and optical-optical efficiencies, and beam-quality.

Advances in the output powers and beam quality of DPSS lasers have provided tens of Watts of green pump power in a reliable and compact form. This paper describes advances in the performance of both single frequency CW and femtosecond modelocked Ti:Sapphire (Ti:S) lasers using such high power pump lasers. Short wavelength performance below 660 nm for the CW system is described and long wavelength tunability beyond 1100 nm. Continuous tunability of the modelocked system of over 400 nm will be presented and power performance for different output coupling and pump levels described. The applicability of these high performance systems to demanding new applications will also be described.

A novel device designed for pulse shaping, characterization and phase compensation in ultrafast laser systems is described. The pulse shaper exhibits low transmission loss and is widely applicable to lasers with spectral bandwidth from 10 nm to over 400 nm. Pulse characterization and phase compensation is fully computer controlled in a closed loop via MIIPS method. This system is designed to enhance performance of ultrafast oscillators and ultrafast amplifiers including terawatt lasers and cryogenically cooled amplifier systems. Seed laser spectral amplitude shaping results in increased bandwidth while preserving the output power in ultrafast regenerative amplifiers. Subsequent phase compensation enables the robust delivery of output pulses within couple of percent of transform limit. Such system could find numerous applications including MPE microscopy, CARS, and more general coherent control experiments.

We demonstrate operation of a simple and reliable water-cooled femtosecond laser running at 10 kHz suitable for industrial micromachining applications. A laser geometry involving only a regenerative amplifier and delivering 3.5 W average power 60-fs pulses is compared to a more conventional architecture using an additional multi-pass amplifier. Both laser systems require a moderate pumping laser of ~30 W average power and deliver high-quality beams (M²<1.2). PACS : 42.55-f ; 42.60 v; 42.60 Rn

We report here the development and construction of a two-flashlamp pumping cavity for a Cr:LiSAF rod, to be operated as a multipass amplifier in a Chirped Pulse Amplifier system. The pumping cavity was designed to minimize the thermal load on the gain medium by the utilization of intracavity filters, aiming operation with high gain and the highest possible repetition rate. Operating as a laser, 30 Hz repetition rate and 20 W average power were obtained for the first time at a maximum gain per pass of 1.5. Changing the pumping characteristics, the laser provided 16 W at 8 Hz repetition rate, at a maximum gain of 3.6. A four-pass multipass amplifier geometry was designed for the pumping cavity, that was integrated and synchronized to a Ti:Sapphire Chirped Pulse Amplifier system. The amplification properties of the gain medium were determined, in one, two and four passes, along with the gain dependence on the repetition rate. The amplifier final configuration provided amplification by a factor 150 to 20 ps stretched pulses, resulting in final compressed pulses with 60 fs and 0.5 TW of peak power at 5 Hz repetition rate.

We discuss a new method to shape the temporal response of saturable absorption in semiconductors. In particular, we investigate the possibility to control independently the absorption recovery time of each quantum-well forming the semiconductor absorber. The recovery time is tailored by irradiation with nitrogen ions produced by an RF-plasma source. The irradiation is performed in-situ as one step of the epitaxial growth process; the quantum-wells are individually exposed to a flux of N-ions after they are grown. The amount of non-radiative recombination centers within the quantum-wells is strongly related to the time interval during which the N-ions flux is active and to the thickness of the semiconductor layer grown on top of each quantum-well before the irradiation is performed. We apply this method to fabricate fast semiconductor saturable absorbers operating in the 1-&mgr;m wavelength range. The absorption recovery time could be changed from 300 ps to 10 ps without degradation of the nonlinear optical response. The practicality of the design is finally proved by using the semiconductor saturable absorbers for mode-locking Yb-doped fiber lasers.

The optical properties of Yb:YAG ceramic doped with different Yb concentrations are presented. The absorption coefficient at peak absorption wavelength of 940 nm increases linearly with Yb concentration in Yb:YAG ceramics. Low-threshold and highly-efficient continuous-wave (cw) laser-diode end-pumped Yb:YAG microchip ceramic laser with near-diffraction-limited beam quality was demonstrated at room temperature. Slope efficiencies of 79%, 67% and optical-to-optical efficiency of 60%, 53% at 1030 nm and 1049 nm, respectively were achieved for 1-mm-thick Yb:YAG ceramic plate (C_Yb = 9.8 at.%) under cw laser-diode pumping. Dual-wavelength operation at 1030 nm and 1049 nm with 5% transmission of the output coupler was achieved by varying pump power intensity. 1049 nm laser operation was automatically obtained by using 5% transmission output coupler when absorbed pump power is higher than 1 W. The lasers operate in multi-longitudinal-mode; the effect of pump power on the laser emission spectra for both wavelengths is addressed. The laser wavelength around 1030 nm shifts to short wavelength at low pump power region and then to red with increase of the absorbed pump power, while the laser wavelength around 1049 nm does not change with the pump power. Excellent laser performance indicates Yb:YAG ceramic laser materials could be potentially used in high-power solid-state lasers operating at 1030 nm, 1049 nm, or both wavelengths simultaneously. Laser-diode pumped lowthreshold and highly-efficient passively Q-switched Yb:YAG ceramic microchip laser with Cr⁴⁺:YAG ceramic as saturable absorber has also been demonstrated. The slope efficiency is as high as 37%, and the optical-to-optical efficiency is as high as 29% for 89% initial transmission of Cr⁴⁺:YAG ceramic. The pulse width of 380 ps and peak power of over 82 kW at repetition rate of 12.4 kHz was obtained. Single-longitudinal-mode oscillation and wide-separated multi-longitudinal-mode oscillation due to etalon effect of Cr⁴⁺:YAG thin plate was achieved depending on the pump power level.

With recently developed diode-lasers to resonantly pump solid-state crystalline lasers, new opportunities arise for systems such as Tb³⁺ as an activator ion in different host matrices. For example the observed fluorescence from ⁵D₄→ ⁷F₅ transition (540 to 560 nm) of Tb³⁺ in TbAlO₃ represents such a possibility. There is little fluorescence quenching in this crystal involving this transition, and the measured lifetime is approximately 2 ms, long enough to sustain sufficient population for stimulated emission. The quantum efficiency is better than 50 % as measured in this material. For this same transition, others have reported room-temperature pulsed laser operation at 544 nm for Tb:YLF, where the lifetime is comparable. Mid- and long wavelength infrared laser emission has been observed for Tb³⁺ in chalcogenide glass fibers that complement our spectroscopic findings for Tb³⁺ in pedestal-grown Y₂O₃ and YAG fibers. We have identified the infrared transitions that may lase at transitions between different manifolds within the ⁷F_J multiplet. In the present study we first evaluate the various visible and infrared experimental findings with a Judd-Ofelt analysis of Tb³⁺ in TbAlO₃. We predict a radiative lifetime of 3.5 ms for the excited ⁵D₄ manifold to the ⁷F_J manifolds with more than 50% of the emission represented by the ⁵D₄→ ⁷F₅ transition. To account for the visible stimulated emission, we report transition probabilities for ⁵D₄→ ⁷F_J transitions and for diode-pumped infrared transitions we report similar spectroscopic properties for transitions within the ⁷F_J multiplet.

We studied several crystals of Yb-doped LuVO₄ with different orientations (a-cut and c-cut) in order to evaluate the potential of this new laser material for high power continuous-wave operation using simple hemispherical cavities, longitudinally pumped by a fiber coupled diode laser. We achieved substantial improvement with respect to previous results in terms of output power and slope efficiency. The highest output power and optical efficiency were obtained for the &pgr;-polarization using a-cut samples. Bistability of the input-output power characteristics in terms of a hysteresis loop was also observed. Significant intensity fluctuations were found existing in a small operational region near the critical point (up-threshold) of the bistability region. The heating of the crystal is reduced in the lasing state when stimulated emission keeps the part of the radiative relaxation high in comparison to the nonradiative relaxation processes.

The usual method to determine the ablation threshold of solid samples by ultrashort laser pulses is done by focusing the laser beam on the samples surface by a known lens, requires the knowledge of all the geometrical parameters (lens focus, beam propagation parameters, beam quality, sample position), and a series of measurements for different pulse energies. We present here a simpler method for determining ultrashort laser pulses ablation threshold for solid samples. The method uses a focusing lens, and requires only the knowledge of the pulse power, employing a diagonal translation of the sample through the laser beam waist, resulting in a pattern etched on the sample surface. The ablation threshold value is obtained measuring only one dimension of this pattern and a straightforward mathematical relation, There is no need to know any other geometrical parameter of the laser beam or of the lens used. The technique was employed to determine the ablation threshold of pure and Cr doped LiSAF samples for 20 picoseconds pulses, and a dependence with the Cr concentration was observed.

We present the results of an investigation of the spectroscopic properties of Ce³⁺:BaY₂F₈ (BYF), which is a potential laser material with an emission wavelength range from 320 nm to 360 nm. We have employed a time-resolved pump-probe technique to investigate the polarization-dependent absorption and emission properties, and the dynamic color centre formation process. We observe strong absorption from colour centres with millisecond and second lifetimes that will certainly prevent laser action with the crystals used here. Evidence suggests that there may be potential gain in this crystal if long-lived colour centres can be reduced.

A measurement station to examine the longitudinal mode structure of Q-switched solid state lasers on a single pulse basis is presented. The key component is a Fabry-Perot interferometer (FPI) providing a high finesse to not only display the full spectral emission bandwidth but also resolve single modes of high gain laser media such as Nd : YVO₄. In addition the setup allows one to link relative pulse energy data to each recorded fringe pattern. It is then used to quantify the spectral information of three lasers with a cavity length of up to 200mm to evaluate correlations among pulse stability, pulse repetition frequency and spectral emission characteristics. The optical approach implies a decaying finesse from approximately 250 to 60 across the measurement range. Therefore the setup can only partially resolve single longitudinal modes of lasers with a cavity length greater than 130mm but still gives a qualitative picture of the emission bandwidth that allows a deeper understanding of the spectral characteristics and thus points the direction for performance improvement.

The Hollow Metallic Winglets / HMW-THS, a turbo engine optimised for cooling electronics, handles large flows of energy, gas and air. Its heat exchanging shell, of huge area, tops the pressurised Can; the bottom fits a window. The hosted machine is built around a large inner gas distributor which integrates the main athermal structures. Considering the power levels, the ducting ease of both outer air-flows is as important and cuts noise. Two banks of hybrid mounted Laser Diodes / LDs, side or end feed each lasing Z-slab, thin and exposed to the cooling gas, which flows fast on both sides. The least path to reach the cooling gas minimises dT; to further reduce the thermal lensing effects, the local cooling can be tailored / spoiled to copy the heating density. The simplest optical etc layout is preferable but the current schemes and materials seem suitable; if required, the slab ends etc can be Brewster cut etc. The pumping section can sport a MOPA configuration to eases this function exploiting coherence. The inner pressure can be relevat but affects mildly only the outer window. Compactness and more degrees of symmetry lead to a natural athermal behaviour; the inner structure includes gas ducts dedicated to equalize its temperature. The neuter, clean He sports a top C_P and flows easily; speed and pressure increase the heat removal rate and reduce dT; the fast cycle can be important. H₂ would spoil the HT / HR coatings and the electronics and generates water. Note that He was used to cool the largest AC generators. To improve the heat removal from hot spots or weak elements, a Thermo Electric cooler can yield local, sub-ambient temperature flows. A cycle including dedicated turbo stages, intercoolers and gas expansion suits larger critical sections.

We have compared two solid-state saturable absorbers for Q-switching of longitudinally diode-pumped Nd:YAG laser operating at wavelength 1444 nm: vanadium doped garnet (V³⁺:Y₃Al₂O₅, V:YAG), and cobalt doped spinel (Co²⁺:MgAl₂O₄, Co:MALO). V:YAG crystal with initial transmission 91% was 2.2mm thick. Co:MALO crystal with initial transmission 91% was 2.0mm thick. Q-switched laser consisted of the Nd:YAG composite rod (8mm long Nd-doped part, 4mm long undoped YAG part) and the saturable absorber placed in 80mm long hemispheric cavity. As an output coupler was used concave mirror (r = 150mm) with reflectivity 98% on lasing wavelength. Giant pulses were obtained with both passive Q-switches. When V:YAG saturable absorber was used, 55 ns long (FWHM) pulses were generated with peak power 0.47kW (pulse energy 26 &mgr;J). Using Co:MALO, more powerful pulses were obtained (40 ns long, 1.0kW peak power, 45 &mgr;J energy). Advantage of less efficient V:YAG consist in possibility of diffusion bonding between Q-switch and laser active medium which allows to prepare miniature compact laser device. This concept was demonstrated by using of Nd:YAG/V:YAG monolith crystal (4mm long undoped YAG part, 8mm long Nd:YAG part, 0.5mm long V:YAG part - initial transmission 97% @ 1444 nm). This monolithic crystal, originally designed for 1338nm lasing, was placed into 23mm long cavity resonating at wavelength 1444 nm. For output coupler reflectivity 96% pulses 39 ns long with peak power 0.64kW were generated at wavelength 1444 nm.

TRUMPF Laser has developed an advanced solid-state q-switched laser, designed specifically to meet the requirements of industrial micro-processing. Pulse energies exceeding 4 mJ, pulse durations adapted to the application and a diffraction limited beam (M² < 1.2) are essential for micro-machining. A novel feature of the laser ensures its particularly high performance and overall stability. The technical concept is based on a power oscillator, where the output power is not set by adjusting the pump power, but rather by precise switching and attenuation of the pulses outside of the resonator. This leads to a high stability and a fixed concentric beam profile, independent of the actual output power of the system. In the field of micro-processing, laser light is primarily used for the precise ablation of various materials. High intensities beyond 10¹¹ W/cm² enable the development of new laser processing strategies, e.g. sublimation-cutting and -drilling. High stability in terms of beam quality, beam location (pointing stability < 10 &mgr;rad) and pulse energy allows for both the improvement of well known laser processes as well as pushing forward new applications. Additionally, the repetition rate of up to several hundred kilohertz and the high average power emphasizes the high performance of the developed system, particularly with regard to the competition with alternative manufacturing strategies. Further potential to increase the precision and to minimize the heat affected zone (HAZ) is given by the application of ultrashort picosecond and femtosecond pulses. TRUMPF Laser has already demonstrated a CPA-free, diode-pumped all-solid-state laser, delivering picosecond pulses with an average power of 50 W.

We report on recent advances in laser processing of solar cells, flexible printed circuit boards, integrated circuit packages, and semiconductor memory in the nanosecond pulsewidth regime. These process advances are enabled by innovations in lasers and continue to drive requirements for emerging pulsed solid state and fiber lasers. Demand for increased throughput is projected to push the pulse repetition frequency for pulsed solid state sources utilized in many of these applications past 100 KHz. Ongoing device miniaturization continues to enable new applications for visible and ultraviolet pulsed laser processes, particularly for semiconductor devices. This paper summarizes the current status of these select laser processes, the laser sources that power them, and the outlook for future innovations in the field.

Lidar Systems for the measurement of three-dimensional wind or cloud and aerosol formations in the earth atmosphere require highly stable pulsed single frequency laser systems with a narrow line width. The lasers for ESAs ADM-Aeolus and EarthCARE missions require frequency stabilities of 4 and 10 MHz rms at a wavelength of 355 nm and a line width below 50 MHz at 30 ns pulse duration[1]. Transferred to the fundamental wavelength of the laser systems the stability requirement is 1.3 and 3.3 MHz, respectively. In comparison to ground based lidar systems the vibrational load on the laser system is much higher in airborne and spaceborne systems, especially at high frequencies of some hundred Hertz or even some kHz. Suitable frequency stabilisation methods have therefore to be able to suppress these vibrations sufficiently. The often used Pulse-Build-up method is not suitable, due to its very limited capability to suppress vibration frequencies of the order of the pulse repetition frequency. In this study the performance of three frequency stabilisation methods in principle capable to meet the requirements, the cavity dither method, the modified Pound-Drever-Hall method and a modified Ramp-Fire method - named Ramp-Delay- Fire - is theoretically and experimentally investigated and compared. The investigation is performed on highly efficient, passively cooled, diode end-pumped q-switched Nd:YAG oscillators, which are breadboard versions of the A2D (ADM-Aeolus) and possible ATLAS (EarthCARE) oscillators. They deliver diffraction limited output pulses with up to 12 mJ pulse energy at a pulse duration of 30 ns and 100 Hz pulse repetition rate.

The National Ignition Facility (NIF) is currently the largest and most energetic laser system in the world. The main amplifiers are driven by the Injection Laser System comprised of the master oscillators, optical preamplifiers, temporal pulse shaping and spatial beam formatting elements and injection diagnostics. Starting with two fiber oscillators separated by up to a few angstroms, the pulse is phase modulated to suppress SBS and enhance spatial smoothing, amplified, split into 48 individual fibers, and then temporally shaped by an arbitrary waveform generator. Residual amplitude modulation induced in the preamplifiers from the phase modulation is also pre-compensated in the fiber portion of the system before it is injected into the 48 pre-amplifier modules (PAMs). Each of the PAMs amplifies the light from the 1 nJ fiber injection up to the multi-joule level in two stages. Between the two stages the pre-pulse is suppressed by 60 dB and the beam is spatially formatted to a square aperture with pre-compensation for the nonuniform gain profile of the main laser. The input sensor package is used to align the output of each PAM to the main laser and acquire energy, power, and spatial profiles for all shots. The beam transport sections split the beam from each PAM into four main laser beams (with optical isolation) forming the 192 beams of the NIF. Optical, electrical, and mechanical design considerations for long term reliability and availability will be discussed. Work performed under the auspices of the U. S. Department of Energy under contract W-7405-Eng-48.

The first theory for two novel coherent beam combination architectures that are the first electronic beam combination architectures that completely eliminate the need for a separate reference beam are presented. Experimental results demonstrating the coherent addition of a 3 by 3 array of fiber amplifiers with a total phase locked power of 100-W are also described.

Laser technology has developed rapidly in the last few years; efficient laser action is critical to the success of many systems designed for use in the civil and military sectors. The military operational use of laser technology has been responsible for a lot of dramatic improvements in operational performance of many weapon systems, a common example in enhanced guidance accuracy. The operational efficiency, and reduced size of modern solid-state laser technology, makes it an ideal source for many countermeasure applications; however, the ultimate performance of any system is governed by the effective integration of the various sub-systems, as the critical performance parameter is "useful energy on target". This paper concentrates on the potential application of laser devices to countermeasure systems and considers the current status of the performance of laser technology and its use in these systems. This review outlines approaches to defining laser-based system requirements, so that the laser device is compatible with the whole system and thus making optimum use of the laser energy.

We present the thermal vacuum (TVAC) test results of the engineering model laser transmitter for the NASA Lunar Orbiter Laser Altimeter (LOLA) instrument.

We present the design of the Lunar Orbiter Laser Altimeter laser transmitter which consists of two oscillators on a single bench, each capable of providing one billion shots.

Five types of passive Q-switched as well as simultaneously Q-switch mode-locked modulators: plastic dye sheets ( Kodak 9850 cellulose acetate dye sheets), lithium fluoride crystals containing F₂ ^- color centers ( LiF: F₂ ^-), chromium doped yttrium aluminum garnet crystals ( Cr⁴⁺:YAG), ionic color filter glass ( Schott RG1000 color filter glass) and the single crystal semiconductor wafers ( GaAs, Fe doped InP, Zn doped InP, S doped InP, etc.) used for the modulation of the Nd:hosted(Nd:YAG, Nd:YVO₄, and Nd:LSB) lasers have been investigated in detail in our researches. We have also investigated into the applications of the Q-switch mode-locked pulses train for the development of higher resolution solid state laser range finder. We will also present the high accuracy laser ranging results, the micro-motor that driven mechanical parts from the stepping digital ranging readout, to precisely control the best focus of a miniature zoom lens modular. The core simultaneously Q-switch mode-locked modulators microchip laser is the key part of our automatic optical inspection system.

Presented is a new combined CW Ti:Sapphire/Dye laser with horizontal output polarisation from a ring cavity and with improved stability of output frequency. Short-term output line width does not exceed 10 kHz for the Ti:Sapphire laser and amounts to 50 kHz for the Dye laser, output frequency drift being less than 30 MHz/hour, smooth scanning range is more than 19 GHz (Ti:Sapphire) and > 25 GHz (Dye). The maximum output power with a 10-W pump exceeds 2 W for the Ti:Sapphire configuration and is > 1.6 W for the dye one. The short-term line width without the frequency stabilisation is less than 5 MHz (Ti:Sapphire) and < 10 MHz (Dye); smooth scanning range without the frequency stabilisation is more than 47 GHz (Ti:Sapphire) and > 50 GHz (Dye). The total working spectral range of the combined laser stretches from 550 to 1000 nm (550-770 nm for the Dye and 695-1000 nm for Ti:Sapphire) when pumped with 532/515-nm radiation.

Lidar is an important equipment for the accurate detection of underwater targets. In this paper, a compact and remote-controlled lidar system is described. The system contains four modules which are Q-switch Nd:YAG pulse laser module, photoelectric detector module, data collector module and remote-controlled module. All of the modules are put into a hermetic container. The lidar system can be in operation under the water and carried by an underwater carrier such as ROV (Remotely Operated Vehicle). The operator controls the lidar and downloads the data from the system through a fiber. The system can automatically eliminate the return signal due to the surface wave. The system has been used in underwater bubble detection. A brief description of the lidar system and its operation is present in the paper. The experimental results of underwater bubble measurement are discussed.

For a diode end-pumped solid state laser, the pump beam is described as a Gaussian profile initially and then as a flat-top profile. In fact, the fiber-coupled pump beam is more accurately fit by a super-Gaussian beam. With the same beam waist, different beam profiles can be obtained with different m. It is a Gaussian profile if m = 1; and it is a flat-top profile if m is infinite. The super-Gaussian beam should be normalized before it is used to characterize the thermal and optical properties of a solid state laser. With this normalized super-Gaussian pump beam, the corresponding analysis on thermal temperature, thermal radial and tangential stresses, refractive index changes, OPD, birefringence, depolarization loss, and rate equations are modeled more accurately. At the meantime, as the progress of diode laser technology, powerful and narrow line width diodes are becoming available. It is possible to directly pump nonlinear crystals such as KTP, LBO for second harmonic generation using diode laser. Nonlinear conversion efficiency is discussed. Thermal properties for a super-Gaussian beam (with different m) on nonlinear crystal are analyzed using finite element analysis.