Phosphate glasses are attractive laser oscillator/amplifier materials because unlike fluoride, silicate, and other laser glass materials it combines attractive properties such as good chemical durability, ion-exchangeability, high gain, low concentration quenching, and low upconversion losses. Phosphate glasses also exhibit very high solubility for rare earth ions. This feature permits the introduction of large concentrations of active ions into relatively small volumes resulting in smaller laser devices with high-energy storage capabilities. These high dopant concentrations also result in very rapid and efficient energy transfer between rare earth ions. This allows for the effective use of Yb³⁺ as a sensitizer for the Er³⁺ laser ion. Effective Er:Yb:Glass pumping, energy storage, and energy extraction involves the population of the ²F_5/2 level of Yb³⁺ (~2ms fluorescence lifetime) and transferring energy to the ⁴I_11/2 level of Er³⁺ (~500μsec transfer time); and a very rapid (< 1μsec) nonradiative decay of the Er³⁺ from the ⁴I_11/2 state (with an 8ms fluorescence lifetime). In this study we measured the fluorescence lifetime for the ⁴I_13/2 level of Er⁺³ on different glass samples with various concentrations of erbium. The data indicates that for doping levels up to 7% (wt.%) Er₂O₃ the lifetime remains above 7.0ms. Theoretically, this highly doped glass may produce greater than 20dB gain in 1cm path length. In additional fluorescence lifetime testing, ytterbium doped and erbium/ytterbium co-doped glasses samples were evaluated for concentration quenching and energy transfer rate as function of the Er³⁺ concentration rates. The effect on teh energy transfer efficiency and laser efficiency was analyzed.

A thin two-side polished silicon etalon is demonstrated as a fixed-wavelength intracavity selector for the far-infrared p-Ge laser. The active cavity finesse is ~ 0.1. The wavelength position and spectral purity are maintained over a wide range of laser operating fields. A p-Ge laser with such a selector may find application in chemical sensing, THz imaging, or non-destructive testing.

For two meso-substituted benzo-fused pyrromethenes (BPMM and F-BPMM), photophysical and lasing properties in liquids and in poly(methyl methacrylate) (PMMA) are reported. Both dyes exhibit high quantum efficiency (0.6-0.9) along with high extinction coefficients, values which are superior to other NIR dyes such as oxazine 1 and rhodamine 800. Lasing efficiencies in the range of 20-30 % have been recorded for the new dyes. Additionally, the dyes can be pumped by a diode or dye laser emitting at 650 nm. Under continuous UV-Vis irradiation, BPMM and F-BPMM demonstrated improved photostability as compared with a previously reported analog, PM-700 (Scheme 1). The survivability of dyes under conditions of radical polymerization has also been investigated.

Direct diode-pumping of dye-based gain media has the potential to produce a very efficient, inexpensive, compact, tunable laser source. The pulsed diode lasers available for exciting dyes, however, have relatively low peak powers (up to a few watts). Therefore, the focusing characteristics of the diode beam are a key factor in reaching dye-laser threshold. In this work, detailed characterization of the output from a single-stripe red diode was done, including input/output characteristics and temporal and spatial profiles. Based on these results, transfer optics were designed to couple the diode beam into the dye-based gain medium with a small spot size. A solid-state dye element was then excited longitudinally in a low-threshold resonator. Laser results are reported, including measurements of threshold, input/output characteristics, temporal profiles, and spectral properties. The data are discussed in detail, and strategies for improving dye-laser performance are identified.

The growing interest on Yb-doped lasers has been underlined by creating new active materials with Yb³⁺ as a dopant. The anisotropic monoclinic tungstate crystals KY(WO₄)₂ and KGd(WO₄)₂ used as hosts for Yb³⁺ provide larger absorption and emission cross sections and smaller quantum defect than YAG. Especially for the thin disk laser concept highly doped materials with short absorption lengths are appropriate. We present continuous-wave (cw) lasing results with a 100% Yb-doped KYb(WO₄)₂ (KYbW), the first stoichiometric cw laser based on Yb³⁺ as an active ion. The cw laser experiments were performed with a 125-μm-thin KYbW sample. The one side high-reflective-coated KYbW crystal was positioned at one end of a V-type laser activity and fixed on a new type of a holder, a "laminar laser mount", which enable direct water cooling of the pumped region of the laser crystal. A home made cw Ti:Sappphire laser served as the pump source. CW laser oscillation was observed at a pump threshold (λ_pump=1025nm) of 70 mW with a slope efficiency of 21% with respect to the absorbed pump power at room temperature. The maximum output power amounted to 20 mW for a 0.3% outcoupling transmission. The emission spectrum was centered at λ_L=1068 nm.

This work describes recent progress in the development of solid-state laser using a composite disk the active mirror configuration. Pump diode arrays are placed around the perimeter of the disk and pump light is injected into the undoped edge. Uniform laser gain can be achieved with proper choice of lasant doping level, diode placement, and diode divergence. Effective reduction of thermo-optical distortions makes this laser suitable for pulse amplification at high-average power.

Laser beams with high peak power and narrow line output are fundamental for non-linear conversion. Novel intracavity techniques which improve the spectral brightness of a high average power, degenerate, periodically-poled Lithium Niobate (PPLN) optical parametric oscillator (OPO) are reported. The OPO was pumped with a modulated, high repetition rate Q-switched Nd:YAG laser, which produced an average power of 20 W in a near-diffraction limited beam. The broadband full width half maximum (FWHM) of the OPO was measured to be 120 nm, with an average power output of 7.7 W. Using an air-spaced etalon in combination with a quartz birefringent filter as line-narrowing elements, this decreased to a line-narrowed average power of 4.5 W, with a full width half maximum (FWHM) of 3 nm. Experimental results indicate that the power loss from the OPO is proportional to the residual loss of the line-narrowing elements in the OPO cavity.

Heat generation and laser performance were studied in Nd:YAG oscillators pumped with a Ti:Sapphire laser in two regimes: band pumping at 802nm and direct pumping at 885nm. Slope efficiencies of 52% and 57%, when pumped at 802nm and 885nm, were obtained, respectively. Heat per unit laser output was found to be 27% lower when pumped at 885nm (direct pumping regime) as compared to traditional band pumping around 808nm.

High-average power solid-state lasers use Nd or Yb lasants doped into a variety of host materials. Desirable properties for such materials include favorable spectroscopy, thermomechanical and thermo-optical parameters, and availability of the host material in large size and good quality. A laser designer often faces difficult choices because no combination of dopant and host materials incorporates all of the most desirable properties. This work presents a comparative study of gain media for diode-pumped, high-average power solid-state disk lasers. Relative performance of Nd and Yb doped into several host media is evaluated under several pump conditions.

A grazing incidence geometry was used tom ake compact, high power, efficient TEM₀₀, Nd:YVO₄ oscillators and amplifiers. A side-pumped Nd:YVO₄ laser based on a grazing incidence cavity design, pumped with a 50 W diode bar, achieved 30% optical to optical efficiency at 50 kHz and M²= 1.4 x 1.1 output. The alser was acousto-optically Q-switched and was operated at repetition rates from 20 to 100 kHz, as well as operating continuous-wave (CW). Multiple cavity designs were developed to optimize performance for short (<10ns) and longer (>30ns) pulse durations. 15 W of TEM₀₀ output was generated at 50 kHz and used to pump a periodically poled lithium niobate (PPLN) optical parametric oscillator (OPO), generating 5 W of eye safe output at 1.5 μm. This oscillator/OPO system was packaged on a 4 x 6 inch optical platform. Using an oscillator/amplifier/amplifier configuration, 30 W of 1.064 μm output power was generated at 50kHz and subsequently converted in an OPO to 10.25 W of eye safe output in a PPLN OPO. This work demonstrates that the side-pumped grazing incidence geometry scales to high power and maintains M² and efficiency while fitting in a compact package.

We have demonstrated the feasibility of cooling high power solid-stae lasers with diamond windows, whose thermal conductivity is about two orders of magnitude higher than sapphire's. An output power of 200Watt was achieved froma single Nd:YVO₄ slab in a zigzag configuration when pumped with 600Watt diodes at 808nm. The maximum output power reported in the literature with conventional cooling schemes is about 50W. A 2.3x4x24mm³ slab was pumped from its broad side (4x24 mm²) through a 0.3mm thick optical diamond window placed in close contact with the lasing crystal. The diamond window, held in a water-cooled copper housing acted as a heat conductor. The other broad side of the crystal was cooled directly by its water-cooled copper housing. Since pumping and cooling were along the same axis, a Cartesian thermal gradient was achieved, while the zigzag scheme was used to minimize thermal lensing. By using a BBO Q-switch, 70Watt average power was obtained at 20kHz with a pulse width of 19msec and with a beam quality of 3 and 12 times diffraction limit in the zigzag and transverse directions respectively. The output of a two-head configuration was 295Watt.

We have studied theoretically the depolarization thermally induced in an optical medium with disc or rectangular (slabs) geometry. Analytical dependences of the thermally induced depolarization in different Faraday devices on radiation power and on aspect ratio of slab or disc are obtained. Conditions at which the use of slabs or discs instead of rods allows creation of different Faraday devices operating at multikilowatt average power level are found. The emergence of high-quality TGG ceramics will help advance to even higher powers.

To improve the efficiency of laser phacoemulsification we developed a compact, high-repetition-rate, high-average-power, diode-pumped, 2.94 μm TIR-cavity Er:YAG laser system. Laser parameters of 19.4% slope efficiency, 5 W of average output power at up to 300 Hz repetition rate and more than 1.5 W at 1 kHz are demonstrated. The special design results in low thermal lenses of 1.9 Dpt/W. This is a good condition for high laser system scalability.

Laser micromachining has become a key enabling technology in the ever-continuing trend of miniaturization in microelectronics, micro-optics, and micromechanics. New applications have become commercially viable due to the emergence of innovative laser sources, such as diode pumped solid-state lasers (DPSSL), and the progress in processing technology. Examples of industrial applications are laser-drilled micro-injection nozzles for highly efficient automobile engines, or manufacturing of complex spinnerets for production of synthetic fibers. The unique advantages of laser-based techniques stem from their ability to produce high aspect ratio holes, while yielding low heat affected zones with exceptional surface quality, roundness and taper tolerances. Additionally, the ability to drill blind holes and slots in very hard materials such as diamond, silicon, sapphire, ceramics and steel is of great interest for many applications in microelectronics, semiconductor and automotive industry. This kind of high quality, high aspect ratio micromachining requires high peak power and short pulse durations.

We measured the resonator insertion losses, slope efficiencies and output power of six Nd doped Y₃Al₅O₁₂ (YAG)laser crystals with and without chemical etching. It was found that chemical etching lowered the insertion losses and increased the slope efficiency. Point defects were investigated by positron annihilation spectroscopy (PAS). PAS depth profiles showed that the etching efficiently removed near surface atomic-scale defects. The results suggested that chemical etching is an effective means to improve lasing properties of Nd:YAG crystals, reduce the thermal loading and increase the strength.

The essential difference of ceramics from a single crystal is that crystal axes in each grain comprising ceramics are arbitrarily oriented. We apply quaternion formalism (instead of traditional Jones matrix formalism) to describe depolarization of laser beam. This allows us to derive analytical expressions for depolarization ratio for uncompensated case and for all known compensation techniques as well. The analytic results, we have got, are in good agreement with numerical ones. It has been shown, that ceramic is almost equivalent to [111] crystal if the ratio of the rod length to grain length is about 300 or more. In particular, uncompensated depolarization is inversely proportional to this ratio. The latter is an important consequence of the random nature of thermally induced birefringence in ceramics.

The ALMDS (Airborne Laser Mine Detection System) has been developed utilizing a solid-state laser operating at 532nm for naval mine detection. The laser system is integrated into a pod that mounts externally on a helicopter. This laser, along with other receiver systems, enables detailed underwater bathymetry. CEO designs and manufactures the laser portion of this system. Arete Associates integrates the laser system into the complete LIDAR package that utilizes sophisticated streak tube detection technology. Northrop Grumman is responsible for final pod integration. The laser sub-system is comprised of two separate parts: the LTU (Laser Transmitter Unit) and the LEU (Laser Electronics Unit). The LTU and LEU are undergoing MIL-STD-810 testing for vibration, shock, temperature storage and operation extremes, as well as MIL-STD-704E electrical power testing and MIL-STD-461E EMI testing. The Nd:YAG MOPA laser operates at 350 Hz pulse repetition frequency at 45 Watts average 532nm power and is controlled at the system level from within the helicopter. Power monitor circuits allow real time laser health monitoring, which enables input parameter adjustments for consistent laser behavior.

To have a complex view on giant pulse generation, a more precise computer model of the build-up Q-switch pulse in solid-state laser was realized. As the time starting point of the rate equation calculation, the moment of a flashlamp trigger was chosen. A set of four main differential rate equations describes the energy transfer from a pumping source - capacitor to an output giant pulse. Two laser active media, i.e. ruby and alexandrite, were examined with this model. An active Q-schwitching in both cases were realized by electro-optical Pockels cell based on KDDP (for ruby oscillator) or LiNbO₃(for the alexandrite laser) crystals. The numerical solution of the rate equations was compared with the measured experimental data and a good agreement has been obtained.

New Nd:SrWO₄ and SrMoO₄ crystals (45 mm and 33 mm of legnth, respectively) were investigated as Raman frequency converters of 50 picosecond Nd:YAG pulses and compared with already previously measured BaWO₄ and KGd(WO₄)₂(KGW) tungstate crystals (33 mm and 40 mm of length, respectively). A forward SRS action was achieved in both new crystals. During the experiment the threshold energy of stimulated Raman process, generated wavelengths, and conversion efficiencies were measured. Single-pass first Stokes conversion efficiencies reached 25% and 21% for Nd:SrWO₄ and SrMoO₄ crystals, respectively. These values were compared with the maximal first Stokes efficiencies of previously studied crystals measured in the same experimental setup yielding: BaWO₄ (η = 25% and KGW (η = 22%). As concerned the threshold - it was comparable for BaWO₄, Nd:SrWO₄, and SrMoO₄. The SRS effect in KGW crystal started for ~25% higher pump energy. Our study shows that new Nd:SrWO₄ and SrMoO₄ crystals are other promising materials for picosecond Raman generation.

The behavior of an electrooptic Q-switch in a high-average-power lsaer is presented. The linear optical absorption of laser radiation produces thermal gradient and consequent thermally-induced birefringence in the electrooptic crystal which disturbs Pockels cell performance. Depolarization losses of the resonator caused by thermally-induced birefringence in the KD*P crystals are experimentally measured.

We present practical modeling for edged-pumped high power solid-state slab lasers. Both analytic and ray tracing methods were used to analyze the distributions of absorbed pump power using real broad spectrum diode laser pump sources. The resulting thermal and stress distributions were calculated with finite element analysis. Our analyses include the temperature dependence of the gain medium’s thermal conductivity and expansion coefficient. Nd:YAG and Yb:YAG were then compared for use as gain media for high power solid state slab laser.

All-solid-state laser devices operating in the 1.5 - 1.6 μm wavelength range have many practical applications. The most notable of these is their use in optical telecommunications, but the current research drive is to increase the output power from high beam quality, solid-state devices for eye-safe applications such as laser range finding and target acquisition, remote sensing of trace elements in air, light detecting and ranging, medicine, metrology and atmospheric phenomena such as measurements of wind shear. Yb³⁺ ions are co-doped into the host material to improve the pumping efficiency by taking advantage of commercial InGaAs diode lasers emitting at 980 nm. The absorbed pump is then non-radiative transferred to the Er³⁺ ions, and rapidly decaying to the ⁴I_13/2 upper-laser level. Laser operation in Er,Yb co-doped systems has been dominated by glass hosts (in particular, phosphate) with attempts in crystalline materials yielding disappointing results despite their superior mechanical and thermal properties. In this paper we will present efficient diode-pumped laser operation of the crystalline host material Er,Yb:YCOB at 1.55 μm. By studying the energy transfer mechanisms of this material, we have identified the optimum dopant concentrations and 250 mW of continuous wave (cw) output in TEM00 transverse mode has been obtained with a 2mm crystal in an hemispherical cavity. Also, >150 mW cw has been obtained in a flat-flat cavity arrangement. The output coupling in each case was 1%. The slope efficiency of the laser was 21.9%.