This PDF file contains the front matter associated with SPIE Proceedings Volume 8604, including the Title Page, Copyright information, Table of Contents, Introduction (if any), and Conference Committee listing.

A continuous-wave deep-ultraviolet light source is demonstrated based on a grating-stabilized diode laser pump system and two consecutive nonlinear conversion stages. Using the crystal Potassium Fluoroberylloborate (KBBF), direct second-harmonic generation to 191 nm could be realized with an output power of up to 1.3 mW. The linewidth at this wavelength is estimated to be around 100 kHz. The emission can be tuned mode hop-free over 40 GHz. Our scheme can be easily extended to 193 nm or – given the availability of suitable fundamental sources – to wavelengths as small as 165 nm. These parameters make our light source an ideal tool for applications in deep-ultraviolet metrology and photoemission spectroscopy.

Diode Pumped Alkali Lasers (DPAL) are being scaled to powers of greater than 1 kW and intensities exceeding 30 kW/cm². We have demonstrated a pulsed potassium laser with pump intensities of 1 MW/cm² and efficiency exceeding 10%. At these higher pump intensities, nonlinear processes including two photon absorption and Stimulated Raman Scattering offer alternative wavelengths for these gas lasers. We have observed 1^st and 2^nd order Stokes and anti-Stokes lasing due to Stimulated Electronic Raman Scattering (SERS) in a potassium cell. When the pump is tuned about halfway between the fine structure levels of the 4 ²P state, an efficient hyper-Raman process dominates. Up to 12 mW of red light is produced at a pump input of 232 mW. The threshold for the hyper-Raman process is about 60 mW. This type of laser may be useful for beam propagation experiments where a tunable probe beam spectrally close to the main beam is desired. Two-photon absorption at wavelengths near then DPAL pump transition has also been observed and used to demonstrate lasing in the blue and mid infrared. The transmission of a scanning cw ring laser through a static Rb cell reveals two-photon absorbance of greater than 10%. An absolute determination of the two-photon absorption crosssections for the Rb 5 ²S – 4 ²D transitions are reported. The efficiency and operationally feasible of these alternative DPAL wavelengths is assessed.

We propose an efficient concept increasing the power of diode laser systems in the visible spectral range. In comparison with second harmonic generation of single emitters, we show that spectral beam combining with subsequent sumfrequency generation enhances the available power significantly. Combining two 1060 nm distributed Bragg reflector tapered diode lasers (M²_4σ ≤ 5.2), we achieve a 2.5-3.2 fold increase of green light with a maximum power of 3.9 Watts in a diffraction-limited beam (M²_4σ ≤ 1.3). Without any further stabilization the obtained power stability is within ± 2.6 %. The electro-optical and nonlinear conversion efficiencies at maximum performance are 5.7 % and 2.6 %/W, respectively. Due to the intrinsic wavelength stabilization of the diodes we achieve single-mode emission with a sidemode suppression < 15 dB and a spectral width as narrow as 5 pm. These results increase the application potential of green diode laser systems, for example, within the biomedical field. In order to enhance the power even further, our proposed concept can be expanded combining multiple diode lasers.

We report the development of a very compact, highly efficient, megawatt peak power 266 nm UV microlaser. It contains a specially designed passively Q-switched Nd:YAG/Cr⁴⁺:YAG microchip laser whose high output peak power of 13 MW enables us to perform wavelength conversion without using any optics before the nonlinear crystals. We achieve 73 % SHG conversion efficiency using a LBO crystal and 45% FHG conversion efficiency using a BBO crystal. As a result, we obtain 650 μJ, 4.3 MW peak power, 150 ps, 100 Hz pulse output at 266 nm. This palm-top size 266 nm UV microlaser will be useful for many applications.

We demonstrate a compact all-room-temperature picosecond laser source broadly tunable in the visible spectral region between 600 nm and 627 nm. The tunable radiation is obtained by frequency-doubling of a tunable quantum-dot external-cavity mode-locked laser in a periodically-poled KTP multimode waveguide. In this case, utilization of a significant difference in the effective refractive indices of the high- and low-order modes enables to match the period of poling in a very broad wavelength range. The maximum achieved second harmonic output peak power is 3.25 mW at 613 nm for 71.43 mW of launched pump peak power at 1226 nm, resulting in conversion efficiency of 4.55%.

Several watts compact CW green laser head without any cooling is demonstrated by combining CW fiber laser and PPMgSLT. Since the conventional high power visible laser has huge heat sources at its laser head, it requires air or water cooling. In addition, the optical system, which is mounted this type of head, has sometime problems of optical stability caused by those heat sources from the head. The laser head we demonstrated has three input and output ports of the laser light; fiber input of fundamental light (1064nm) from CW fiber laser, SHG (532 nm) output into free space, and fiber output of residual fundamental laser light. The size of laser head was 110mm X 78mm X 64mm (550cc). More than 25W of CW fundamental light from single mode fiber was focused into 30mm-long PPMgSLT device operated at 40 degree C. The linewidth of the laser was 0.09 nm at FWHM. 5W of 532 nm light was generated from PPMgSLT. Because of high power durability of PPMgSLT, it could be easily realized several watts of visible light generation by simple singlepass configuration. Residual fundamental light was separated by harmonic separator and was coupled into large core multi-mode fiber. As a result, there are no remarkable heat sources at the laser head. The stable green light from this head was confirmed without any cooling at the laser head. Since this configuration doesn’t affect any thermal turbulence in surroundings, the stability of the optical system would be improved by using this laser head.

The optical amplification and frequency conversion of a gain-switched 1532 nm distributed feedback (DFB) laser diode over a wide range of repetition rates are studied. A two stage Erbium fiber amplifier setup is pumped at 976 nm and operated at 1 to 80MHz pulse repetition frequency. The seed laser repetition rate is evaluated directly inside the pumping electronics to set the optimum pump power. Second-harmonic generation to 766 nm is achieved in a periodically poled lithium niobate bulk crystal. There is a high demand of several hundred milliwatt of picosecond pulsed laser power for stimulated emission depletion (STED) microscopy.

We demonstrated ultra-violet (UV) generation by launching 1040-nm picosecond pulses into a step-index fused-silica fiber without tapering. Even in a conventional step-index fiber, the phase mismatching between LP01 mode of the fundamental wave and higher-order mode of the third-harmonic wave can be reduced by increasing the index contrast. In addition, in the cladding mode, Cherenkov-type phase matching is made possible. Thus, although the phase-matching is not achieved rigorously, THG can occur locally enough to observe the third-harmonic signal clearly at the output. In the experiment, we launched a picosecond pulse train from a 1040-nm fiber laser into a commercially available stepindex fiber with high index contrast. The UV light was observed in the wavelength range of 347-390 nm, and the output power of UV components was increased with the third- and fourth-order dependence. Also, we observed the bright bluelight emission along the fiber, which was originated from the fluorescence due to the defect of SiO₂/GeO₂ radiated by UV light (generated by THG).

Intense terahetz (THz) pulses induce a photoluminescence (PL) flashes from undoped GaAs/AlGaAs quantum wells under continuous wave laser excitation. The number of excitons increases 10000-fold from that of the steady state. The THz electric field dependence and the relaxation dynamics of the PL flash intensity suggest that the strong electric field of the THz pulse ionizes trap states during the one-picosecond period of the THz pulse and release carriers existing in a giant reservoir containing many trap states in the AlGaAs layers.

Organic stilbazolium salt crystals pumped by intense, ultrashort mid-infrared laser have been investigated for efficient THz generation by optical rectification. In this paper we present our latest results in view of the generation of single-cycle and high-field THz transient in the THz gap (0.1-10 THz). The organic rectifiers like DAST, OH1 and DSTMS combine extremely large optical susceptibility with excellent velocity matching between the infrared pump and the THz radiation. Our simple collinear conversion scheme provides THz beams with excellent focusing properties and single cycle electric field larger than 1.5 MV/cm and magnetic field strength beyond 0.5 Tesla. The source can potentially cover the full THz gap at field strength which is barely provided by other THz sources. The THz pulse is carrier-envelope phase stable and the polarity of the field can be easily inverted.

We have demonstrated the comparison of terahertz (THz) time-domain spectroscopy (THz-TDS): a low-temperature grown GaAs photoconductive antenna (PCA) and ZnTe electro-optic (EO) sampling with 780-nm 1.3-ps laser pulses. As a result, the different detection limits up to approximately 0.8, 1.0, and 1.3 THz are obtained with a bow-tie, dipole antenna, and ZnTe crystal, respectively. In the PCA sampling, the frequency at main peak of the spectrum measured with the dipole antenna is higher than the one with the bow-tie antenna. The dynamic range of the power spectrum measured with the bow-tie antenna is higher than any other detection methods. In addition, we compare the PCA sampling with femtosecond laser pulses to the one with picosecond laser pulses in terms of the response of the PCAs.

We report a widely tunable terahertz source by using QPM-GaAs crystals pumped by a near-degenerate dual-wavelength KTP OPO around 2.127μm, based on difference frequency generation (DFG). The tunable THz radiation from 0.06 THz to 3.34 THz has been achieved in QPM-GaAs crystal with coherence length of 650 μm. The maximum output THz energy is 45 nJ with the peak power of 10 W at 1.68 THz, corresponding to the energy conversion efficiency of 5×10^-6 and the photon conversion efficiency of about 0.08%.

The output of a periodically poled lithium niobate (PPLN) optical parametric generator (OPG) is filtered using an off axis Fabry-Perot etalon. The filtered output is then parametrically amplified in the same PPLN crystal resulting in a tunable narrow-band infrared source. The PPLN OPG is pumped with a10 nsec pulse duration, 1.064 μm singlefrequency pump laser, with an output signal and idler determined by the PPLN periodicity. The polarization of the pump laser is rotated so that only a portion of it is phase matched on the first pass through the PPLN crystal. The portion that is phase matched generates a signal that is directed to an off-axis Fabry-Perot etalon, which, in the off-axis configuration has a narrow bandwidth reflection. The pump beam is transmitted through a quarter wave plate and reflected with a mirror so that when passed back through the PPLN crystal, its polarization is rotated 90 degrees with respect to the input. Hence the portion of the pump not phase matched on the first pass is now phase matched for the second pass. The reflected and filtered signal is co-aligned with the pump resulting in a narrow bandwidth amplified signal. This system is capable of generating narrow bandwidth over the tuning range of the PPLN crystal and is only restricted by the etalon reflectivity range. We demonstrate tunability in the 1.4 μm -1.6 μm signal range (3.0 μm-4.4 μm idler range), which is restricted by our etalon reflectivity.

High pulse energies in the mid-IR with a comfortable tuning possibility are required in a number of areas, including remote sensing, medicine and counter measure applications. Frequency converters based on the crystal ZnGeP₂ (ZGP) are widely used for generating tunable IR radiation in the 2.5 μm - 12 μm region. ZGP possesses high nonlinearity, however, due to its limited transparency range it requires pump wavelengths longer than 2 μm. A significant drawback of ZGP and of most other IR non-linear crystals is a low damage threshold of ~ 1 J/cm² for nanosecond pulses. Therefore nanoseconds OPOs at pulse energies in the 10 mJ – 100 mJ range require large diameter pump beams to reduce the risk of optical damage to the crystal. We used the “Rotated-Image, Singly resonant, Twisted-RectAngle” (RISTRA) ring cavity concept to improve the beam quality of the OPO stage. A Tm³⁺ fiber laser pumped Ho³⁺:LuLiF₄ (Ho³⁺:LLF) MOPA system was developed delivering > 100 mJ at 2053 nm in TEM₀₀ operation at a repetition rate of 100 Hz. Using a RISTRA as a single OPO stage we demonstrated an overall OPO pulse energy of 23.8 mJ in the wavelength region 3 μm - 5 μm at a pump energy of about 45.6 mJ and a repetition rate of 100 Hz. The beam quality was measured to be M² ~ 2.5.

Parametric generation in an endlessly single-mode photonic crystal fiber can be a simple and efficient way to generate tunable visible and mid-infrared radiation. In this manuscript we report on a visible light source that is tunable from 628nm to 661nm with up to 25% conversion efficiency. This was obtained by tuning the parametric pump from 1030nm to 1055nm in a 1.6m long LMA-10 PM photonic crystal fiber. At the same time, the source generates mid-infrared radiation that can be tuned from ~2.65μm to ~2.9μm. A further increase of the tunable range of both the visible and midinfrared is possible simply by extending the pump tuning range.

Common optical fibers are randomly birefringent, and solitons traveling in them develop random polarization states upon propagation. However it is desirable to have solitons with a well-defined polarization. We analyzed the two coupled propagation equations in a circularly birefringent fiber. Our equations included the soliton self frequency shift. For our best knowledge this set of equation was analyzed for the first time. We performed a transformation of equations which reduces them to a form of perturbed Manakov task. The difference between our equations and the integrable Manakov case was considered as a perturbation. The perturbation method gives us an equations for evolution of the polarization state of pulse. The evaluation equation shows that in a circularly birefringent (twisted) fiber the cross–polarization Raman term leads to unidirectional energy transfer from the slow circularly polarized component to the fast one. The magnitude of this effect is determined by the product of birefringence and amplitudes of both polarization components. Thus, solitons with any initial polarization state will eventually evolve stable circularly polarized solitons. We also solved equations using a split-step Fourier method. The parameters of a standard fiber were used with delay between left- and right- circular polarizations of 1 ps/km that corresponds a fiber twisted by 6 turns/m.

We present a detailed study of power scaling in polarization-maintaining Raman fiber amplifiers operating at 1178 nm since this wavelength can be frequency doubled into 589 nm for sodium guide star applications. We confirm experimentally that the optimized output signal at SBS threshold scales linearly with the pump power. We also present results from numerical and experimental studies investigating the scalability of Raman fiber amplifiers with seed power. Both co-pumped and counter pumped two-stage amplifiers utilizing acoustically tailored fiber for SBS suppression were constructed and studied. For the former configuration spectral broadening was observed, while the latter configuration provided 22 W of single-frequency output. Finally, we show results of a phase-modulated amplifier generating multiple spectral lines separated by 886 MHz, which corresponds to the spectral separation of the sodium D2a, and D_2b lines after frequency doubling in a nonlinear cavity.

The combination of frequency combs and quantum cascade lasers is opening new opportunities in the field of precision spectroscopy in the mid-infrared. Frequency combs allow quantum cascade lasers to be referenced to a highly repeatable, precise and absolute frequency axis. Repeatability is a key feature to obtain high quality measurements of absorption profiles and thus accurate determination of spectroscopic parameters, while absolute frequency calibration makes it possible the comparison of spectroscopic data acquired in different laboratories and at different times, as well as comparison with theoretical predictions or existing databases. This work reviews some of the main results achieved at 4.3 μm by investigation of a manifold of rovibrational lines of CO₂. Spectroscopic parameters such as line-centre frequencies, line intensity factors, pressure shift and pressure broadening coefficients are retrieved with an unprecedented quality from the metrological point of view.

It has recently been shown that it is possible to upconvert infrared images to the near infrared region with high quantum efficiency and low noise by three-wave mixing with a laser field [1]. If the mixing laser is single-frequency, the upconverted image is simply a band-pass filtered version of the infrared object field, with a bandwidth corresponding given by the acceptance parameter of the conversion process, and a center frequency given by the phase-match condition. Tuning of the phase-matched wavelengths has previously been demonstrated by changing the temperature [2] or angle [3 Keywords: Infrared imaging, nonlinear frequency conversion, diode lasers, upconversion ] of the nonlinear material. Unfortunately, temperature tuning is slow, and angle tuning typically results in alignment issues. Here we present a novel approach where the wavelength of the mixing field is used as a tuning parameter, allowing for fast tuning and hence potentially fast image acquisition, paving the way for upconversion based real time multispectral imaging. In the present realization the upconversion module consists of an external cavity tapered diode laser in a Littrow configuration with a computer controlled feedback grating. The output from a tunable laser is used as seed for a fiber amplifier system, boosting the power to approx. 3 W over the tuning range from 1025 to 1085 nm. Using a periodically poled lithium niobate crystal, the infrared wavelength that can be phase-matched is tunable over more than 200 nm. Using a crystal with multiple poling periods allows for upconversion within the entire transparency range of the nonlinear material.

We present high resolution upconversion of incoherent infrared radiation by means of sum-frequency mixing with a laser followed by simple CCD Si-camera detection. Noise associated with upconversion is, in strong contrast to room temperature direct mid-IR detection, extremely small, thus very faint signals can be analyzed. The obtainable frequency resolution is usually in the nm range where sub nm resolution is preferred in many applications, like gas spectroscopy. In this work we demonstrate how to obtain sub nm resolution when using upconversion. In the presented realization one object point is imaged through the upconverter. Assuming homogeneous spherical emission from the object point, the upconverted radiation will carry the spectral information as con-centric rings. From the optical path length and dispersion properties of the nonlinear material, the acceptance bandwidth of the upconversion process is calculated. It is then straightforward to deduce the spectral information of the light emitted from the object point by a simple analysis of the upconverted radiation. In order to increase resolution, a scanning Fabry-Perot etalon is inserted in a collimated geometry of the upconverted light generated by the crystal. The etalon is designed with a free-spectral range larger than the bandwidth of the upconversion process. Hence, the spectral resolution is now set by the finesse of the etalon. Based on this approach a spectral resolution of 0.2 nm has been reached around 2.9 μm. We demonstrate high resolution spectral performance by observing emission from hot water vapor in a butane gas burner.

We have performed intracavity molecular spectroscopy of water vapor, isotopic carbon dioxide, methane, acetylene, carbon monoxide, formaldehyde and other gases using broadband mid-IR sync-pumped OPO sources (PPLN-based OPO pumped by a femtosecond Er-fiber laser, or OP-GaAs-based OPO pumped by a femtosecond Tm-fiber laser) operating near degeneracy, with up to 2.5–6.1 μm instantaneous bandwidth. We found that the measured spectral line shapes may show dispersive features. The measured spectra were compared to a simple model, based on the intracavity round-trip dispersion, and excellent agreement between theory and measurements was found. Detection limits in the ppb-range were demonstrated.

Orientation-patterned GaP is a promising nonlinear material for frequency conversion in the mid and longwave IR (2-5 μm and 8-12 μm) by quasi-phase matching. As an alternative to OPGaAs, OPGaP has the advantage of having lower two-photon absorption in the convenient pumping range 1 – 1.7 μm. We report recent results on development of thick QPM GaP for high power tunable laser sources radiating in the mid IR. Two are the major challenges to producing OPGaP: development of simple techniques for preparation of patterned templates and a technology for fast epitaxial growth of thick, high quality GaP on these templates. The focus was to adapt/simplify the wafer fusion process for OPGaP template preparation. Then increase the growth rate and layer thickness of regrown material, while maintaining vertical domain propagation. The growth experiments were conducted in a horizontal quartz reactor, using a standard hydride vapor phase epitaxial process. The growth was performed on: (i) plain (100) GaP; (ii) half-patterned (HP) and (iii) orientation-patterned (OP) templates, fabricated on (100) GaP. Up to 370 μm thick layers with high crystal and optical quality were reproducibly grown on plain material. Growth on HP templates resulted in up to 470 μm thick layers with rectangular mesa‟s shape. These results were used to determine the optimal substrate and pattern orientations. HVPE growth on OP templates achieved stable growth rates of 50-70 μm/h with domain walls propagating vertically, following the periodicity of the initial pattern, and resulted in the first 350 μm thick device quality OPGaP.

This paper analytically describes the surface plasmon enhanced very low threshold second harmonic generation formed by a 29 nm thin gold layer is sandwiched between a BK₇ prism plane and 20 nm thin GaAs layer. Here the electric field with incident optical radiation of picowatt level is amplified upto milliwatt level through surface plasmon phenomenon at off resonance condition. This amplified output further coupled to a whispering gallery resonator, which facilitates the generation of second harmonic for an incident optical radiation of picowatt level. In this proposed configuration with an incident optical power of 94.6 pW generated second harmonic through whispering gallery resonator found to be 14.6 mW.

Tantalum pentoxide (Ta₂O₅) is a promising material for both linear and nonlinear integrated optical device fabrication due to its high refractive index, low absorption over a wide wavelength range, high nonlinear refractive index, large value of chi 3 and high optical damage threshold. In particular Ta₂O₅ rib and ridge waveguides provide an interesting platform for solid state Laser applications. Waveguide surface roughness and sidewall slope profile can induce significant scattering loss reducing the efficiency of the device. Optimization of these parameters is key to obtain ultimate performance of the final device. In this paper, we present a method and photolithographic mask layout suitable to allow easy measurement of optical propagation loss for planar rib or ridge waveguides. The procedure is equivalent to the standard ‘cut- back’ method, but one that does not requiring devices to be cleaved and polished multiple times. The mask incorporates a set of narrow nano-wire waveguides coupled by tapered waveguide sections to wide input /output guides. The lengths of the central nano-wire section are determined precisely by the lithographic mask. The layout is designed to allow losses of each sub-component such as taper sections and input waveguides to be removed from the measurement, giving accurate measurement of loss in the central nanowire section of the guide. Optical loss measurements are presented for Ta₂O₅ nanowire rib waveguides. Loss was found to be dependent on lengths and widths of nanowire waveguide sections. Measured propagation losses for the rib waveguides are found to be just slightly higher than loss of a Ta₂O₅ slab waveguide as measured by a commercial Metricon system, validating the low loss nanowire waveguide fabrication processes.

We examine the physics of traveling-wave photon-phonon coupling within nanoscale silicon waveguides and explore a host of new Brillouin-based signal processing technologies enabled by tailorable stimulated Brillouin processes in silicon photonics. Theoretical analysis of Brillouin coupling at sub-wavelength scales is presented, revealing that strong light-boundary interactions produce large radiation pressures mediated Brillouin nonlinearities. Experimental results demonstrating stimulated Brillouin scattering in silicon waveguides for the first time are also presented, revealing 1000 times larger forward stimulated Brillouin gain coeffcients than any prior system.

Graphene placed in a magnetic field possesses an extremely high mid/far-infared optical nonlinearity originating from its unusual band structure and selection rules for the optical transitions near the Dirac point. Based on quantum-mechanical density-matrix formalism, here we study the linear and nonlinear optical response of graphene in strong magnetic and optical fields. We calculate the power of coherent terahertz radiation generated as a result of four-wave mixing in graphene. We also show that even one monolayer of graphene gives rise to appreciable nonlinear frequency conversion efficiency and Raman gain for modest intensities of incident infared radiation.

In the modern intelligent fiber Bragg grating (FBG) sensing network, the spectrum interrogation should not only have high speed and wavelength resolution, but also use the limited spectrum resource efficiently. In this paper, we propose a spectrum interrogation technique by using a wavelength-division multiplexing (WDM) to optical time-division multiplexing (OTDM) converter, which could map the sensing signals from the wavelength domain to the time domain quickly and efficiently. The converter consists of an electro-optic switch, time delay unit and a multi-wavelength converter. The continuous WDM sensing signals are converted into pulsed WDM signals by using a 10 GHz LiNbO₃ intensity modulator as the electro-optic switch. A segment of single mode fiber (SMF) is used as the time delay unit for delaying the pulsed WDM signals overlapped in time. By using a high speed 40 GHz electro-absorption modulator (EAM) as the multi-wavelength converter, the pulsed and delayed WDM signals are converted into OTDM signals with the same wavelength. At last, the light signals after demodulation are detected by photoelectric detector (PD) which has high response speed and low cost. The mapping of the wavelength domain to the time domain in our spectrum interrogation can allocate the spectrum resource efficiently and dynamically. It is experimentally demonstrated that two signals in wavelength domain can be converted into time domain signals carried by a wavelength with a roughly equal conversion efficiency.

An coherent terahertz (THz) source was reported by quasi-phase matched different frequency generation in a stacked GaAs wafers pumped by one CO₂ laser with dual-wavelength output. The THz generation was increased with the increase of the number of GaAs wafers. The maximum single pulse energy of 12 nJ was generated at a frequency of 0.94 THz (319 μm) by using ten GaAs wafers, corresponding to a peak output power 200 mW

This paper reports the 90° phase-matched fourth-harmonic generation of the CO₂ laser wavelength at 10.5910 μm in BaGa₄S₇. The 1.4 cm long BaGa₄S₇ crystal used in the present experiment was cut at θ=9.2° in the xz(=bc) plane. The pump source was the second harmonic of the wave-guide CO₂ laser (10.5910 μm) operating with an average output power of 18.3 W at 130 kHz. By focusing the 7.6 W, 5.2955 μm pulses (peak power is 6kW with 10 ns pulse duration) generated from the 2 cm long AgGa_0.65In_0.35Se₂ crystal into the BaGa₄S₇ crystal (θ_PM=9.9°) with the 6 cm focal length ZnSe lens, the maximum average output power of 0.3 W was obtained at 2.6478 μm without any damage to the crystal. In addition, the new Sellmeier equations of BaGa₄S₇ are presented.

The hybrid microstructured optical fibers (HMOFs) are emerging due to their capability of tailoring the dispersion. The chromatic dispersion and other related optical properties, such as optical mode confinement and effective index, have been calculated using the finite element method. We have realized four zero dispersion wavelengths (ZDWs) of 1566, 1605, 1726 and 1790 nm. The signal and idler wavelength dependent on pump wavelength is calculated. The gain bandwidth is 134 nm for the pump wavelength of 1761 nm between third and fourth ZDW. The supercontinuum generation is studied for the pump wavelength 1761 nm.

It is well known that lithium niobate (LiNbO₃) has excellent characteristics for efficient tunable/broadband THz-wave generation. Over the last few years, we have investigated novel THz-wave sources based on MgO-doped LiNbO₃ (MgO:LiNbO₃), and have succeeded in developing a tunable picosecond THz-wave source by using a novel pentagramshaped pump-enhancement cavity. One of the limiting factors in efficient THz-wave generation is the strong absorption by MgO:LiNbO₃ in THz-wave region. To overcome this problem, we employ a surface-emitted configuration which consists of a trapezoidal MgO:LiNbO₃ crystal and a pump-enhancement cavity folded in the shape of a pentagram. The pentagram-shaped cavity is designed for the noncollinear dual resonance of both pump and one of the down-converted waves. As a result, 1.5-ps pump pulses from a mode-locked Ti:sapphire laser operating at 780 nm allow tunable THzwave generation via parametric down-conversion resulting from stimulated phonon-polariton scattering in the MgO:LiNbO₃ crystal. By slightly translating the position of one of the cavity mirrors, we experimentally find that the THz-wave frequency is tunable in the range from 0.1 to 3.5 THz with the average output power of dozens of nanowatts. The maximum THz-wave average power is up to 40 nW around 2 THz at the pump power of 800 mW, which is several times higher than the THz-wave output generated by using rectangular MgO:LiNbO₃ crystals for Si-prism-coupled configuration under the same pump condition.

Hg_0.35Cd_0.65Ga₂S₄ and Hg_0.52Cd_0.48Ga₂S₄ have been found to be phase-matchable for type-1 second-harmonic generation (SHG) of the fundamental radiation at 2.907-5.453 μm and 2.423-6.725 μm, respectively. The Sellmeier equations for HgGa₂S₄ and CdGa₂S₄ that reproduce well these experimental results as well as the published data for the Cr:forsterite laser (1.25 μm)-pumped Hg_0.35Cd_0.65Ga₂S₄ optical parametric generator (OPG) and the Ti:Al₂O₃ laser (0.820 μm)-pumped Hg_0.52Cd_0.48Ga₂S₄ optical parametric amplifier (OPA) at 5.59-9.12 μm are presented.

Recently, we solved the coupled-mode equations for Bragg scattering (BS) in the low- and high-conversion regimes, but without the effects of nonlinear phase modulation (NPM). We now present solutions and Green functions in the low-conversion regime that include NPM. We find that NPM does not change the lowest-order conversion efficiency, but prevents complete separability (freedom from temporal entanglement). This problem is overcome to some degree by pre-chirping the pumps, which mitigates the effects of NPM. We conclude that arbitrary reshaping of the output modes and nearly complete separability are still possible, even when the effects of NPM are included. Finally, the effects of using different input signals are considered, and we conclude that using the natural input modes of the system drastically increases the efficiency.

By pumping the 8mm long HgGa₂S₄ crystal cut at θ = 67.5° and φ = 0° with the Nd:YAG laser in the double-pass SRO (singly resonant oscillator) scheme, we have generated 410mW output power (80mW at 4.180μm and 330mW at 1.428μm) at 30Hz. The pump to output conversion efficiency was 17%. In addition, by heating the HgGa₂S₄ crystal from 20° to 120° at normal pump incidence (θpm = 67.5°), we have generated the tunable outputs in the 1.413～1.428μm and 4.180～4.311μm range.