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We have applied a new simplified combination of numerical methods for studying the time and three-dimensional space dependence of quasi-three-level Yb3+:Yttrium Aluminum Garnet (YAG) end-pumped lasers passively Q-switched by a Cr4+:YAG saturable absorber. We base our 3-D model on iterative, efficient, time- and space-dependent numerical propagation of the optical field through the laser cavity. The complex-valued laser field is coupled to the Yb3+:YAG and Cr4+:YAG media via complex optical permittivities, which are subsequently altered by gain/loss intensity saturation. The calculation is simplified using the radial symmetry of the system, with the cavity round-trip time as the smallest increment for updating the permittivities. We also include the effects of field diffraction in an intra-cavity air gap. For specified CW spatial pump conditions, self-consistent repetitively pulsed solutions for the laser field in a flat-flat or flat-convex mirror cavity are found with no ad hoc laser mode size or shape assumptions; these solutions are not Gaussian modes. We concentrate on compact lasers with multi-Watt average output power, operating at modest pulse energy (~1.0 mJ), high repetition rate (~5 kHz) and short pulse duration (~1.5 ns). Typical room-temperature pump-to-laser slope power efficiencies exceeding 50% are predicted, depending on laser pump and cavity loss parameters. Model results agree well with recently published experimental data.

A 1908 nm Tm:YLF laser, passively Q-switched (PQS) using a Cr:ZnS saturable absorber, is shown to generate significantly higher pulse energy and peak power than previously reported. Using a compact 13 cm-long, plano-concave resonator cavity, the end-pumped Tm:YLF laser generated 15.6 mJ, 26ns FWHM pulses, corresponding to a peak power of 600 kW, with a 0.5kHz PRF, and 7.8W average power. A 10 cm-long laser generated 10 mJ, 20 ns long pulses, with a 1 kHz PRF and 10 W average power. A laser utilizing the shortest, 4.5 cm-long cavity, generated 7 ns pulses with a pulse energy of 3.7mJ. All of the laser configurations incorporated a Volume Bragg Grating (VBG) high reflectivity cavity mirror to lock the laser wavelength and polarization. To minimize the energy fluence at Cr:ZnS saturable absorbers (To=88.6% and To=91.6%), they were placed near the concave output coupler where that laser mode field area of the plano-concave laser resonator was at its maximum.

We describe a compact mid-IR source utilizing an intracavity, non-critically phase matched potassium titanyle arsenate (KTA) optical parametric oscillator (OPO) placed inside a passively Q-switched (PQS), 1.064 µm Nd:YAG laser resonator. A 45-degree dichroic beam splitter was employed to split the 1.064 µm resonator leg from the 1.5 μm/3.5 μm KTA OPO cavity that was singly resonant for the 1.5 μm signal. The 20 mm long KTA crystal was placed in the shared-path section of both cavities, with the KTA OPO output coupler partially reflective at 1.5 μm, and highly transmitting at 3.5 μm. With the Nd:YAG pumped by a 3-λ 12-bar diode stack at 5 Hz PRF, the KTA OPO generated 23.1 mJ signal pulses at 1.5 μm and 9.8 mJ idler pulses at 3.5 μm. To further increase the 3.5 μm energy, a cadmium silicon phosphide (CSP) optical parametric amplifier (OPA), phase matched for 1.5 μm-pumped amplification of 3.5 μm radiation, was placed immediately after the KTA OPO output coupler. A maximum 3.5 μm pulse energy of 13.2 mJ was measured after the OPA, with an additional 4.2 mJ generated at 2.8 μm. The 3.5 μm pulses had a measured temporal duration (FWHM) of 27 ns, corresponding to a peak-power of approximately 490 kW. This paper will detail the Nd:YAG pumped intracavity KTA OPO / CSP OPA and optimization of its performance as a pulsed midIR source.

We demonstrate operation of a compact, passively Q-switched Yb:YAG laser producing 10W average power at 1030nm in an 8.5kHz train of 1.2mJ, 1.6ns pulses. The laser is cw end-pumped with a fiber-coupled wavelength-stabilized 940nm diode. The pump light from the 105m diameter (0.1 NA) pigtail is collimated using a short focal length lens and directed into a 3mm long, 1mm thick 10 at.% Yb:YAG crystal. The saturable absorber is a Cr4+:YAG crystal with 76% unsaturated transmission. The laser’s slope efficiency is 52% and the optical-to-optical conversion efficiency is 33% at a pump power of 30W.

A diode-end-pumped Tm:YLF laser, passively Q-switched (PQS) with a Cr:ZnS saturable absorber, generated 10 mJ, 29 ns-long pulses at 1.9 μm, corresponding to a peak power of 350kW. A PQS laser operated at a maximum pulse repetition frequency (PRF) of 1 kHz, generating an average power of 10 W. The demonstrated pulse energy and average power represent significant increases over previous results with PQS Tm-doped lasers, and the 10 mJ pulse energy is comparable to that of much more complex actively Q-switched versions of such lasers. Using a cadmium silicon phosphide (CSP) optical parametric oscillator (OPO), the laser output was converted to 3.5-4.2 μm mid-IR emission. The OPO exhibited an optical efficiency of 64%, and generated 6W of mid-IR power.

We describe a compact mid-IR source utilizing an intracavity, non-critically phase matched potassium titanyle arsenate (KTA) optical parametric oscillator (OPO) placed inside a passively Q-switched (PQS), 1.06μm Nd:YAG laser resonator. The 20mm long KTA intracavity OPO was singly resonant, with the output coupler coated for partial reflectivity of 60% at the 1.5μm signal emission and for high transmission at the 3.5μm idler wavelength. With the Nd:YAG pumped by a 3-λ 12-bar diode stack at 5Hz PRF, the OPO generated a maximum 20mJ signal pulse at 1.5μm and 8.8mJ idler pulse at 3.5μm. A cadmium silicon phosphide optical parametric amplifier (OPA), phase matched for 1.5μm-pumped amplification of the 3.5μm OPO idler, was placed in the near field of the intracavity OPO to further increase the mid-IR pulse energy. A maximum 3.5μm pulse energy of 12.1mJ was measured after the OPA, with an additional 4.0mJ measured at 2.8μm. The 3.5μm pulses had a temporal duration of 20ns, corresponding to a peak-power of 605kW. This paper will detail the Nd:YAG pumped intracavity KTA OPO/CSP OPA and optimization of its performance for maximizing the mid-IR pulse energy.

We characterize several configurations of compact, Q-switched, 1.5 um lasers based on Er/Yb doped glass. Such lasers are required for eye-safe laser range-finders (LRF), laser markers, and illuminators for 3D and gated imaging. While 1-3 Hz pulse repetition frequency (PRF) is adequate for LRFs, the other applications require much higher PRFs to achieve near-real-time image refresh rates. Lasers described here utilize Er/Yb glass active elements, side-pumped by a 940 nm laser diode bar, or end-pumped by a fiber-coupled laser diode, and made use of active or passive Q-switching (PQS) techniques. Active Qswitching is implemented with resonant scanning mirror, and PQS utilizes Co:Spinel saturable absorbers. Q-switched pulse energies of 5mJ and 3mJ are achieved with side-pumping and end-pumping, respectively. An optical efficiency of over 3.7%, the highest to our knowledge for a PQS Er/Yb glass laser, is measured for the end-pumped implementation. When configured to generate 1mJ, the endpumped PQS laser operates over a 2-25 Hz PRF range, with nearly constant pulse energy and optical efficiency. Features and advantages of the various laser configurations are compared.

We describe mid-IR sources utilizing a CSP Optical Parametric Oscillator (OPO) directly pumped by a high efficiency 1.94 μm Tm:YAP Q-switched laser. The OPOs, constructed using the latest generation CSP crystals with low 1.94 μm absorption, were operated at near-degeneracy with mid-IR output in the 3.6-4.2 μm range. Compact Q-switched Tm:YAP lasers, implemented using both a Cr:ZnS saturable absorber Q-switch or a mechanical Q-switching (MQS) technique, were constructed with the Q-switching method’s impact on OPO performance evaluated. Resonant effects were observed for MQS that were absent in the passively Qswitched (PQS) experiment. It was determined that optimizing the OPO resonator length, relative to the cavity length of the Tm:YAP laser, maximized the OPO conversion efficiency. An optimized OPO, pumped at an incident 1.94μm MQS laser power of 7.6W, generated an average mid-IR power of 4.6 W, corresponding to an optical conversion efficiency of 60%, and an overall optical efficiency for mid-IR generation of 21% relative to diode power incident on the Tm:YAP.

We describe generation of near-infrared (944nm, 970nm), blue (472nm, 485nm), and UV (236 nm) light by frequency up-conversion of 2 μm output of a compact and efficient passively Q-switched Tm:YAP laser. The Tm:YAP laser source was near diffraction limited with maximum Q-switched pulse peak power of 190 kW. For second harmonic generation (SHG) of NIR, both periodically poled lithium niobate (PPLN) and lithium tri-borate (LBO) were evaluated, with 58% conversion efficiency and 3.1 W of 970 nm power achieved with PPLN. The PPLN 970nm emission was frequency doubled in 20mm long type I LBO, generating 1.1 W at 485nm with a conversion efficiency of 34%. With LBO used for frequency doubling of 2.3 W of 1888 nm Tm:YAP output to 944nm, 860mW was generated, with 37% conversion efficiency. Using a second LBO crystal to generate the 4th harmonic, 545mW of 472nm power was generated, corresponding to 64% conversion efficiency. To generate the 8th harmonic of Tm:YAP laser emission, the 472nm output of the second LBO was frequency doubled in a 7mm long BBO crystal, generating 110 mW at 236nm, corresponding to 21% conversion efficiency.

Highly efficient, diode pumped Tm:YAP lasers generating emission in the 1.85-1.94 μm range are demonstrated and characterized. Laser optical efficiencies of 51% and 45%, and electrical efficiencies of 31% and 25% are achieved under CW and Q-switched operation, respectively. Laser performance was characterized for maximum average powers up to 20W with various cavity configurations, all using an intra-cavity lens to compensate for thermal lensing in the Tm:YAP crystal. Q-switched lasers incorportating a Cr:ZnS saturable absorber (SA), resonant mechanical mirror scanner, or acousto-optic modulator were characterized. To enable higher average output powers, measurements of the thermal lens were conducted for the Tm:YAP crystal as a function of pump power and were compared to values predicted by a finiteelement- analysis (FEA) thermal-optical model of the Tm:YAP crystal. A resonator model is developed to incorporate this calculated thermal lens and its effect on laser performance. This paper will address approaches for improving the performance of Tm:YAP lasers, and means for achieving increased average output powers while maintaining high optical efficiency for both SA and mechanical Q-switching.

We describe mid-IR sources utilizing ZGP and CSP Optical Parametric Oscillators (OPO) directly pumped by high efficiency 1.94 μm Tm:YAP Q-switched lasers. Compact Q-switched Tm:YAP lasers, implemented using Cr:ZnS saturable absorbers, generated 29 kW peak power pulses and an average power of 4W. The OPOs, constructed using the latest generation ZGP and CSP crystals with low 1.94 μm absorption, were operated at near-degeneracy with mid-IR output in the 3.6-4.2 μm range. Various doubly-resonant OPO configurations were evaluated, including single-pass pump pass and double-pass pumping. Maximum mid-IR powers of 2.3 W and 2.5 W and optical conversion efficiencies of 58% and 64% were measured for ZGP and CSP double-pass pump OPOs, respectively.

We describe and compare the performance of two types of compact, passively Q-switched Yb:YAG 1030nm lasers and their use for 257nm fourth harmonic generation (FHG). In the first implementation, an end-pumped Yb:YAG laser produced a 250μJ pulse train with an average power at 1030nm of 3.6W. Using a 10mm LBO crystal (70% doubling efficiency), followed by a 7mm BBO crystal (45% conversion efficiency), 1.1W at 257nm was generated (overall FHG efficiency of 30%). The second implementation was a side-pumped Q-switched Yb:YAG laser pumped by a 200W diode bar. A 10mm KTP crystal followed by a 6mm BBO crystal resulted a 15% FHG conversion efficiency. The UV emission was in a form of 1-5 Hz PRF, 2ms long burst of 0.2mJ pulses with a 30kHz intra-burst PRF. Within a 1.65ms emission window, an 11.5mJ burst at 257 nm was generated that had a maximum intra-burst power of 7W. This paper will address the merits of each approach for realizing a man-portable laser suitable for ultraviolet Raman explosives detection.

We describe compact and efficient Q-switched diode-pumped, Tm:YAP lasers operating at 1.94μm. Laser CW and Q-switched performance is compared, using both compact mechanical as well as passive Q-switching. For passive Q-switching using a Cr:ZnS saturable absorber (unsaturated transmission of 95%), the laser produced 0.5mJ pulses with an average power of 4.4W and 6.5kW peak power, and had an optical efficiency of 30%. A resonant mirror mechanical Q-switch resulted in a 4 kHz PRF pulse train, with an optical slope efficiency of 52% and an optical-to-optical conversion efficiency of 41%. The laser generated 1.5 mJ, 45 ns FWHM, 33kW peak power pulses, and 6.2W of average output. A second mechanically Q-switched laser operating at 10 kHz PRF produced 1mJ, 35kW peak power pulses, generating 11W average power with an optical efficiency of 46%, and a beam quality of 1.4x diffraction limit.

We present a compact, side pumped passively Q-switched Yb:YAG laser that was operated in a burst mode with pump durations of 2-4 ms at low duty cycles. Intra-pump pulse Q-switched pulse repetition frequencies varied from 5-20 kHz depending on the transmission of the Cr:YAG saturable absorber, which was varied from 70% to 94%. Pump duration, pulse repetition frequency and output coupler reflectivity were optimized to yield maximum Yb:YAG laser average power and laser efficiency, while providing sufficient peak intensity, typically 0.3-1 MW, to enable efficient forth harmonic generation (FHG). Pulse energies and durations were in ranges of 0.3-1.8 mJ and 1.5-7ns, respectively, dependent on the unbleached transmission of the Cr:YAG saturable absorber. We achieved an optical efficiency of greater than 15% for the Yb:YAG laser. Extra-cavity 515 nm second harmonic generation (SHG) was achieved using a 5mm long KTP crystal. The 515 nm light was then frequency doubled by focusing it into a 7mm long BBO crystal, resulting in a 15% conversion efficiency from 1030nm to 257.5 nm, with an average UV power greater than 100 mW.

We describe a compact, side-pumped, Er/Yb glass laser with a low cost mechanical Q-switch. The Q-switch uses a mirror or reflecting prism mounted on a cantilever resonant spring that is driven by a small electromagnetic coil. The demonstrated laser used a 5 mm long Er/Yb glass gain element, and was side-pumped by a 940 nm, 5 mm wide diode bar generating up to 100 W peak power. Target energies of 3mJ have been realized in a near-diffraction limited mode, with pulse widths of 15-25ns, and an optical-to-optical efficiency of greater than 2%. The mechanical Q-switch assembly was fully athermalized via mounting a displacing porro reflector to the cantilever spring, where a 2.5mJ laser was observed to operate with less than 5% variance over -35°C to+60°C.

A compact 1030nm fiber laser for ultraviolet generation at 257.5nm is presented. The laser employs a short length of highly-doped, large core (20μm), coiled polarization-maintaining ytterbium-doped double-clad fiber pumped by a wavelength-stabilized 975nm diode. It is passively Q-switched via a Cr 4+ :YAG saturable absorber and generates 2.4W at 1030nm in a 110μJ pulse train. Lithium triborate (LBO) and beta-barium borate (BBO) are used to achieve 325mW average power at the fourth harmonic. The laser's small form factor, narrow linewidth and modest power consumption are suitable for use in a man-portable ultraviolet Raman explosives detection system.

A compact scanning LADAR system based on a fiber-coupled, monostatic configuration which transmits (TX) and receives (RX) through the same aperture has been developed. A small piezo-electric stripe actuator was used to resonantly vibrate a fiber cantilever tip and scan the transmitted near-single-mode optical beam and the cladding mode receiving aperture. When compared to conventional bi-static systems with polygon, galvo, or Risley-prism beam scanners, the described system offers several advantages: the inherent alignment of the receiver field-of-view (FOV) relative to the TX beam angle, small size and weight, and power efficiency. Optical alignment of the system was maintained at all ranges since there is no parallax between the TX beam and the receiver FOV. A position-sensing detector (PSD) was used to sense the instantaneous fiber tip position. The Si PSD operated in a two-photon absorption mode to detect the transmitted 1.5 μm pulses. The prototype system collected 50,000 points per second with a 6° full scan angle and a 27 mm clear aperture/40 mm focal length TX/RX lens, had a range precision of 4.7 mm, and was operated at a maximum range of 26 m.

We describe a compact and efficient mid-infrared (mid-IR) source based on zinc germanium phosphide (ZGP) and cadmium silicon phosphide (CSP) optical parametric oscillators (OPOs), operating in near degenerate condition, directly pumped by a 1.94 μm thulium (Tm)-doped yttrium-aluminum-perovskite (YAP) laser. The Tm:YAP laser is passively Q-switched by a chromium-doped zinc sulfide saturable absorber, and is operated to 4 W average power with a peak power of 29 kW. The laser emission was used to pump CSP and ZGP doubly resonant linear OPO cavities, generating a maximum 3.5-4.2 μm mid-IR emission of 2.5 W for CSP and 2.3 W for ZGP, with maximum optical conversion efficiencies of 65% and 58%, respectively, achieved for the two OPO crystals.

We describe a compact, highly efficient, diode-pumped, mechanically Q-switched Tm:YAP laser operating near 2 μm. The Q-switch, based on a torsion spring resonant mirror scanner, had negligible optical loss and required very low electrical drive power. At a 10 kHz pulse repetition frequency, the laser generated an average output power of 10.5 W at 1.94 μm, Q-switched pulse energy of 1.05 mJ, a pulse length of 31 ns, and a peak power of 34 kW. The Q-switched laser exhibited maximum optical and electrical efficiencies of 51% and 26%, respectively.

A highly compact and low power consuming Q-switch module was developed based on a fast single-axis MEMS mirror, for use in eye-safe battery-powered laser range finders The module’s 1.6mm x 1.6mm mirror has

Using a resonant scanner mirror Q-switch to provide a time varying change in cavity alignment, 1535nm lasers based on Er/Yb-doped glass and 1064nm lasers based on Nd:YAG were evaluated. Using a side pumping architecture, the Er/Yb glass laser used a compact mechanical Q-switch with a mirror rotation rate of 330 Rad/s, enabling generation of

An all-fiber monostatic laser rangefinder, using a double cladding fiber to transmit and receive light through a single lens is described. Ranging to >50 m with 12 uJ, 8 ns, 1540 nm pulses is shown. The all-fiber system is compact and needs no precise receiver/transmitter beam alignment.

Quasi-phase-matched (QPM) materials allow the generation of spectroscopically useful infrared radiation in an efficient and broadly tunable format. Here, we describe several applications of QPM-based light sources to remote and local chemical sensing. The remote systems are gas imagers that employ a fiber-pumped continuous-wave optical parametric oscillator or a microlaser-pumped, diode-seeded optical parametric amplifier as the illumination source. Technology described for local sensing includes a cavity ring down spectrometer that employs a novel optical parametric generator–amplifier to achieve ≥350 cm-1 of contiguous tuning and a long-wave infrared light source based on QPM GaAs. In each case the use of QPM materials in conjunction with effective pump sources instills simplicity and ruggedness into the sensing systems.

We describe a diode-pumped, passively Q-switched 2 μm Tm:YAP laser generating 10.5 W of average power. The laser utilized a Crsup2+/sup:ZnS saturable absorber with a nonsaturated transmission (Tsub0/sub) of 90% and exhibited a record 46% optical slope efficiency and a 42% overall optical conversion efficiency, both measured relative to the incident 794 nm pump power. At maximum average output power, the laser generated 0.6 mJ Q-switched pulses with a maximum peak power of 32 kW. Pulse duration varied between 20 and 53 ns, depending on operating wavelength and pump power. A laser with a Tsub0/sub=80% saturable absorber generated 1.45 mJ Q-switched pulses with a peak power of 138 kW.

The authors review recent demonstrations of improved mid-IR laser performance when a type II ‘W-well’ structure is incorporated into the active region. The W configuration consists of a hole quantum well (e.g. GaSb or GaInSb) between electron quantum wells (e.g. InAs) in order to maximise the gain while suppressing nonradiative Auger losses. Optically pumped W lasers recently produced more than 1.4 W per facet peak power for pulsed operation at 300 K. An interband cascade laser with a W active region (W-ICL) has operated up to 286 K. The first III–V mid-IR VCSEL (λ = 2.9 µm) with a W active region has lased up to 280 K for pulsed operation and to 160 K for cw, with a cw threshold of only 4 mW for a 6 µm spot at 78 K.

A review of optical beamforming techniques is presented. The techniques are subdivided into two broad categories. First, several representative implementations of narrow band, phase-only techniques are summarized. A detailed description of a narrow band architecture realized in our laboratory is presented. The architecture is based on coherent heterodyning of two narrow linewidth Nd:YAG lasers, with a controlled angular beam offset to generate the required microwave phase progression. Second, several representative wideband, true time delay architectures are briefly described. A description of a 'dispersive-prism' based true time-delay technique developed in our laboratory is presented. The results show multi-octave one-dimensional transmit and receive true time-delay beamformer operation, as well as two-dimensional transmit beamformer operation.

We report optically pumped four-constituent InAs/InGaSb/InAs/AlSb type-II quantum-well lasers emitting at 3.2–4.1 μm. Lasing was observed up to 350K under pulsed operation, with a characteristic temperature T0 up to 68K at temperatures above ambient.

We have fabricated prototype frequency tripled Nd:YAG lasers using 808nm Vertical Cavity Surface emitting laser (VCSEL) arrays for end-pumping. The passively Q-switched Nd:YAG laser generated 15mJ pulses with a duration of 2-4 ns. Used as a source for third harmonic generation, the laser produced in excess of 2mJ at 355nm. Of particular concern was the impact of temperature variation on conversion efficiency, which included effects for both the source laser and non-linear crystals. Various solutions to the temperature effects were explored to enable operation of the frequency tripled laser over a wide temperature range.

Laser illumination makes it possible to perform high resolution imaging when ambient light level is insufficient to overcome camera noise. The relatively long coherence length of most lasers, however, causes coherent speckle in the camera image plane, which can result in a significant decrease of the image quality and the maximum achievable target identification range. We characterized several types of NIR and SWIR laser diode illumination sources, with emphasis placed on measuring the properties of coherent speckle observed in the camera image plane. Image plane speckle contrast was measured by illuminating the imaged Lambertian surface with single-mode laser, multi-mode laser, wide-stripe laser with two active junctions and broad-band emission, and NIR and SWIR vertical cavity surface emitting laser (VCSEL) arrays. The impact of various imaging system parameters, including pixel size, imaging lens focal length, F-number, and IFOV on the contrast and characteristic size of the speckle intensity distribution were determined. Speckle contrast dependence on the polarization properties of various reflecting surfaces was measured. The reduction of speckle contrast with increasing source spectral width, and increasing size of spatially incoherent VCSEL emitter arrays will be described. We show that a speckle contrast of 5-10% is achievable for a typical long range SWIR imaging system.

We describe generation of 1.1 W of 257 nm emission by frequency quadrupling the 1030 nm emission from a compact passively Q-switched Yb:YAG laser. The laser utilized a volume Bragg grating to achieve a 0.1 nm linewidth required for UV-Raman spectroscopic applications, generated 100 kW peak power, 250 μJ pulses and 3.6 W of average power at 1030 nm. Fourth harmonic generation (FHG) was carried out using a 10 mm lithium triborate (LBO) crystal to generate 515 nm second harmonic with 70% conversion efficiency, followed by a 7 mm beta-barium borate (BBO) crystal to generate 257 nm fourth harmonic with 45% efficiency, resulting in an overall nonlinear conversion efficiency of 31%. Far-field and near-field of the FHG emission were characterized.

During the past few years the Monoblock laser has become the laser-of-choice for Army laser range-finders. It is eyesafe with emission at 1570 nm, high pulse energy, simple construction, and high efficiency when pumped by a laserdiode stack, providing advantages that are not available with other laser types. Although the divergence of the Monoblock output beam is relatively large, it can be reduced to 2.5 X reduction from the unmodified laser. Performance using this technique with various feedback and etalon spacings will be presented. Laser diode array and VCSEL pumping were both investigated with similar results.

We have explored using 808nm Vertical Cavity Surface emitting laser (VCSEL) arrays for end-pumping of Nd:YAG lasers. A variety of laser designs were explored including a compact passively Q-switched lasers that produced a 22mJ pulse having a pulse width of

The stability of a plane wave propagating in single- and double-pass broad-area diode laser amplifiers is analyzed. It is found that laterally periodic perturbations exhibit a longitudinal variation that is a mixture of exponential growth and periodic oscillation. The latter oscillation has a spatial period related to the Talbot distance. Due to the interaction between these two effects, double-pass amplifiers become unstable against lateral perturbations, and the field spontaneously collapses into a periodic array of filaments. Experimental results are presented that show good agreement with the theoretical analysis. >

Measurements of absorption losses in KNbO3 and MgO‐doped KNbO3 were made in the blue and near‐infrared wavelength regions using laser calorimetry. In the doped samples, the absorption loss for blue light was found to be 40% lower than that of the undoped samples. An enhancement in the infrared loss, caused by the presence of blue light, was observed in doped and undoped samples, but found to be much greater in the MgO‐doped crystals. The blue‐enhanced infrared absorption was characterized using two‐wavelength laser calorimetry. Temporal variations in the second‐harmonic power, caused by nonuniform heating of the active volume by the absorbed infrared and second‐harmonic power, are described.

We have explored using UV illumination as a method to mitigate pyroelectric effects, and their associative loss in hold-off for lithium niobate Q-switch materials under cold temperature operation. It has been observed that by illumination of the LiNbO 3 Q-switch material from the side, the above bandgap light can provide for an increase in conductivity via an increase in photocarriers. In the presence of strong pyroelectric fields associated with a change in temperature, these carriers can be effectively swept in the direction to eliminate the field. We quantified the improvement in conduction by measuring the decay time for the pyroelectric induced loss in extinction. At negative 20°C, the decay rate for the pyroelectric field in the absence of UV illumination was measured to be 16.7 hours. It was found that by illuminating the LiNbO 3 from the side with two UV LEDs operating at 500mA, the decay constant for a built-up pyroelectric charge could be reduced to 1minute. With this technique applied to a LiNbO 3 Q-switched laser, the laser was shown to perform over rapid cooling without a degradation in performance.

The method of optical triggering using a brass board architecture for a Q-switched Nd:YAG laser by direct bleaching of a Cr:YAG saturable absorber was determined to be effective in reducing the pulse-to-pulse timing jitter. A miniaturized triggering setup was employed to enable the brass board operation of the optically triggered laser. A 3mm wide minilaser diode bar (1024nm) with collimated emission was mounted on a compact heat sink and used to bleach the Cr:YAG saturable absorber from a direction orthogonal to the lasing axis. A compact 300A pulse driver, with

A broad-area tapered-contact single-pass amplifier emitting at 860-nm wavelength is demonstrated to emit up to 5.25 W continuous wave (CW) in a near-diffraction-limited radiation pattern. The diffraction-limited component of the radiation pattern, comprising greater than 87% of the total power at 5.25-W CW output, is observed to decrease slightly with increasing drive current due to filament formation. The output beam astigmatism is found to saturate at high power output in accordance with gain saturation, which indicates that the high-quality output beam remains stable with respect to small changes in current or injected power. >

A high-power external-cavity ring laser, incorporating a 600- mu m-wide GaAlAs traveling wave amplifier as a gain element, is demonstrated. The laser generated a pulsed (200 ns) output power of 9.3 W with a near-diffraction-limited beam quality and unidirectional ring propagation. The power versus output coupling dependence agreed with independently measured gain saturation characteristics of the amplifier. >

A Mach-Zehnder imaging interferometric is used to directly measure the lateral phase profile in the near field of broad-area semiconductor optical amplifiers with lambda /25 phase resolution, or 0.1 degrees C in temperature. The quadratic thermally induced phase distortion and its equivalent thermal lens focal length are characterized. Anomalous localized phase variations are correlated to thermal bond nonuniformities in devices mounted under nonoptimal conditions. It is demonstrated for an unbiased 600- mu m-wide by 1000- mu m-long amplifier device that a phase uniformity across the stripe of better than lambda /25 can be obtained. >

Operating characteristics of high-power large-active-area GaAlAs amplifiers configured in double-pass and single-pass traveling-wave arrangements are described. Single-pass broad-area amplifiers with a 600- mu m stripe width generated up to 21 W of near-diffraction-limited emission under pulsed operation when injected with 500 mW from a Ti:Al/sub 2/O/sub 3/ laser, and 11.6 W when injected with 100 mW from a laser diode master laser. In CW operation, a broad-area amplifier output of 3.3 W was demonstrated. Tapered-stripe large-area amplifiers emitted up to 4.5 W in a near-diffraction-limited beam when injected with 150 mW from a Ti:Al/sub 2/O/sub 3/ laser. The physical mechanisms causing degradation of the output beam phase front and intensity uniformity at high output power levels, including thermal lensing and filamentation, are presented. >

The seven papers making up this assessment are based on the Workshop on Nonlinear Optical Materials held in April 1986.

Performance of a repetitively pulsed mode-locked Nd:glass laser system employing athermal phosphate glass in the oscillator and amplifier stages is described. Improved passive mode-locking characteristics of the oscillator are achieved through use of a l00-microm thick intracavity etalon, enabling reliable generation of transform-limited pulses typically of 5-psec duration. The system produces 1054-nm pulses of high beam quality and ~25-mJ energy at a pulse repetition rate of ~0.2 Hz. Subsequent frequency-doubling steps give conversion efficiencies of ~50% and 25%, respectively.

To address the issue of pulse-to-pulse timing jitter in a passively Q-switched Cr:YAG/Nd:YAG laser, we have developed a technique for optical triggering, where the energy from a single bar diode was used to bleach a thin sheet within the Cr:YAG saturable absorber from a direction orthogonal to the lasing axis. A strong anisotropy for bleaching effect was observed; with appropriate polarization of the bleaching light the transmission through the saturable absorber was increased from 45% to 63%. This technique was applied to a monolithic Cr:YAG/Nd:YAG laser operating under steady state conditions. By placing the Q-switched pulse at the time corresponding to the steepest slope for change in transmission during bleaching, which occurs ~1μs after the bleaching diode trigger, we measured an 12.5X reduction in the pulse-to-pulse timing jitter, from 100ns for free running operation to 8ns with optical triggering.

Tunable narrow-band cw difference-frequency generation at 8.7 microm was demonstrated in silver gallium selenide (AgGaSe(2)) at room temperature. The crystal was pumped by an injection-seeded Er/Yb-codoped fiber amplifier at 1.554 microm and a fiber-coupled diode-pumped monolithic ring Nd:YAG laser at 1.319 microm. The difference-frequency output was used for high-resolution spectroscopy of sulfur dioxide (SO(2)).

Optical triggering via direct bleaching of a Cr:YAG saturable absorber was applied to a monolithic Nd:YAG/Cr:YAG laser crystal. The method uses a single laser diode bar to bleach a thin sheet within the saturable absorber from a direction orthogonal to the lasing axis. By placing the Q-switch at the time corresponding to the steepest slope (dT/dt) for change in transmission during bleaching, the pulse-to-pulse timing jitter showed a 13.2x reduction in standard deviation, from 132 ns for free-running operation to 10 ns with optical triggering. We measured that a fluence of 60 kW/cm(2) was sufficient to enable optical triggering, where a diode appropriately sized for the length of the Cr:YAG (approximately 3 mm) would then require only approximately 150 W of optical power over a 1-2 micros duration to enable effective jitter reduction. Additionally, we measured an increase in optical-to-optical efficiency with optical triggering, where the efficiency improved from 12% to 13.5%.

We produced ultraviolet radiation by frequency tripling the mode-locked emission of an external cavity laser containing a tapered GaAlAs amplif ier gain element. The 429-nm second harmonic produced by a KNbO(3) crystal was sum-frequency mixed with the 858-nm fundamental in a Li(3)BO(5) crystal, generating as much as 50 microW of power at 286 nm.

A bulk, quasi-periodic phase-matched difference-frequency process is demonstrated in field-poled LiNbO(3). Continuous tunability of output radiation in the 3.0-4.1-microm wavelength range is achieved through grating rotation. A maximum mid-infrared output power of 0.5 mW is measured.

Tunable UV radiation near 215 nm was produced by frequency quadrupling the 860-nm emission of a mode-locked external-cavity compound semiconductor laser containing a tapered GaAlAs amplifier. A KNbO(3) crystal generated the 430-nm second harmonic, which was doubled by a beta-BaB(2)O(4) crystal, producing tunable UV radiation with as much as 15 microW of average power.