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We have measured and characterized, over a wide range of doping levels, the UV-near-IR (190-2000-nm) absorption properties of Ti:sapphire crystals. We find that the strengths of absorption centered around 400-450 and 268 nm depend on the square of the Ti3+ doping level, suggesting an origin from pairs of Ti3+ ions. In addition, we have identified an absorption feature below 210 nm due to Ti3+, rather than Ti4+ charge-transfer transitions. Finally, our data on 800-nm-peak, near-IR absorption shows a complex lineshape, with a lower limit set by Ti3+ pair absorption. Thus the maximum possible Figure-of-Merit for Ti:sapphire reduces as the doping level increases.

The development of higher-power InGaN-based diode lasers facilitates their application to optical pumping of Ti:sapphire lasers. Recent diode-pumping results highlight some unexpected behavior, specifically with 450-nm-wavelength devices. To better understand this we have measured and characterized, over a wide range of doping levels, the absorption properties of Ti:sapphire crystals. We find significant changes in the spectral shape of the pumping band in Ti:sapphire with increased doping, and explain the results in terms of absorption due to pairs of Ti3+ ions. Our subsequent discussion attempts to explain prior data, and also provides guidance on optimizing designs for InGaN-diode-pumped Ti:sapphire lasers.

We report on the development of an all-fiber, 68-kW-peak-power, 16-ps-pulse-width, narrow-bandwidth, linearly polarized, 1064-nm fiber laser suitable for high-power, picosecond-pulse-width, green-light generation. Our 1064-nm fiber laser delivered an average power of up to 110 W at a repetition of 100- MHz in a narrow bandwidth, with minimal nonlinear distortion. We developed a high-power, picosecond green source at 532 nm through use of single-pass frequency-doubling of our 1064-nm fiber laser in lithium triborate (LBO). Using a 15-mm long LBO crystal, we have generated 30 W of average power in the second harmonic with 73-W of fundamental average power, for a conversion efficiency of 41%.

We report here on the performance of a narrow-line, mid-IR source based on a PPLN-crystal optical parametric generator (OPG). The crystal was pumped by a pulsed, 20-MHz-rate, 1064-nm Yb:fiber-based source operating with 20- psec pulses. The OPG produced a broad spectrum between 2027 nm and 2239 nm. By placing a band-pass filter after the OPG we were able to select a 30-nm bandwidth output, and we achieved further line reduction (0.7 nm) and 4.5 mW of average power at 2039 nm, using a reflective Volume Bragg Grating (VBG). Devices such as piezo-controlled etalons can provide rapidly tunable, narrow-linewidth power from this system.

We present a scheme using beta-barium borate (BBO) crystal to maximize fourth-harmonic ultraviolet (UV) generation from high-power, kHz-range repetition rate Nd lasers by reducing thermal dephasing during the phase matching process. Thermal dephasing due to nonlinear absorption (NLA) induced by two-photon absorption of high peak power fourth-harmonic UV radiation is reduced by minimizing second- and fourth-harmonic beam overlap through tight elliptical focusing perpendicular to the walk-off plane, leading to multi-watt, kHz-range repetition rate UV generation in BBO crystal. With such beam shaping, nearly 5 W at 10 kHz of 262-nm UV radiation is generated using an 8-mm long BBO crystal. The results of our investigation show an efficient way of achieving multi-watt UV generation at kHz-range repetition rate.

We describe fundamental measurements of the properties of thulium (Tm)-doped silica and power scaling studies of fiber lasers based on the material. Data on the high-lying Tm:silica energy levels, the first taken to our knowledge, indicate that pumping at 790 nm is unlikely to lead to fiber darkening via multiphoton excitation. Measurement of the cross-relaxation dynamics produces an estimate that, at the doping levels used, as much as 80% of the decay of the Tm level pumped is due to cross relaxation. Using a fiber having a 25-mum-diameter, 0.08 numerical aperture (NA) core, we observed fiber laser efficiencies as high as 64.5% and output powers of 300 W (around 2040 nm) for 500 W of launched pump power, with a nearly diffraction-limited beam. At these efficiencies, the cross-relaxation process was producing 1.8 laser photons per pump photon. We generated 885 W from a multimode laser using a 35-mum, 0.2-NA core fiber and set a new record for Tm-doped fiber laser continuous-wave power.

The multipass slab (MPS) solid-state laser design is a diode-laser, side-pumped configuration that combines high efficiency with high beam quality. Because of a relatively low volumetric thermal loading, the MPS configuration can be used with a wide variety of laser crystals to operate at relatively high powers, and in this paper, we review the MPS lasers based on the materials Nd:YLF, Nd:YVO, Tm:YLF, Er:YLF, Yb:S-FAP, and Cr:LiSAF.

Materials grown by vapor phase techniques such as chemical vapor deposition or hydride vapor phase epitaxy (HVPE) often exhibit very low losses which are difficult to quantify by simple transmission measurements. The measurement of extremely low absorption coefficients can be carried out by laser calorimetric or thermal rise techniques, which determine the absorption coefficients by measuring the temperature increase caused by the absorbed laser radiation. We report here on results of measuring absorption coefficients of bulk HVPE-grown orientation-patterned GaAs (OP-GaAs) and GaP (OP-GaP) crystals using one of the methods of laser calorimetry, called transient calorimetry. In our setup, the sample under test is attached to a high-conductivity copper holder and placed in a vacuum chamber. A 2-micron cw laser beam is transmitted through the sample and the temperature rise in the sample is measured and, through the calorimeter calibration process, related to the power absorbed in the sample. The absorbed power, Pa, is a function of the total attenuation coefficient αtot , the length of the sample, and the laser power Po, defined as Pa = Po exp (-αtot l), where total attenuation αtot is the sum of absorption and scattering: αtot = αabs + αscat. Since scattered light does not cause heating, the calorimetric technique is only applicable to determining αabs. By this technique we have measured 2-micron absorption coefficients in OP-GaAs and OP-GaP as low as 0.007 cm-1.

We have developed a quasi-CW, deep ultraviolet source producing >250 mW of 205-nm radiation. The source consists of a 100-MHz, mode-locked, 15-W, 1047-nm master-oscillator/power-amplifier, a synchronously pumped optical parametric oscillator, and three nonlinear conversion stages.

We review some recent developments in semiconductor and solid state lasers that facilitate major improvements in biomedical imaging systems. Examples include fiber-laser based ultrafast systems, and swept-frequency sources. Article not available.

We have operated, for the first time to our knowledge, a directly diode-pumped Cr:ZnSe femtosecond oscillator. In addition, we have constructed a CPA Cr:ZnSe-based ultrafast laser system that generates 2475-nm, 1-kHz-rate, 1 GW -peak-power pulses.

Reported near-diffraction-limited, cw power levels from Tm-doped silica fiber lasers in the 2000-nm wavelength region have now passed the 1 kW level, due to advances in fiber technology, pump lasers and associated pump-coupling fiber optics. Compared to the more common high-power Yb-doped fibers, Tm:silica fibers have several advantages, particularly with respect to limits set by fiber nonlinear effects such as stimulated Brillouin scattering. These have been exploited to allow generation of 600 W of single-frequency, narrow-linewidth power, the most, to our knowledge, of any fiber-based laser. In addition, there have been significant advances in generation of high-peak-power pulses from Tm:fiber-based sources.

We report the first, to our knowledge, femtosecond, oscillator, chirped-pulse, regenerative-amplifier system based Cr:ZnSe. To date, we have generated, at a 1-kHz rate, 0.3-mJ, 300-fs pulses (1 GW peak power) centered at 2475 nm.

We review the use of Ti:sapphire lasers to produce blue laser sources with particular emphasis on wavelengths useful for underwater communications. We discuss past designs as well as future prospects.

Pump wavelengths of less than 460nm compromise the performance of Ti:sapphire lasers by inducing loss. This – and not pump brightness or absorption – is the primary performance limitation in these lasers.

Thermal dephasing due to two-photon absorption-induced linear absorption is reduced by minimizing second- and fourth-harmonic beam overlap through tight elliptical focusing perpendicular to the walk-off plane, leading to multi-watt, high-repetition rate ultraviolet generation in BBO.

We report a 0.8-5.0 ns-width, 0.1-2 MHz-rate Nd-MOPA laser passively Q-switched with a semiconductor saturable Bragg reflector producing 7.5 W of average power at 532 nm in a diffraction limited beam.

We report 62% and 56% SHG conversion efficiency in generating 532-nm using MgO-doped and undoped PPSLT crystals, respectively. We compare SHG obtained using both materials and discuss their suitability for the generation of Watt-level green-radiation.

2-mJ, 600-fs, 1047-nm pulses at a 250-Hz rate from a compact, Yb -doped crystal CPA laser system were achieved. We combine a positive-dispersion-regime oscillator, regenerative amplifier and a hybrid stretcher/compressor based on chirped volume Bragg gratings.

A high-power, actively modelocked, cryogenically cooled Yb:YAG laser has been demonstrated. At a repetition rate of 80 MHz, 214-ps pulses with 55 W of output power have been measured.

Over 600 mW has been obtained from a single-frequency Nd:YAG ring laser pumped by two 1-W diode lasers. Tuning over 60 GHz in less than 5 ms was achieved with a galvanometer-controlled intracavity etalon. Locking to an external reference cavity has also been demonstrated. >

We report the development of a tunable, diode-pumped Cr:LiSrAlF 6 ring laser that emits as much as 43 mW of power in a single longitudinal mode at 849 nm. By tuning the output with a birefringent filter, we achieved single-frequency operation from 810 to 860 nm. The short-term (10-s) frequency stability was better than 15 MHz.

We have generated output energies of 900 mJ at 2050 nm from a pulsed, room-temperature, normal-mode Co:MgF(2) laser, with average powers as high as 6.5 W. Over the range 1800 to 2450 nm we have obtained pulse energies of at least 100 mJ.

A binary grating has been used to achieve coherent summation of diode-laser-pumped Nd:YAG ring lasers operating at 1.06 μm. Mutual coherence of two such devices was achieved by optical injection locking. This is believed to be the first demonstration of cw injection locking of solid-state lasers other than semiconductor diode lasers. By combining two beams, an efficiency of 75% (92% of the theoretical limit) has been demonstrated in a configuration that could be used to combine a large number of individual lasers.

Tunable, mode-locked operation of cw Co:MgF(2) and Ni:MgF(2) lasers has been demonstrated for the first reported time, and autocorrelation measurements of the pulse widths have been made. The Co:MgF(2) system has generated stable pulses over wavelengths from 1.65 to 2.01 microm and has produced pulses as short as 34 psec. The Ni:MgF(2) laser has operated over the 1.61-1.73-microm range, with pulses as short as 23 psec.

We assign the 2v(3) ? v(3) absorption transitions seen in a double-resonance pump-probe experiment. We compare the observed frequencies with those derived by calculating the 2v(3) rovibrational energy levels, using spectroscopic constants resulting from a 3v(3) analysis. Some features in the multiple-photon v(3) absorption spectrum of SF(6) can be attributed to two-photon transitions to 2v(3).

We have developed a compact, efficient, passively Q-switched, solid-state-laser, producing 7-mJ, < 10 ns pulses, and a near TEM00 beam. The cross section of the laser crystal was D-shaped and it was side pumped.

The fabrication of thick orientation-patterned GaAs (OP-GaAs) films is reported using a two-step process where an OP-GaAs template with the desired crystal domain pattern was prepared by wafer fusion bonding and then a thick film was grown over the template by low pressure hydride vapor phase epitaxy (HVPE). The OP template was fabricated using molecular beam epitaxy (MBE) followed by thermocompression wafer fusion, substrate removal, and lithographic patterning. On-axis (100) GaAs substrates were utilized for fabricating the template. An approximately 350 μm thick OP-GaAs film was grown on the template at an average rate of ~70 μm/hr by HVPE. The antiphase domain boundaries were observed to propagate vertically and with no defects visible by Nomarski microscopy in stain-etched cross sections. The optical loss at ~2 μm wavelength over an 8 mm long OP-GaAs grating was measured to be no more than that of the semi-insulating GaAs substrate. This template fabrication process can provide more flexibility in arranging the orientation of the crystal domains compared to the Ge growth process and is scalable to quasi-phase-matching (QPM) devices operating from the IR to terahertz frequencies utilizing existing industrial foundries.

We discuss several classes of tunable solid state lasers, based on Yb-doped crystals, Tm-doped fibers and Cr:ZnSe crystals, and patterned semiconductor nonlinear materials, all of which show promise for applications to analytic sensors.

Non-linear absorption limits Nd:YAG fourth harmonic generation in Li2B4O7. By characterizing the non-linear absorption coefficient, we determined that it could be reduced by controlling the temperature and repetition rate.

Using noncritically phase-matched 1-cm(2) -aperture KTiOAsO(4) (KTA) crystals in an optical parametric oscillator (OPO), we have demonstrated a sustained average signal power of 33 W at 1534.7 nm. To our knowledge, this is the highest-average-power signal ever generated by an OPO. The pump source was a 100-Hz Q -switched 1064-nm Nd:YAG laser. Compared with that of the similar and more-common material KTiOPO>(4) , idler absorption in KTA is negligible, allowing high-power operation with minimal thermally induced refractive distortion in the OPO crystal.

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.

We report on a Tm-doped silica fiber laser that generates 263 W of cw power with a launched pump conversion efficiency of 52% and a slope efficiency of 59%.

Q-Peak has been developing solid state laser and nonlinear optical systems applied to remote sensing for nearly 20 years. Our first devices were based on the use of gas-discharge lamps to optically pump the laser crystals, a standard technology that traces back to 1960 with the first laser demonstration, using ruby (Cr3+:Al2O3) as the laser material. In later and most current systems we have employed the newer and more efficient use of semiconductor diode lasers as pump sources, which has allowed operation at higher levels of performance and makes practical the deployment of satellite-based, active remote-sensing systems.

We report an efficient, TEM00, Tm:fiber-laser-pumped, Ho:YLF laser producing 43 W cw power and 45 mJ of pulse energy in the Q-switched regime, the highest values yet reported for this material.

A compact long-wavelength infrared (LWIR) source, based on the combination of a high-pulse-rate, 1-μm-wavelength solid-state laser with rapid and broadly tunable tandem optical parametric oscillators (OPOs) was demonstrated. Nanosecond pulses with up to 100 μJ energy, tunable within the 8-11 μm LWIR range were achieved.

In this paper we describe the design and performance characteristics of a diode-laser-pumped, cw, NdrYLF laser with intracavity second harmonic generation (SHG). We include descriptions of the micro-optics used to couple pump power from a 10-W diode laser to the Nd:YLF crystal in an end-pumped configuration; the opto-mechanical design of the Nd:YLF gain element; the performance of the Nd:YLF laser at 1047 nm; and the design and performance of resonators configured for intracavity SHG with both KTP (II) and LBO (I) crystals. The highest output power obtained to date, with an LBO SHG crystal, was 1.25 W at 523.5 nm.

We report a diode-pumped, Nd:YLF, Q-switched, short-pulse, 30-100-kHz MOPA system producing, to our knowledge, the highest third- and fourth-harmonic powers (25 and 10 W, respectively) yet reported for high-pulse-rate Nd-doped lasers.

This paper reports on the design and performance of a satellite-ranging transmitter consisting of a Cr:YAG passively Q-switched Nd:YAG microlaser and an air-cooled Nd:YVO4 power amplifier, generating 235-µJ, 270-ps pulses at a 2-kHz rate.

We have recently demonstrated efficient operation of KTP optical parametric oscillators (OPO) pumped by multimode Nd:YLF and Nd:YAG lasers. These experiments have demonstrated what is, to our knowledge, the highest pulse energy (450 mJ) and the highest average-power signal output (7.4 W) obtained to date from an OPO. With a 1.1-J, 10-Hz, Nd:YAG pump laser we obtained 450 mJ (4.5 W) of signal output at 1571 nm from a singly-resonant OPO. In a separate experiment with a 625-mJ, 30-Hz, Nd:YLF pump laser we obtained 7.4 W (245 mJ, 30 Hz) of signal output at 1550 nm. These results provide a clear demonstration that very high pump-to-signal energy conversion (up to 41%) can be obtained from an OPO even with highly multi-transverse-mode pump lasers.

We report on several developments in solid state lasers and nonlinear optics specifically for applications in remote sensing. In the area of UV sources for ozone monitoring, we have developed an efficient, third-harmonic, tunable Ti:sapphire-laser-based source. For long-range, eyesafe detection of aerosols, we report a high-energy optical parametric oscillator (OPO) driven by a flashlamp-pumped, Q-switched Nd:YLF laser. Finally, for mid-infrared DIAL, we have developed a Tandem-OPO that converts a common Nd-doped laser into a tunable source capable of providing wavelengths in the range 1500-5500 nm and 8000-12000 nm.

We report an energy of 110 mJ per pulse from a diode-pumped, double-pulse, Q-switched, conduction-cooled, 1053-nm, Nd:YLF laser designed for space-based applications. We obtained a slope efficiency of 23% and used heat pipes for laser-head cooling.

We report an efficient, TEM00, Tm:YLF-pumped Ho:YLF laser system producing 21 W CW power and 37 mJ of pulse energy in the Q-switched regime, the highest values yet reported for this material. A ZGP OPO pumped by the Ho:YLF laser produced pulse energies above 10 mJ at 50-400 Hz.

We report a 4-W, 2810-nm, diode-pumped, cw Er:YLF laser, to the best of our knowledge the highest power yet achieved for a cw Er-doped laser operating on the 4I11/2 - 4I13/2 transition. We tuned the laser on 11 different lines in the 2720-2840-nm region.

We report a diode side-pumped, single-stage, multi-pass Yb:S-FAP amplifier designed to achieve high pump brightness, uniform absorption, and high amplification. We demonstrate highly efficient operation of the amplifier with an input signal from a Nd:YLF oscillator.

A quasi-cw, deep ultraviolet source has been developed, producing >200 mW of 205-nm radiation. The source consists of a mode-locked 16-W 1047-nm master-oscillator/power- amplifier, a synchronously-pumped optical parametric oscillator, and three non-linear conversion stages.

We report on a broadly tunable (1905 - 2067 nm) diode-pumped Tm: YLF laser producing cw output powers of >18 W (37% slope efficiency) in multimode operation and 12 W in the TEM00 mode.