Performance of a continuous-wave forsterite laser with krypton ion,Ti:sapphire, and Nd:YAG pump lasers

The authors characterize continuous-wave operation of a chromium-doped forsterite (Cr⁴⁺:Mg₂SiO₄) laser using krypton ion, Ti:sapphire, and Nd:YAG lasers as pump sources. Measurements were made pumping at 647 nm and 676 nm with the krypton ion laser, between 690 and 1010 nm with the Ti:sapphire laser, and at 1.06 μm with the Nd:YAG laser. Threshold pump powers and slope efficiencies are compared for output coupler transmissions varying between 1 and 15.5%. Room-temperature operation was only achieved using the Nd:YAG pump laser. Forsterite laser output power as a function of both temperature and pumping wavelength is discussed     

Efficient gain-switched operation of a Tm-doped silica fiber laser

We present the results from experiments relating to a gain-switched Tm-doped silica fiber laser in which a gain-switched Nd:YAG laser is used to pump the ³H₅ energy level of the Tm³⁺ dopant ion. This fiber laser configuration is the first example to our knowledge of a moderate energy gain-switched fiber laser which is pumped with a low-repetition-rate high-energy pulsed laser. For a near-optimized cavity, the gain-switched fiber laser produces a maximum pulse energy of 1.46 mJ at a maximum linear slope efficiency of 20% and a total optical-to-optical efficiency (with respect to the launched energy) of 19%. At low pump energies, the slope efficiency is approximately 40%, however, saturation of the output pulse energy is observed with the increase in the launched pump energy. We also present results from a numerical model that simulates ³H ₅-band pumping and includes all of the known pump excited-state absorption (ESA) mechanisms and, in addition, four cross-relaxation mechanisms have also been included. The calculations establish that the pump ESA mechanism contributes only a small loss factor to the overall efficiency of the laser when the Tm-doped silica fiber laser is pumped at low pump energies, however, as the pump energy is increased, losses due to pump ESA limit the amount of output energy from the fiber laser. The loss mechanism is mainly attributed to pump ESA from the ³H₄ upper laser level to the combined ³F_2,3 energy level at low launched pump energies because of the large absorption cross section for this transition and the relatively long lifetime of the ³H₄ energy level. For harder pumping conditions, the majority of the excited state population resides in the ¹G₄ level, inhibiting in some laser configurations gain-switching of the fiber laser until cessation of the pump pulse itself     

Modeling and CW operation of a quasi-three-level 946 nm Nd: YAG laser

A model is developed for an end-pumped quasi-three-level laser with population in the lower laser level at equilibrium such as for transitions to the manifolds⁴I9/2in Nd³⁺,⁴I15/2in Er³⁺,⁵I8in Ho³⁺and³H6in Tm³⁺. It is shown that the effect of residual lower laser level population on laser operation can be treated as a saturable loss. Room temperature operation on the⁴F3/2-⁴I9/2transition in Nd:YAG under CW dye laser pumping has been demonstrated with a threshold as low as 11.5 mW incident power and a slope efficiency of 7 percent with 0.3 percent output coupling. Performance is limited by the low output coupling and diffraction loss.     

Investigation of efficient self-frequency-doubling Nd:YAB lasers

We report on the investigation of efficient self-frequency doubling Nd:YAl₃(BO₃)₄ (Nd:YAB) lasers. Pumped by 1.6 W of 807 nm diode laser radiation, the Nd:YAB laser generates a green 531-nm output of 225 mW which corresponds to a conversion of pump to visible output power of 14%. Conversion efficiencies as high as 20% could be achieved by using the diffraction-limited beam of a Ti:sapphire laser as pump source. In this case, 2.2 W of 807-nm Ti:sapphire radiation produced a 531-nm output of 450 mW. The experimental performance of these Nd:YAB lasers is in good agreement with the predictions of a numerical analysis based on rate equations adequate for lasers with self-frequency doubling     

High average and high peak brightness slab laser

A high average and high peak brightness Nd:YAG MOPA laser system composed of a laser-diode-pumped Nd:YAG master oscillator, flash-lamp-pumped slab power amplifiers and a phase conjugated mirror was developed. The system demonstrates an average output power of 235 W at a repetition rate of 320 Hz and a peak power of 30 MW at a pulse duration of 24 ns with M²=1.5. Both an average brightness of 7×10⁹ W/cm²·sr and a peak brightness of 1×10¹⁵ W/cm2·sr are achieved simultaneously. The system design rules that we confirmed suggest that by replacing lamp pumping in the amplifier with laser-diode pumping, an average output power of ~1 kW can be obtained at ~1 kHz with a higher average brightness of ~3×10¹⁰ W/cm²·sr and a higher peak brightness of ~3×10¹⁵ W/cm²·sr     

Efficient laser emission in concentrated Nd laser materials underpumping into the emitting level

The possibility of using concentrated Nd laser materials for efficient laser emission and for scaling to high powers is discussed. It is shown that the increased optical absorption in these materials makes direct pumping into the emitting level feasible, with a reduction of the quantum defect between the pump and emission wavelengths, which in turn can enhance the laser emission characteristics and reduce heat generation under pumping. The investigation of the effect of Nd concentration on emission decay of Nd:YAG indicates that up to quite high concentrations, the reduction of the emission quantum efficiency by self-quenching can be compensated by an increase in the pump absorption. Efficient continuous-wave laser emission is demonstrated under direct pumping into the ⁴F_3/2 emitting level of Nd:YAG crystals with up to 3.5-at.% Nd, Nd:YAG ceramics with up to 6.8-at.% Nd, and Nd:YVO₄ crystals with up to 3-at.% Nd. Superior performance as compared to traditional pumping into the ⁴F _5/2 state were obtained. It is inferred that direct pumping into the emitting level of concentrated Nd materials can improve the efficiency of solid-state lasers in the free-generation or low-storage regimes and opens the possibility of scaling these lasers to high powers     

A diode-pumped 1.4-W Tm3+:GdVO4 microchiplaser at 1.9 μm

GdVO₄ as a host for thulium has several advantages for diode pumping in comparison with other crystals. The absorption cross section of thulium in GdVO₄ is considerably stronger and broader than in YAG and YLF, and the spectrum is shifted closer to the emission wavelength of commercially available AlGaAs laser diodes. In our paper, we report on a diode-pumped monolithic Tm³⁺(6.9 at.%):GdVO₄ microchip laser at 1.9 μm. A maximum output power of 1.4 W is achieved. Two different arrangements for cooling the crystal are discussed. Furthermore, the input-output curves under Ti:sapphire pumping are compared for different pump wavelengths. Slope efficiencies of 58%, clearly exceeding the Stokes limit of 41%, are achieved     

Energy storage and heating measurements in flashlamp-pumpedCr:Nd:GSGG and Nd:YAG

The authors have experimentally measured the energy stored and the heat generated in flashlamp-pumped Cr:Nd:GSGG for three Cr³⁺ concentrations in the range of 1-2×10²⁰ ions/cm³ . It has been found that the energy storage efficiency in these samples is 1.7 times greater than that of the Nd:YAG sample, and the normalized heating parameter χ, defined as the heat deposited per unit of stored energy, is 2.5 under the specified pumping conditions, with no evident dependence on the Cr³⁺ concentration. It has been been found that the measured χ value for the sample of Nd:YAG is 2.9 for the same pumping conditions. These observed χ values exceed expected values by factors of ~1.1 and 2 for the Cr:Nd:GSGG and Nd:YAG samples, respectively. The thermal focal length in the two materials was measured showing that the lensing is shorter in GSGG by a factor of 2.6 for the same available output power, or a factor of 4.5 for the same input pump power. The expected thermal lensing was determined using measured heat loads with no adjustable parameters, achieving satisfactory agreement with measured lensing values     

可调谐脉冲钛宝石光纤激光器

报道了用脉冲调Ｑ－Ｎｄ：ＹＡＧ激光器倍频泵浦的掺钛宝石光纤激光器。在一根φ３５０μｍ×１１．２ｍｍ的光纤中获得了０．５ｍＪ的泵浦阈值、１５μＪ的输出能量以及５６．５ｎｍ的调谐范围。     

高掺杂浓度Nd∶YAG微片激光器获得高效激光输出

用温度梯度法成功地生长了高掺Nd∶YAG晶体(Nd掺杂浓度高达3at.%).采用脉冲和连续的钛宝石激光器作为抽运源,对掺杂浓度分别为2at.%和3at.%的Nd∶YAG晶体微片进行了激光实验,获得了高效的激光输出.     

Photon avalanche upconversion in Er3+:YAlO3

The results of an investigation of photon avalanche upconversion pumping in Er³⁺:TiAlO₃ are reported. Five pump wavelengths corresponding to transitions from the metastable ⁴I_13/2 state to the ²H_11/2 state generated upconversion laser emission at 549.8 nm. The dependence of the laser output power on pump power near laser threshold is discussed in terms of a four-level kinetics model and is shown to reflect the threshold power requirement for photon avalanche. The maximum output power at 7 K was 33 mW, giving an optical conversion efficiency of 3.5% and a conversion efficiency of 28% based on absorbed power. Pumping Er:YALO by cross relaxation energy transfer produced 166 mW of laser output with an optical conversion efficiency of 17%     

Intracavity 1.549-μm pumped 1.634-μm Er:YAG lasers at 300 K

A novel method of generating 1.634-μm laser action from Er:YAG crystals pumped intracavity by an Er:glass laser emitting at 1.549 μm is described. Operation of the Er:glass laser at 1.549 μm (red shifted from the standard 1.532 μm, but with comparable output) at 500 K was obtained using mirrors with tailored spectral reflectivities. Several Er:YAG crystals ranging in concentration from 0.3% to 2% and in length from 1 cm to 8 cm were lased in the intracavity pumping arrangement. All the Er:YAG crystals lased in the ⁴I_13/2 :Y1(6544 cm^-1)-⁴I_15/2:Z6(424 cm ^-1) 1.634-μm transition at 300 K     

Efficient 2-$mu$m Continuous-Wave Laser Oscillation of Tm$^3 + $:KLu(WO$_4$)$_2$

Monoclinic crystals of Tm-doped KLu(WO₄)₂ were grown with high crystalline quality for several dopant concentrations. The relevant spectroscopic properties for the ³ F₄rarr³H₆ laser transition (cross sections, lifetime) were measured at room temperature. Laser oscillation in the 2-mum range was obtained both with Ti:sapphire and diode laser pumping near 800 nm using different setups. The maximum output powers achieved were 1.4 and 4 W, respectively, and the corresponding slope efficiencies with respect to the absorbed power were 60% and 69%, respectively. The novel monoclinic double tungstate thulium host KLu(WO₄)₂ was directly compared to KGd(WO₄)₂ and exhibited superior performance. The two laser polarization configurations for Tm:KLu(WO₄)₂ ,E//N_m and E//N_p, were also compared under identical conditions with pumping by the polarized Ti:sapphire laser. Tuning was studied for both of them using an intracavity Lyot filter and the tuning range achieved was from 1800 to 1987 nm. In the case of no polarization selective cavity elements the diode-pumped Tm:KLu(WO₄ )₂ laser naturally selected the E//N_m polarization     

Characterization of radiative and nonradiative Processes in Nd:YAG lasers by comparing direct and band pumping

Heat generation and laser performance of Nd:YAG oscillators pumped in two regimes, band pumping at /spl sim/808 nm and "thermally boosted" (TB) pumping at 884.5 nm, are compared. The crystal, pumped with a Ti:sapphire laser, lased with slope efficiencies of 52% and 57% when pumped at 802 and 884.5 nm, respectively. The heat generated during lasing was found to be 27% lower with TB pumping as compared to traditional band pumping. Moreover, the experimental results suggest that the coupling efficiency between the pump band and the upper lasing level (the quantum efficiency) is unity, and about 8% of the upper lasing level population decays via nonradiative channels.     

Laser diode-pumped holmium-doped fluorozirconate glass fiber laserin the green (λ~544-549 nm): power conversion efficiency, pumpacceptance bandwidth, and excited-state kinetics

The green (544-549 nm) Ho-doped fluorozirconate (ZBLAN) glass fiber laser, pumped in the red (λ~6;15 nm) by a high-power (~30 mW) InGaAlP laser diode or a ring dye-laser, has been characterized with regard to power conversion efficiency, fiber core-diameter and length, cavity output coupling, and pump acceptance bandwidth. Fibers doped with ~1200 ppm (by weight) of Ho and having core diameters of 1.7, 3, and 11 μm, and lengths ranging from 12.5 to 86 cm, have been studied in Fabry-Perot resonators having output couplings ranging from 1.545 to 96%. For a 1.7-μm core-diameter fiber, 21 cm in length, the threshold-launched pump power for the diode-pumped fiber laser is 1.9 and 3.5 mW for cavity output couplings of 1.5% and 24%, respectively. These values are the lowest for any upconversion-pumped fiber laser reported to date. Also, the noise and threshold-pumping power properties of the diode-pumped fiber laser are superior to those for its dye-laser-pumped counterpart. The highest laser slope efficiency (>22% with respect to launched pump power) was measured for a 3-μm core-diameter fiber and a cavity output coupling of 24%. The spectral interval over which the launched threshold pump power for this laser is <10 mW is almost 20 nm (637-656 nm). Studies of the fiber laser waveform as a function of pump power reveal competition for population between the ⁵S² and ⁵F₄ states and among the Stark sublevels of the ⁵F₄ manifold. Also, measurements of the output power on individual laser lines of the ⁵F₄, ⁵S₂→ ⁵I₈ (ground) transitions of Ho³⁺:ZBLAN as a function of pump power demonstrate the existence of a loss mechanism at the fiber laser wavelength, presumably due to absorption from ground or the ⁵I_y, ⁶S₂ or ⁵F₄ excited states of the ion     

Characterization and control of gamma and proton radiation effectson the performance of Nd:YAG and Nd:YLF lasers

The laser performance of Nd:YAG and Nd:YLF crystals longitudinally pumped at 800 mm was evaluated before and after exposure to ⁶⁰Co gamma rays and high energy (30-50 MeV) protons. Both forms of radiation created the same damage centers in the respective crystals, which reduced optimal output primarily by absorbing the laser emission. While the radiation induced loss at the lasing wavelength for high quality Nd:YAG reached a limiting value of ~0.015 cm^-1 at 100 krad exposure levels, the loss in Nd:YLF was significantly larger than in Nd:YAG for all comparable dosage levels, and did not appear to have a limiting value. Given the relatively short path lengths of the laser crystals that were tested, the loss could be overcome for both materials under pulse-pumped operation, demonstrating that certain Nd lasers can be effectively radiation hard by design. Additionally, for the first time, Cr³⁺ was codoped with Nd in YAG (with minimal Cr⁴⁺ formation) yielding a high performance material with a significantly reduced radiation susceptibility     

An InGaAs/GaAs SQW laser integrated with a surface-emittingharmonic generator for DWDM applications

An In_0.22Ga_0.78As/GaAs single quantum-well (SQW) laser integrated monolithically with a surface-emitting harmonic generator (SEHG) segment was fabricated and tested. By coupling a 1.06-μm Nd:YAG laser output into the active device, the green surface-emitting light at 0.51 μm was observed as the result of nonlinear interactions within the SEHG segment. The nonlinear interaction cross section A^nl of the device was found to be 2.3×10^-7 W^-1, which agrees well with theory. The application of the active devices as a dense wavelength-division-multiplexing (DWDM) demultiplexer was demonstrated with a tunable Ti:sapphire laser to simulate the multiwavelength signal source and a CCD detector array to record the spatially separated signals of different wavelength. System resolution better than 2 nm was obtained for the device, which was limited by the short length of the SEHG segment. Potential for a DWDM channel spacing of 10 GHz is discussed     

高功率准连续掺钛蓝宝石激光器的数值模拟和实验研究

研制了一台用声光Ｑ开关内腔倍频Ｎｄ：ＹＡＧ激光泵浦的掺钛蓝宝石激光器，其最大平均输出功率达７．７１Ｗ。７．４Ｗ时的转换效率为３３％。通过数值模拟研究了该激光器的工作特性，其结果与实验基本相符。     

纳秒级窄线宽脉冲钛宝石激光注入BBO晶体光参量放大器

实验上采用纳秒级窄线宽脉冲钛宝石激光注入BBO光参量放大器 (BBO OPA) ,实现了一台纳秒级Nd∶YAG激光器作钛宝石激光器和BBO光参量激光器抽运源的高效率系统。获得了钛宝石激光作为信号光注入BBO OPA时其输出能量为无信号光注入时的 6倍 ,并实现了 5 70～ 6 70nm的连续可调谐窄线宽 (<0 1nm)参量激光输出     

Characteristics and kinetics of laser-pumped Ti:sapphireoscillators

The experimental performance of a gain-switched Ti:sapphire laser oscillator pumped by a frequency-doubled Q-switched Nd:YAG laser system is presented for a variety of operating conditions. A theoretical model developed for this oscillator predicts well its performance. The observed curved input-output energy plots for the oscillator result from the kinetics of gain switching and fluorescence decay during the gain buildup period. Fluorescence decay also produces observed oscillator thresholds higher than those normally predicted by the standard gain-equals-loss condition. Gain-switched parasitic modes, with a higher threshold but shorter round-trip time than the resonator mode, cause the resonator mode to oscillate only over a finite range of pump energies. Spectroscopic investigations show that the Ti:sapphire cross-section spectrum is well fit by a Poisson distribution, giving a peak cross section of 3×10^-19 cm² for the π polarization