An intracavity 16-μm Raman laser: a theoretical investigation

A theoretical model describing the dynamics of an intracavity 16-μm laser was developed. This laser consists of a TEA-CO₂ laser with an intracavity Raman cell. The Raman medium could be either hydrogen or deuterium, depending on the required wavelength. Stokes, anti-Stokes, and pump coupling were considered. Output energies as well as pulse shapes were calculated. Optimum output coupling was also determined. The model predicted that the intracavity Raman laser could be a viable alternative to a conventional multipass Raman cell for generating intense 16-μm pulses     

Stimulated Raman shifting of the Nd:YAG fourth harmonic (266 nm) inH2, HD, and D2

The dependence of the first Stokes stimulated Raman conversion efficiency of fourth-harmonic radiation from a Nd:YAG laser at 266 nm has been studied for the isotopic species H₂, HD, and D₂ as a function of gas pressure and laser energy using a low numerical aperture (~4.5×10^-3) pumping geometry. While the laser energy threshold for first Stokes conversion is seen to vary significantly between the species it has been found that photon conversion efficiencies of at least 50% can be achieved for all of them for laser pump energies at 266 nm ⩽50 mJ/pulse. This study provides a new measurement of the differential cross section for stimulated Raman scattering in HD of 8.1±2.4×10^-29 cm²/sr at 266 nm and at high pressures, and agreement is found with previous measurements of the cross sections for H₂ and D₂. The results have been used to optimize the laser transmitter system for a differential absorption lidar (DIAL) system to measure tropospheric ozone concentration profiles     

Raman oscillation with intracavity sum-frequency generation

We use a plane-wave analysis to examine a Raman oscillator containing an intracavity sum-frequency interaction that frequency sums the circulating first-order Stokes radiation with the pump radiation. We find that there is an optimum ratio between the nonlinear coupling in the Raman medium and the nonlinear coupling in the sum-frequency generator. We also find that higher order Stokes radiation should be suppressed with the optimum choice of nonlinear coupling in the sum-frequency interaction. Numerical integration of the equations containing transverse effects predicts a time-averaged power-conversion efficiency of 61.4% for conversion of 532- to 273.5-nm radiation using a CW mode-locked frequency-doubled Nd:YAG laser with Ba(NO₂) ₃ for the Raman material and CsLiB₆O₁₀ (CLBO) for the sum-frequency material     

Stimulated rotational Raman conversion in H2, D2, and HD

Stimulated rotational Raman conversion has been efficiently demonstrated in all three molecular hydrogen isotopes with a 532-nm Q-switched pump source. Optimum gas pressures and pump focusing have been determined. Single pass conversion efficiencies of 80%, 75%, and 65% have been achieved at the first Stokes wavelengths with H₂ , D₂, and HD, respectively. The maximum efficiency is generally limited by further Raman conversion of the initially generated Stokes light. The thresholds were found to increase in the order H₂ 22. The relative thresholds of H₂ and D₂ are reasonably consistent with the calculated steady-state gains based on the population statistics and the linewidth data. Intermediate frequency shifts such as these may be useful by themselves, or in combination with other nonlinear techniques, as methods to achieve specific wavelengths for system applications     

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     

High-power narrow-band operation and Raman frequency conversion ofan electron-beam pumped krypton excimer laser

A Kr excimer laser pumped by a relativistic electron beam has generated high-power output by using a cavity composed of a Si mirror and M_gF₂ mirror. The threshold gas pressure for laser oscillation is 10 atm, and the maximum output power achieved so far is 6.6 MW at 15 atm. The maximum power is limited by the surface damages on the mirrors. This laser output, oscillating at 145.7 nm, has a spectral width of 0.8 nm (FWHM). Efficient spectral narrowing down to 0.1 nm has been achieved with a 32° apex angle MgF₂ prism inserted in the cavity giving 3.5 MW peak power at 15 atm of Kr gas pressure. Wavelength conversion by stimulated Raman scattering in high-pressure H₂ has been demonstrated for efficient extension of the laser wavelength     

Diode-pumped LiIO3 intracavity Raman lasers

We report on an all-solid-state intracavity Raman laser source operating at 1155 nm. The Raman-active medium is crystalline LiIO₃ , which converts emission at 1064 nm from Nd:YAG to the first Strokes wavelength of 1155 nm. We discuss the key design principles for this Raman laser and present its operating characteristics, including output power, efficiency, and spectral, spatial, and temporal properties     

低频移拉曼模式多阶级联的1.7 μm激光器

基于固体介质的拉曼频率变换是产生新波段激光的有效技术方案。利用1572 nm KTP光参量振荡器腔内泵浦KGW晶体,实现了1616 nm （2阶）、1638 nm （3阶）、1662 nm （4阶）、1686 nm （5阶）、1711 nm （6阶）拉曼激光输出,其中1711 nm占据主导地位。激光器最大总平均输出功率为1.13 W,最小脉冲宽度为20 ns。该多阶级联拉曼变频对应的单阶平均拉曼频移为86 cm?1,与文献报道的KGW晶体低频拉曼模式相吻合。采用1572 nm KTP光参量振荡器作为拉曼激光器的腔内泵浦源有两个优势,一方面可以有效拓展拉曼变频的输出波长,另一方面可以基于光参量振荡器的脉冲窄化特性为后续多阶拉曼转换提供高强度的泵浦光。通过引入多阶级联拉曼变频的方案,为有效利用固体介质非常规低频移拉曼模式提供了新思路。     

Tunable laser pumped 3 μm Ho:YAlO3 laser

The tuning characteristics of the ⁵I₆ -⁵I₇ transition in a Ho:YAlO₃ laser, intracavity pumped by a 1.079 μm Nd:YalO₃ laser, were studied. Operation on seven distinct lines between 2.844 and 3.017 μm was found, and the threshold and relative slope efficiency of each line was measured. Several of these lines were previously unreported     

VUV generation by high-order CARS

Generation of VUV (vacuum ultraviolet) radiation by stimulated Raman scattering (SRS) in H₂ is studied with collinear irradiation of the first Stokes component simultaneously with pump laser radiation. Improvements of the high-order coherent anti-Stokes Raman scattering (CARS) method over the pure SRS scheme are: generation of higher anti-Stokes (AS) orders, increased conversion efficiency, and considerably better reproducibility. Experimental results are presented to confirm the theoretical analysis     

High-efficiency pulse compression with intracavity Raman amplifiers

High-efficiency pulse compression using intracavity Raman amplifiers has been computed. The energy of a pump laser stored in a lossless cavity is extracted at the Stokes frequency by means of Raman amplification of an input Stokes pulse. Calculations are made for both long and short duration input Stokes pulses for different lossless cavities. As an example, we use a hydrogen-argon mixture as the Raman medium and 1.5 J/cm²energy fluence stored in the lossless cavity at the ruby frequency. By comparing amplified Stokes pulses to a 30 ns pulse duration conventional ruby laser delivering the same energy fluence, pulse shortening factors larger than 20 are computed with quantum conversion efficiencies higher than 80 percent. These values compare favorably to backward Raman amplification. Moreover, this technique is proved to be able to provide a pulse compression rate larger than 14, even for a broad-band laser, which is impossible with backward Raman amplification. This technique could be used with any laser, even with absorbing laser media (excimer lasers) provided pump energy is stored in the lossless cavity by shifting of the laser frequency with any nonlinear process.     

Transient dynamics of CW intracavity singly resonant opticalparametric oscillators

We study the transient dynamics of CW intracavity, singly-resonant optical parametric oscillators (ICSROs). Relaxation oscillations of the 1064-nm pump light are measured, in both the presence and absence of parametric conversion, in a periodically poled LiNbO₃ (PPLN) CW ICSRO pumped intracavity to a Nd:YVO₄ laser. The presence of parametric conversion is shown to significantly increase both the damping times and oscillation frequencies of the dynamics; at three times the parametric oscillator threshold, these take values of 200 μs and 2 MHz, respectively. Oscillation frequencies are shown to be in good agreement with theoretical values. The influence of energy diffusion and thermal lensing are analyzed to account for discrepences between measured and theoretical damping times. We discuss the implications of the dynamic behavior to the stable-power operation of CW ICSROs     

Theoretical characterization of Raman oscillation with intracavitypumping of fiber lasers

Theoretical results relating to the generation of continuous-wave (CW) output from fiber lasers that are internally pumped with light generated from the stimulated Raman effect are presented. This investigation establishes the important fiber and resonator parameters, such as the fiber length and glass composition, dopant concentration, and pump power required to realize this new form of fiber laser arrangement. Three examples are studied: the Ho³⁺-doped silica fiber laser that is pumped at a wavelength of 1.15 μm, the Er ³⁺-doped silica fiber laser which is pumped at 1.48 μm and, the Tm³⁺-doped silica fiber laser which Is pumped at 1.625 μm. These three examples cover first Stokes pumping, second Stokes pumping, and first Stokes pumping with direct dopant absorption of the pump light, respectively. The simulations involve the use of simple numerical models comprising the spatially dependent field propagation equations (under the slowly varying field approximation) and the rate equations for the population densities. It is established that intracavity Raman pumping of fiber lasers with first Stokes radiation is efficient when the losses at the pump, Stokes and laser wavelengths are kept low (<10 dB/km). It is also established that second Stokes pumping is, even with direct absorption of the pump light, theoretically quite efficient and, as a result, the Er³⁺-doped silica fiber laser which is pumped with second Stokes radiation at 1.48 μm may provide the best demonstration of intracavity Raman pumping     

The effect of the geometry of the active medium on the performanceof SF6+H2 pumped HF laser

Experimental study of a pulsed, electric-discharge-initiated, SF ₆+H₂ pumped HF chemical laser is presented. The reactants were premixed and the laser medium was preionized by means of a plasma cathode. The laser pulse energy, as a function of the discharge voltage, was measured for various laser medium parameters. It was concluded that the ratio between the width and height of the active volume is an important issue in the laser performance     

H2+和D2+谐波强度与波长的关系

为了了解H₂+及其同位素分子谐波光谱效率与激光波长之间的关系,采用求解2维薛定谔方程的方法,理论研究了600nm~1600nm激光波长下H₂+和D₂+谐波光谱强度随波长的变化关系。结果表明,光谱强度随波长增大而减小;在短波长区间,H₂+光谱强度减小的倍率要大于D₂+,在长波长区间,H₂+光谱强度减小的倍率要小于D₂+;此外,在弱光强下,H₂+光谱强度总是大于D₂+, 在强光强下,H₂+光谱强度在短波长区间小于D₂+, 而其在长波长区间大于D₂+; 核间距延伸和电荷共振增强电离在H₂+和D₂+谐波光谱强度变化上起到主要作用。这一结果对分子谐波调控是有帮助的。     

Stimulated Raman scattering of XeF* laser radiation in H2--Part II

Stimulated Raman scattering (SRS) experiments in hydrogen have been performed with a collimated beam from ane-beam pumped XeF laser operating at 353 nm. An unstable resonator provided good beam quality at energies of about 1.2 J and pulse lengths of about 320 ns. A folded-path Raman cell allowed cell lengths to be continuously varied up to 11 m at a hydrogen pressure of 10 atm. Energy conversion efficiencies of >45 percent to first Stokes (S1) at 414 nm and >40 percent to second Stokes (S2) at 500 nm were observed with no indication of significant four-wave processes.     

Dependence of rotational and vibrational Raman scattering onfocusing geometry

Stimulated rotational and vibrational Raman scattering in H₂ was investigated with a circularly and a linearly polarized XeCl laser beam and the influence of the focusing geometry on the threshold for rotational and vibrational scattering, respectively, was studied. It is shown that with a circularly polarized pump beam a high-angle focusing geometry allows to get only rotational Raman scattering, whereas a low-angle focusing geometry provides only vibrational Raman scattering for gain suppression effects     

LD抽运被动调Q Nd:YAG/GdV04内腔式喇曼激光器

为了研究LD抽运的被动调Q Nd:YAG/GdVO4内腔式喇曼激光器的输出特性,采用Nd:YAG作为激光介质,GdV04晶体作为喇曼介质,分别用两块不同初始透过率的Cr<'4+>:YAG晶体,得到并比较了采用不同初始透过率的Cr<'4+>:YAG晶体时被动调Q喇曼激光器的性能.测量了平均输出功率、脉冲宽度和脉冲重复率随...     

Spectroscopy, modeling, and laser operation of thulium-dopedcrystals at 2.3 μm

Pulsed room-temperature lasers based on the thulium 2.3-μm ³H₄-³H₅ transition have been achieved in 1.5% Tm:YAG, 2% Tm:LuAG, and 1.5% Tm:YLF crystals using a pulsed alexandrite laser at 785 nm as the pump source in a collinear geometry. The absorbed energy thresholds (slope efficiencies) for 1.5% Tm:YAG, 2% Tm:LuAG, and 1.5% Tm:YLF lasers are measured to be 1.2 mJ (14%), 1.8 mJ (13%), and 1.0 mJ (18%), respectively, which are in good agreement with the theoretically predicted results. The experimental results indicate 1.0 mJ thulium to be the most optimum concentration for 2.3-μm laser action. The thulium lasers are tuned around 2.3 μm using an intracavity single birefringent plate of quartz