Detailed investigation of thermal effects in longitudinally diode-pumped Nd:YVO/sub 4/ lasers

An investigation of thermal lensing effects in longitudinally diode-pumped Nd:YVO/sub 4/ lasers is made in detail both numerically and experimentally. A finite-element model is used to theoretically simulate thermal lensing in various Nd:YVO/sub 4/ crystals and pumping scenarios. The predicted values for thermally induced lens strengths are compared with experimentally observed results. We find that these two sets of results are in broad agreement, provided that the spatial profile of the pump-induced heat generation is accurately modeled. The saturation of the pump absorption is found to be of particular importance in producing an accurate prediction of the thermal lens strength, and a composite structure of the crystals is desirable to relieve the thermal lensing.     

Modeling of diode-pumped actively Q-switched lasers

The intracavity photon density and initial population inversion density in the diode-pumped actively Q-switched laser rate equations are assumed to be Gaussian distributions. These space-dependent rate equations are solved numerically and a group of general curves are generated. By using these curves and the related formulas, the pulse parameters of an arbitrary actively Q-switched laser can be easily estimated and an optimally coupled Q-switched laser can be designed. A sample calculation for a Q-switched Nd³⁺:YVO₄ laser is presented to demonstrate the use of the curves and the related formulas     

Tunable single- and double-frequency diode-pumped Nd:YAG lasers

An Nd:YAG 1-cm-long crystal has been used as the active medium for tunable single- and double-frequency lasers with a metallic absorbing thin-film selector. Cobalt and chromium thin films (210-nm thickness) were used for mode number and frequency control. The laser with a short cavity (25 mm) provided slow smooth tuning up to 6 GHz, the frequency chirp up to 4 GHz with repetition rate about 0.5 kHz and hop tuning over 150 GHz at a maximum pump power of 1.8 W. 520 mW of single-frequency output power was achieved. Double-frequency operation with a space of 1.5-2.5 GHz was realized in a laser with cavity length up to 100 mm     

Diamond cooling of high-power diode-pumped solid-state lasers

We have demonstrated the feasibility of cooling high-power solid-state lasers with diamond windows, whose thermal conductivity is about two orders of magnitude higher than that of sapphire. An output power of 200 W was achieved from a single Nd:YVO/sub 4/ slab in a zigzag configuration when pumped with 600-W diodes at 808 nm. The maximum output power previously reported in the literature using conventional cooling schemes is only about 100 W. A 2.3/spl times/4/spl times/24 mm/sup 3/ slab was pumped from its broad side (4/spl times/24 mm/sup 2/) through a 0.3-mm-thick optical diamond window placed in close contact with the lasing crystal. The diamond window, held in a water-cooled copper housing, acted as a heat conductor. The other broad side of the crystal was cooled directly by its water-cooled copper housing. Since pumping and cooling were along the same axis, a Cartesian thermal gradient was achieved, while the zigzag scheme was used to minimize thermal lensing. By using a BBO Q-switch, 70-W average power was obtained at 20 kHz with a pulse width of 19 ns and with a beam quality of 3 and 12 times the diffraction limit in the zigzag and transverse directions, respectively. The output of a two-head configuration was 295 W. In addition, a cavity was designed to achieve increased beam quality and 133 W was accomplished with a beam quality of 2 and 7.5 times diffraction-limited on the zigzag and nonzigzag axes, respectively. Operating this cavity with an RTP Q-switch produced 114 W with a beam quality of 1.5 and 9.5 on the respective two axes.     

Single-mode operation of diode-pumped Nd:YAG lasers by pump-beamfocusing

We present a theoretical study of the maximum single frequency power that can be obtained from a simple coaxially end-pumped Nd:YAG laser. The approach is general for four-level solid-state laser systems. It is shown that careful control of the pump beam geometry, cavity length, and crystal length can enhance single frequency performance     

Frequency noise measurement of diode-pumped Nd:YAG ring lasers

The combined frequency noise spectrum of two lightwave Model 120-01A nonplanar ring oscillator lasers was measured by first heterodyne detecting the IF signal and then measuring the IF frequency noise using an RF frequency discriminator. The results indicated the presence of a 1/f² noise component in the power spectral density of the frequency fluctuations between 1 Hz and 1 kHz. After incorporating this 1/f² into the analysis of the optical phase tracking loop, the measured phase error variance closely matches the theoretical predictions     

Efficient Nd:YAG slab longitudinally pumped by diode lasers

An efficient scalable 1.06-μm continuous-wave (CW) Nd:YAG slab laser longitudinally pumped by diode lasers is discussed. The 809-nm diode radiation is focused into every laser channel emerging from the reflection points of the 1.06-μm beam on the coated slab surfaces. A maximum CW TEM₀₀ output power of 675 mW has been obtained at a diode pump power of 2 W resulting in a slope efficiency of 40%     

Analysis of the line broadening of diode-pumped solid-state lasers

The output parameters of the most effective system for pumping of solid-state lasers that is based on laser diode arrays are studied. The spatial profile of radiation of specific diode arrays and the differences in the radiation spectra of emitting elements are determined. It is demonstrated that the main reason for the generation of additional modes and the spectral broadening of laser radiation is related to thermal effects resulting from the spatial nonuniformity of radiation of the diode pumping system.     

Power scaling of diode-pumped Nd:YVO/sub 4/ lasers

The evaluation of pump capability and scaling the output power of Nd:YVO/sub 4/ (vanadate) lasers are presented in this paper. Taking into account thermal fracture limitation and fundamental mode operation, systematic investigations of vanadate crystals have been conducted in an effort to scale the output power of diode-pumped lasers to higher levels. Based on the limitation of pump power, the input versus output power and beam propagation factor of vanadate lasers are optimized with knowledge of the thermal lensing effect and maximum pump power. The theoretical analyzes provide a good prediction for the output power of diode-pumped Nd:YVO/sub 4/ lasers, which is in agreement with the experiment. A practical example of a single-end-pumped vanadate laser is demonstrated with continuous-wave output powers of 9.8 W in the TEM/sub oo/ mode and 12.4 W in multimode.     

CW diode-pumped microlaser operation at 1.5-1.6 /spl mu/m in Er,Yb:YCOB

We report efficient laser operation at 1.5-1.6 /spl mu/m in an Er,Yb:YCOB laser. The maximum output power of 110 mW was achieved in a hemispherical cavity with a slope efficiency of 20%. We also report 100 mW of output in a flat-flat cavity configuration, and the first report of operation of this type of laser crystal in a true microchip arrangement with >10-mW output.     

Efficient wavelength conversion with high-power passivelyQ-switched diode-pumped neodymium lasers

Powerful CW diode-pumped Nd:YAG and Nd:YVO4 lasers Q-switched by Cr:YAG saturable absorbers demonstrate efficient (30%-60%) harmonic and parametric conversion, generating hundreds of milliwatts from ultraviolet to mid-infrared     

Scaling of KrF lasers for inertial confinement fusion

The scaling and design principles for a MJ-scale krypton fluoride laser are derived and applied. First, the scaling limits of size and operation of a single large-aperture module (oscillator or amplifier) are explained, and its performance evaluated. A new scheme for combining amplifier modules into high output power chains is then presented. The performance of this architecture is investigated, showing that it effectively produces both the total energy and pulselength required for inertial confinement fusion using existing technology, while maintaining an easily manageable level of system complexity and acceptable low flux levels on optical elements.     

Intensity noise in diode-pumped single-frequency Nd:YAG lasers andits control by electronic feedback

The power spectrum of the relative intensity noise (RIN) of single-frequency diode-pumped Nd:YAG lasers is observed to be shot-noise limited at frequencies above 20 MHz for a photocurrent of up to 4.4 mA. Relaxation oscillations result in noise 60-70 dB above shot noise at a few hundred kilohertz. These relaxation oscillations have been suppressed using electronic feedback     

Thermal lens and beam properties in multiple longitudinally diodelaser pumped Nd:YAG slab lasers

The focal length of the thermal lens and the beam quality factor (beam propagation factor) M² for a multiple longitudinally diode pumped slab laser is deduced for pump and output powers up to 16 and 4.5 W, respectively. Due to the geometry of the arrangement, a stronger thermal lens is observed in the plane with the larger pump spot radius as predicted by an analytical model for slab geometries. In addition, the second stable zone of an asymmetric resonator is found to be advantageous for improved beam properties at high output powers     

Satellite pulse generation in diode-pumped passively Q-switched Nd:GdVO/sub 4/ lasers

We have both experimentally and numerically investigated the satellite pulse generation in diode-pumped passively Q-switched Nd:GdVO/sub 4/ lasers with Cr/sup 4+/:YAG saturable absorber. We show experimentally that satellite pulse generation is a general effect of the lasers under strong pumping, and its formation is always associated with the appearance of strong Q-switched pulses. Satellite pulse generation of the lasers is further numerically simulated based on a coupled rate-equation model. Our numerical simulations show that the phenomenon is caused by the finite lifetime of the lower laser energy level of the lasers.     

Pulse energy scaling characteristics of longitudinally excited Sr+discharge recombination lasers

Pulse energy scaling of longitudinally excited Sr⁺discharge recombination lasers has been investigated for a series of tubes with active volumes of 30, 200, and 1000 cm³operating at low pulse repetition rates. Specific energy densities (sim 6-9 muJ/cm³in the short-pulse mode) and conversion efficiencies (∼ 0.1 percent) were found to remain approximately constant with increasing volume. Single pulse energies exceeding 6 mJ at λ 430.5 nm corresponding to peak powers aver 20 kW have been achieved.     

Influence of KTP length on the performance intracavity frequencydoubled diode-pumped Nd:YVO4 lasers

We demonstrate an experimental study of the influence of potassium titanyl phosphate (KTP) length on the performance of intracavity frequency-doubled diode-pumped Nd:YVO₄ lasers operating in continuous-wave (CW) mode and passive Q-switch mode. Theoretical and experimental results show that the optimum KTP length for CW mode is determined by the nonlinear coupling and walkoff effect and the highest optical conversion efficiency in CW mode is nearly 30% with a 10-mm KTP. On the other hand, a 2-mm KTP crystal, which is sufficient for efficient internal second-harmonic generation in a passive Q-switch mode, yield the highest peak green power of 240-W     

YCOB晶体非线性光学系数的标定及空间分布

通过实验确定了YCOB晶体的全部非线性系数 ,并用不同切向的YCOB晶体验证了由此决定的有效非线性系数的空间分布。结果表明 ,YCOB晶体的有效非线性系数在第二像限的θ =67° , =14 3 5°处具有最大值 ,为 1 73pm V。当长度为 5mm时 ,该切向晶体的倍频转换效率达到 4 1 5 %。     

Optimization of Er, Yb:YCOB for CW laser operation

The erbium and ytterbium ion concentrations in the host yttrium calcium oxaborate have been optimized for diode pumped continuous-wave (CW) laser operation using spectroscopic measurements, modeling of energy transfer and population rate equation analysis, resulting in 270 mW of CW output from a diode-pumped Er,Yb:YCOB laser.     

Efficient diode-pumped single-frequency erbium:ytterbium fiberlaser

We report a 7.6-mW single-frequency fiber laser operating at 1545 nm, using for the first time an Er³⁺:Yb³⁺ doped fiber and a fiber grating output coupler. The laser did not exhibit self-pulsation, which is a typical problem in short three-level fiber lasers, and had a relative intensity noise (RIN) level below -145.5 dB/Hz at frequencies above 10 MHz. The linewidth of the laser was limited by the relaxation oscillation sidebands in the optical spectrum and was typically less than 1 MHz