YAG Slab Laser Research Articles

A modified model for the LD pumped 2 μm Tm:YAG laser: Thermal behavior and laser performance

A modified three-dimensional (3-D) plane-wave model is developed to analyze the laser performance and temperature distribution in an end-pumped Tm:YAG slab laser. A numerical iterative method is used to calculate the stable distributions of laser intensity and temperature. This three-dimensional model provides a more practical method than traditional 2-D model to analyze laser systems with non-uniform temperature distribution. Experiments using Tm:YAG ceramic slabs are carried out to examine the influence of coolant fluid temperature on laser output. The experimentally acquired data are found to be in reasonable agreement with the theoretical predictions.

4350W quasi-continuous-wave operation of a diode face-pumped ceramic Nd:YAG slab laser

Abstract A high efficiency and high power laser diode (LD) face-pumped quasi-continuous-wave (QCW) ceramic Nd:YAG zigzag slab laser is demonstrated. The shape of the LD pump beam is optimized to ensure that the pump size is well matched with the ceramic slab and to improve the uniformity of the intensity distribution along the length and width direction of the ceramic slab. Meanwhile, an efficient cooling technique is adopted to obtain the uniform temperature distribution inside the ceramic slab. Under the LD pump power of 9.98 kW, a maximum average output power of 4.35 kW at 1064 nm is demonstrated at a pulse repetition frequency of 400 Hz, corresponding to an optical to optical conversion efficiency of 43.6%. To the best of our knowledge, this is the highest output power as well as the highest conversion efficiency reported for face-pumped QCW ceramic Nd:YAG single slab laser.

Compact and high-energy diode-side-pumped Q-switched Nd:YAG slab laser system for space application

We develop a compact and high-energy Nd:YAG slab laser system consisting of an oscillator and an amplifier for space applications. The oscillator is a diode-side-pumped electro-optically Q-switched slab laser with a cross-Porro resonator. The KD*P Pockels cell with a low driving voltage of 950 V is used to polarization output coupling. The amplifier is a Nd:YAG zigzag slab pumped at bounces. The maximum output pulse energy of 341 mJ with 13 ns pulse duration is obtained from the system at the repetition rate of 20 Hz and the beam quality factors are M 2 x = 3.1 and M 2 y = 3.5. The beam pointing stabilities of the laser system are 3.05 ?rad in the X-direction and 3.99 ?rad in the Y-direction, respectively.

Cryogenic, high power, near diffraction limited, Yb:YAG slab laser

A cryogenic slab laser that is suitable for scaling to high power, while taking full advantage of the improved thermo-optical and thermo-mechanical properties of Yb:YAG at cryogenic temperatures is described. The laser uses a conduction cooled, end pumped, zigzag slab geometry resulting in a near diffraction limited, robust, power scalable design. The design and the initial characterization of the laser up to 200W are presented.

百瓦级高光束质量Nd:YAG板条激光放大器

百瓦级高光束质量Nd:YAG板条激光放大器

Laser-plasma extreme ultraviolet source at 6.7 nm using a rotating cryogenic Xe target

A laser-plasma source comprising a rotating cryogenic solid-state Xe target has been studied for use in extreme ultraviolet lithography (EUVL) systems equipped with La/B4C mirrors. The laser-to-EUV power conversion efficiency (CE) of the cryogenic Xe target was improved to achieve a maximum CE of 0.15 % at 6.7 nm with 0.6 % bandwidth. We successfully demonstrated the continuous generation of EUV light with an average power of 80 mW at 6.7 nm with 0.6 % bandwidth using a Nd:YAG slab laser at a repetition rate of 320 Hz and an average power of 100 W. Scaling-up of the laser-plasma source for use as a future EUVL source is also discussed.

250 mJ, self-adaptive, diode-side-pumped Nd:YAG slab laser

A scheme of self-adaptive, closed-loop, diode-side-pumped Nd:YAG slab laser was presented. As a result of four-wave mixing of standing waves intersecting at a small angle in a closed-loop cavity, the self-adaptive process of beam cleaning leading to fundamental mode operation despite severe asymmetry of the inversion profile and thermal-optical distortion was achieved. The output beam was extracted from the cavity as the first- order diffraction beam on the dynamic gain gratings created in an active medium. The near-diffraction-limited (parameter M(2)<1.4, divergence of 1 mrad) output beam of 250 mJ energy and the optical slope efficiency of 30% at a repetition rate of up to 25 Hz in a free-running regime were demonstrated.

Unexpected temperature rise in end-pumped Nd3+:YAG composite slab laser

Unexpected temperature rise is observed in end-pumped YAG–Nd3+:YAG–YAG slab laser experimentally. The measured optical absorption spectrum of undoped YAG in 780–830nm indicates an absorption coefficient of 0.015cm−1 at 808nm. The influence of the weak absorption on temperature distribution in end-pumped composite slabs is analyzed numerically and a good agreement with infrared measurement is achieved. The results of finite element analysis show that longer heat sinks and wider slabs bring lower temperature.

High efficiency diode-pumped slab oscillator and amplifier for space-based application

The design and performance of conduction-cooled, laser diode-pumped oscillator and amplifier slab laser featuring high efficiency, high pulse energy and high beam quality for space-based application are reported. The oscillator was a diode-pumped Q-Switched Nd:YAG slab laser using unstable resonator, and the amplifiers were two zig-zag Nd:YAG slabs based on a side-pumped slab geometry. A near diffraction-limited output of 450 mJ in a 10 ns pulse at a repetition rate of 20 Hz was obtained, corresponding to an optical-to-optical conversion efficiency of over 20%.

Characterization of a laser-plasma extreme-ultraviolet source using a rotating cryogenic Xe target

A laser-plasma source for extreme-ultraviolet (EUV) light that uses a rotating cryogenic solid-state Xe target has been characterized. We focused on parameters at the wavelength of 13.5 nm with 2% bandwidth required for an EUV lithography source and investigated improvements of the conversion efficiency (CE). With the drum rotating, there was an increase in CE and less fast ions compared with the case for the drum at rest. It is considered that the Xe gas on the target surface can produce optimal-scale plasma, and satellite emission lines in Xe plasma effectively increase the EUV intensity, and the ion number is decreased by the gas curtain effect. The dependence of CE on the laser wavelength, laser energy and intensity also studied. As a result, the maximum CE was 0.9% at 13.5 nm with 2% bandwidth under the optimal condition. By continuous irradiation of a Nd:YAG slab laser at a repetition rate of 320 Hz and an average power of 110 W, the target continuously generated EUV light with an average power of 1 W at 13.5 nm with 2% bandwidth. The achieved performances provide valuable information for the design of a future EUV lithography source.

千瓦级二极管激光侧面抽运Nd:YAG板条激光器

千瓦级二极管激光侧面抽运Nd:YAG板条激光器

Diode end-pumped high-power Q-switched double Nd:YAG slab laser and its efficient near-field second-harmonic generation

We reported on an all-solid-state double Nd:YAG slab laser. The laser was based on two diode end-pumped Nd:YAG slabs and a stable-unstable hybrid resonator. A cw output of 189 W and an average Q-switched output of 169 W at 10 kHz with an M(2) factor of 1.5 in the slow direction and 1.7 in the fast direction were obtained. We demonstrated efficient near-field frequency doubling by imaging the one-dimensional top-hat near-field to a lithium triborate frequency doubler. We obtained 93 W green light at 10 kHz with a pulse width of 10.7 ns. The efficiency of second-harmonic generation was up to 57%.

边缘泵浦被动调Q的Nd：YAG薄片激光器

We report a high-power thin Nd:YAG slab laser with slab dimension of 1 mm × 10 mm × 60 mm partially edge-pumped by diode laser arrays. Passive Q-switching is achieved with a Cr4+YAG microchip adopted as the saturable absorber mirror. The pulse duration is around 10 ns while the pulse repetition rate is higher than 10 kHz. The average output power of 70 W is obtained with a slope efficiency of 36%. The diffraction limited beam quality in the thickness direction is obtained by controlling the pump beam diameter inside the slab. The laser head is very compact with size of only 60 × 70 × 150(mm).

EUV Light Sources by Laser-Produced Plasmas Using Cryogenic Xe and Li Targets

As for deposition-free-targets, cryogenic Xe and Li targets of laser- produced-plasma have been studied for extreme ultraviolet (EUV) light sources. A fast rotating cryogenic drum system, which can continuously supply a solid Xe target, has been developed. It successfully generated about 1 W of EUV power by continuous irradiation of Nd: YAG slab laser at 320 pps, with a maximum conversion efficiency of 0.9%. Experimental results for the Xe target of the double-pulse and short-wavelength irradiation have also been reported. In addition, a new Li target using a forced-recombination scheme was demonstrated. It was found that the maximum conversion efficiency was 2.3% with a laser irradiation of 532nm in Li planar targets. By using both direct EUV emissions and forced-recombination emissions, higher efficiency can be achieved.

High efficiency TEM 00 mode, diode-pumped, conduction-cooled, Nd:YAG zig-zag slab laser

We report a compact, conduction-cooled, highly efficient, continuous wave (CW) Nd:YAG slab laser in diode-side-pumped geometry. To achieve high efficiency, a novel laser head for Nd:YAG slab has been developed. For an absorbed pump power of 27.6 W, maximum output power of 10.4 W in multimode and 8.2 W in near-diffraction-limited beam quality has been obtained. Slope and optical-to-optical conversion efficiencies are 45.3% and 37.7% in multimode with beam quality factors ( M 2) in x and y directions equal to 32 and 8, respectively. TEM 00 mode operation was achieved in a hybrid resonator with slope and optical-to-optical conversion efficiencies of 43.2% and 29.7%, respectively. Beam quality factors in x and y directions are ⩽1.5 and ⩽1.6 for the whole output power range. The laser radiation was linearly polarized and polarization contrast ratios are >1200:1 in the multimode and 1800:1 in the TEM 00 mode operation. In passive Q-switching with Cr 4+:YAG crystal of 68% initial transmission, 18 ns pulsewidth has been achieved with an average power of 2 W at a repetition rate of 16 kHz.

A Compact 532-nm Source by Frequency Doubling of a Diode StackEnd-Pumped Nd:YAG Slab Laser

A near-diffraction-limited green source is generated at 1 kHzrepetition rate by frequency doubling of a diode stack end-pumpedelectro-optically Q-switched Nd:YAG slab laser. We obtain 9.7 mJ greenlight with pulse width of 12.2 ns at a repetition rates of 1 kHz. Thepump to green optical conversion efficiency is 12.9%. The energy pulsestability at 532 nm is about 0.8%.

Effects of the temperature dependence of absorption coefficients in edge-pumped Yb:YAG slab lasers

A study of the temperature dependence on an absorption coefficient is presented. We describe the absorption spectrum measurement of the laser material Yb:YAG that was performed over a wide temperature range. As the temperature increases from 23°C to 300°C, the central wavelength of the Yb:YAG absorption spectrum at 940 nm varies slightly from 941.2 nmto941.1 nm, and the maximal absorption cross section drops dramatically from 7.89×10−21 cm2 to 4.23×10−21 cm2. According to our experimental results, we have presented an analytic description of temperature distribution with the numerical iterative method and have investigated the pumping optimization and laser oscillator performance, taking into account that the absorption coefficient is strongly influenced by temperature. Our analyses also include the effect of pump absorption saturation and the temperature dependence of Boltzmann population fractions, stimulated emission cross section, and thermal conductivity. We have shown that the predicted laser output power exceeds the actual value if the temperature dependence of Yb:YAG's absorption coefficient is neglected.

Thin Nd:YAG slab laser pumped by lens duct coupled diode laser stacks

High power continuous wave operation of a diode face-pumped thin Nd:YAG slab laser is reported. A novel pumping geometry for a thin Nd:YAG slab using cylindrical lens duct coupled diode laser stacks is demonstrated. In a close-coupled resonator, a maximum laser output power of 260 W in multimode operation is obtained. This corresponds to a slope efficiency of 34% and an optical-to-optical efficiency of 27%, respectively. In high-brightness operation, a polarized laser output of 70 W has been obtained with a beam quality factor close to 4 in both directions. The polarization contrast ratio is >100.

Propagation parameters of the beam extracted from a diode pumped Nd:YAG ceramic slab laser with a hybrid stable–unstable resonator

We analyze the propagation properties of the beam extracted from a diode pumped ceramic Nd:YAG slab laser adopting a hybrid stable–unstable resonator. Such a resonator produces a beam characterized by an Hermite–Gauss mixture-like distribution in one transverse direction and a hard-edge diffracted distribution on the other transverse direction. The beam propagation parameters M x 2 and M y 2 are measured for different values of the diodes driving current. We obtain a beam parameter product smaller than 3 mm mrad in both transverse directions and in the whole range of powers, up to an extraction of 220 W in a QCW regime.

Design and characterization of a diode-pumped Nd:YAG retroreflecting slab laser

We describe the design and lasing characteristics of a miniaturized, chip-scale Nd:YAG slab laser. The Nd:YAG laser slab utilizes a retroreflecting corner to achieve a 17-cm optical path length with slab geometry of 10×12×2 mm. The laser is constructed, tested, and shown to successfully lase at 1064 nm under edge pumping with an AlGaAs diode laser at 808 nm. The slab laser is operated in a pulsed-pump excitation mode and shown to support a TEM10 single output mode. The fluence achievable from the edge pumping of this initial cavity geometry results in a 6.0% experimentally measured lasing efficiency.