Amplified Laser Beam Research Articles

Multistage Diode-Pumped Nd:YAG Optical Amplifier with Correction of Amplified Laser Beam by Thermally Induced Lenses of Active Elements

Multistage Diode-Pumped Nd:YAG Optical Amplifier with Correction of Amplified Laser Beam by Thermally Induced Lenses of Active Elements

Characterization of the Carrier Lensing Effect in a Second Harmonic Generator

This paper presents studies on the carrier lensing effect of a tapered amplifier in a compact cavity-enhanced second harmonic generator. When different injecting currents are applied, carriers in the tapered amplifier are depleted to different levels depending on the local optical field intensity, resulting in a spatial variation of the refractive index and creating an effective convex lens for the amplified laser beam. This can significantly reduce the mode matching between the pump beam and the cavity, leading to a degradation of the second harmonic generator efficiency. To characterize this effect and provide guidance for mode matching, the evolution of optical fields and carriers in the tapered amplifier is simulated numerically with Maxwell-Bloch equations. The effective focal length of the tapered amplifier is calculated theoretically and verified with experimental calibration. Based on these results, the coupling optics of the cavity can be properly designed so as to achieve a high coupling efficiency. Finally, a single-frequency continuous-wave laser at 461 nm is achieved, with an output power exceeding 500 mW and a conversion efficiency of 33%.

Ultrafast thin-disk multipass laser amplifier scheme avoiding misalignment induced by natural convection of the ambient air

We report on an approach for a compact ultrafast thin-disk multipass laser amplifier making use of a highly compact geometric folding scheme. The setup is also suitable to minimize the effects caused by natural convection of hot air in front of the thin-disk on the amplified laser beam as it facilitates to orient the laser disk with its axis in the vertical direction. The efficacy of this approach is analyzed with finite-element method simulations of the heated laser crystal in ambient air with different orientations of the thin laser disk. The experiments confirm a significant improvement of the amplifier performance in terms of stability and an increase of the output power with nearly diffraction-limited beam quality (<italic>M</italic>² ≤ 1.4) by a factor of 3 with respect to the conventional orientation of the laser disk.

Multi-watt amplification in a birefringent Yb:LiLuF4 single crystal fiber grown by micro-pulling-down

We present, to the best of our knowledge, the first demonstration of a single crystal fiber solid-state amplifier based on a birefringent Yb3+-doped thin crystal grown by the micro-pulling-down method. We measured a small signal gain >30 in a four-passes Yb:LiLuF4 amplifier pumping with a 120-W maximum power fiber-coupled laser diode. At an absorbed pump power of 80W, a maximum output power of 8.4W was obtained seeding the 42-mm-long, 2%Yb3+-doped single crystal fiber sample with 0.8W at 1021nm. Even at the maximum incident pump power, the amplified laser beam polarization and spatial quality were excellent (M2=1.15×1.06).

Wavefront evolution of the signal beam in Ti:sapphire chirped pulse amplifier**Project supported by the National Natural Science Foundation of China (Grant No. 61775223) and the Strategic Priority Research Program of Chinese Academy of Sciences (Grant No. XDB1603).

We studied the evolution of wavefront aberration (WFA) of a signal beam during amplification in a Ti:sapphire chirped pulse amplification (CPA) system. The results verified that the WFA of the amplified laser beam has little relation with the change of the pump beam energies. Transverse parasitic lasing that might occur in CPA hardly affects the wavefront of the signal beam. Thermal effects were also considered in this study, and the results show that the thermal effect cumulated in multiple amplification processes also has no obvious influence on the wavefront of the signal beam for a single-shot frequency. The results presented in this paper confirmed experimentally that the amplification in a Ti:sapphire CPA system has little impact on the WFA of the signal beam and it is very helpful for wavefront correction of single-shot PW and multi-PW laser systems based on Ti:sapphire.

Amplification of flat laser pulse train.

We present modeling and measurements of flattop amplification of a laser pulse train in a diode pumped Nd:YLF system. We establish a theoretical model, accounting for the transverse Gaussian shape of an amplified laser beam, in order to explain remaining slopes in the pulse train energy. The influence of the transverse Gaussian shape on the train's flatness has been experimentally verified. Based on the model we are able to increase the total amplification of a long train of infrared seed beam in the drive laser system at the Fermilab Accelerator Science and Technology facility. The single-pass amplifier improvements resulted in a gain of ∼7 with flat output pulse train for up to 1000 seed pulses.

Amplification of Conically Diverging Laser Beams in the Gas Amplifier of the THL-100 Laser System

Amplification of conically diverging laser beams in the XeF(C-A) amplifier of the THL-100 hybrid laser system operating in the visible range (λ = 475 nm) is investigated experimentally and theoretically. Energies of 2 and 2.5 J are obtained experimentally and theoretically at the output from the XeF(C-A) amplifier for the chirped start pulse with energy of 0.8 mJ and duration of 2 ps. Patterns of changes of energy and spatial and temporal distribution of the amplified laser beam intensity are investigated theoretically. The maximal calculated energy density and the radiation pulse intensity are Wmax = 100 mJ/cm2 and Imax = 64 GW/cm2, respectively.

A multipass Ti:sapphire laser amplifier pumped with homogenized Nd:YAG lasers

A speckle pattern is observed when a neodymium-doped yttrium aluminum garnet (Nd:YAG) laser is homogenized by a diffractive optical element (DOE) due to its high spatial coherence. Therefore, a Nd:YAG laser homogenized by a DOE was previously considered not suitable to pump a Ti:sapphire laser amplifier. However, we show by experiment and simulation that the speckle structure does not manifest itself in the final amplified Ti:sapphire laser beam. By using the homogenizer, a smooth distribution of the amplified laser beam is obtained. No degradation of the energy, the wavefront, and the temporal characteristics of the amplified laser beam is observed.

270-W 15-kHz MOPA System Based on Side-pumped Rod-type Nd:YAG Gain Modules

We have developed a 270-W 15-kHz MOPA system based on side-pumped rod-type Nd:YAG gain modules. The master oscillator is a 3-W 15-kHz <TEX>$TEM_{00}$</TEX> <TEX>$Nd:YVO_4$</TEX> laser with a pulse duration of 30 ns. To preserve the high beam quality during the amplification, we use image relay and polarization rotation which can simultaneously compensate for thermal lensing and thermal birefringence generated in the rod-type gain modules. After the amplification to 270 W with six rod-type gain modules, the beam quality factor (<TEX>$M^2$</TEX>) of the amplified laser beam is 5-10, and the pulse duration is maintained at 30 ns.

Detection of a two-photon transition by stimulated emission: Amplification and circular birefringence

We present the detection of a two-photon transition based on stimulated emission. This measurement was performed in rubidium for the 5S-5D{sub 5{approx}}{sub sol{approx}}{sub 2}-5P{sub 3{approx}}{sub sol{approx}}{sub 2} transition, using two low-cost diode lasers. Several detection schemes were tested. We reached the best results by probing the circular birefringence of the excited vapor, with the polarization analysis of the amplified laser beam.

Compact soft x-ray source using Thomson scattering

A compact soft x-ray source using Thomson scattering, enabled by the combination of a picosecond laser and an electron rf gun, was developed aiming at biological studies such as those using an x-ray microscope. The x-ray source included both a photoinjector system and a picosecond laser system with a tabletop size of 2×2m2. An infrared laser beam (λ0=1047nm) was obtained from an all-solid-state mode-locked Nd:YLF laser system and injected into the photocathode of an accelerator system. A 4.2MeV electron beam was generated from a laser-driven photocathode rf gun system. The residual laser beam was amplified up to about 4.2mJ/pulse using a flash-lamp-pumped laser amplifier. Upon collision of the electron beam with the amplified laser beam, 300eV soft x rays were generated by Thomson backscattering. The stable interaction between the two beams was achieved using the same seed laser pulse for irradiating the photocathode and the scattering process with laser photons.

Study of a compact three-electrode oscillator-amplifier excimer laser system

We present the design and performance details of IANUS, a three-electrode XeCl excimer laser operated as a power-oscillator power-amplifier system. The oscillator, equipped with a generalised self-filtering unstable resonator, delivers a very low divergence laser beam, which is only 1.1 times its own diffraction limit and 1.3 times the diffraction limit of the equivalent gaussian beam. In spite of its long pulsewidth (85 ns FWHM), the single-pass amplified beam reaches a high radiance value of B = 3 × 10 14 W cm −2 ster −1. Both the oscillator and the amplified laser beam have excellent pointing stability. The limiting factors and the possible improvements of the IANUS performance are discussed.

Radiation self-interaction effects in a cw CO2amplifier

Three-dimensional numerical calculations made of the radiation parameters of a cw CO2 amplifier with a circulating active medium. An analysis was carried out of the amplification of Gaussian and annular-profile beams. The calculated energy characteristics of the output radiation showed a satisfactory agreement with the experimental data. The angular divergence of the output beam was 1.5–2 times greater than the diffraction limit because of local temperature inhomogeneities. As a result of self-interaction of the radiation, splitting of the amplified laser beam was possible in the far-field zone. Under selected conditions the upstream angular shift of the output beam did not exceed its divergence.