A supercontinuum white laser with ultrabroad bandwidth, intense pulse energy, and high spectral flatness can be accomplished via synergic action of third-order nonlinearity (3rd-NL) and second-order nonlinearity. In this work, we employ an intense Ti:sapphire femtosecond laser with a pulse duration of 50 fs and pulse energy up to 4 mJ to ignite the supercontinuum white laser. Remarkably, we use water instead of the usual solid materials as the 3rd-NL medium exhibiting both strong self-phase modulation and stimulated Raman scattering effect to create a supercontinuum laser with significantly broadened bandwidth and avoid laser damage and destruction. Then the supercontinuum laser is injected into a water-embedded chirped periodically poled lithium niobate crystal that enables broadband and high-efficiency second-harmonic generation. The output white laser has a 10 dB bandwidth encompassing 413 to 907 nm, more than one octave, and a pulse energy of 0.6 mJ. This methodology would open up an efficient route to creating a long-lived, high-stability, and inexpensive white laser with intense pulse energy, high spectral flatness, and ultrabroad bandwidth for application to various areas of basic science and high technology.
We report a 589-nm laser using the sum-frequency generation (SFG) of 1.158- and 1.197-μm Stokes Raman lasers. These Stokes lasers are based on two KGd(WO4)2 and Ba(NO3)2 external Raman laser oscillators. First, a high-energy 1064-nm source was built to pump stimulated Raman scattering. Multiorder Stokes lasers with pulse energies of 402 and 220 mJ were generated from Raman laser oscillators with 2.26-J pumping. Furthermore, these two Stokes beams were simultaneously delivered into a potassium dihydrogen phosphate crystal for SFG. Finally, a 31.7-mJ laser at 589 nm was achieved with pulse duration of 6.9 ns and repetition rate of 1 Hz. These experimental results provide practical alternative to generate high-energy short-pulse 589-nm laser beams for related applications.
We demonstrated a 50 mJ, 100 Hz, 355 nm UV laser. The third harmonic generated in a diode-pumped 200 mJ, 500 ps Nd:YAG laser system centered at 1064 nm, which based on a master oscillator power amplifier configuration. The pulse duration and temporal shape from oscillator could be modulated by an Arbitrary-Waveform-Generator and an amplitude modulator. Two LBO nonlinear crystals were employed to second and third harmonic generation respectively. The UV laser system featured an approximately flat-top temporal distribution and a 2.5% energy stability (RMS) within 1 hour.
We reported an active multipass stretcher which can deliver chirped pulse with high energy, adjustable duration and high beam quality. The stretcher system is based on a Martinez stretcher and a regenerative amplifier. The stretched pulse duration can be adjusted without changing the layout. With 1 ns stretched pulse output per roundtrip, chirped pulse with more than 10 ns can be obtained after several round-trips. A laser amplifier is introduced into the cavity to compensate the energy loss caused by the diffraction efficiency of gratings, and several millijoules pulse energy can be obtained after stretching and amplification. Benefit with the advantage of the regenerative structure, the stretched pulses have an excellent beam quality with M2 of 1.1. This novel stretcher is significant for high peak power laser systems.
To compensate for the gain saturation effect in the high-energy laser amplifier, a modified polarization beam combination (PBC) method is introduced to reshape temporal waveform of the injected laser pulse to obtain a controlled high-energy laser pulse shape after amplification. One linearly polarized beam is divided into two orthogonal polarized beams, which spatially recombine together collinearly after propagating different optical paths with relative time delay in PBC structure. The obtained beam with polarization direction being rotated by the following half wave plate is divided and combined again to reform a new beam in another modified polarization beam structure. The reformed beam is injected into three cascaded laser amplifiers. The amplified pulse shape can be controlled by the incident pulse shape and amplifier gain, which is agreeable to the simulation by the Frank–Nodvik equations. Based on the simple method, the various temporal waveform of output pulse with tunable 7 to 20 ns pulse duration can be obtained without interferometric fringes.
KEYWORDS: Laser damage threshold, Laser induced damage, Optical components, Near field optics, Thin films, Laser sources, Superluminescent sources, Near field, High power lasers, Modulation
An accurate evaluation method with an amplified spontaneous emission (ASE) as the irradiation source has been developed for testing thin-film damage threshold. The partial coherence of the ASE source results in a very smooth beam profile in the near-field and a uniform intensity distribution of the focal spot in the far-field. ASE is generated by an Nd: glass rod amplifier in SG-II high power laser facility, with pulse duration of 9 ns and spectral width (FWHM) of 1 nm. The damage threshold of the TiO2 high reflection film is 14.4J/cm2 using ASE as the irradiation source, about twice of 7.4 J/cm2 that tested by a laser source with the same pulse duration and central wavelength. The damage area induced by ASE is small with small-scale desquamation and a few pits, corresponding to the defect distribution of samples. Large area desquamation is observed in the area damaged by laser, as the main reason that the non-uniformity of the laser light. The ASE damage threshold leads to more accurate evaluations of the samples damage probability by reducing the influence of hot spots in the irradiation beam. Furthermore, the ASE source has a great potential in the detection of the defect distribution of the optical elements.
Pre-amplifier between the frontend and main power amplifier is the key unit of high power laser divers. The recent
progresses on the off-axis quadruple pass amplifier are presented, which include the beam path design, parasitic
oscillation research and experimental results. A single longitudinal mode, temporally shaped laser pulse with 5ns pulse
duration at 1053nm is injected into a Nd: Glass regenerative amplifier, which can provide a 12mJ energy output with
0.5% long term energy stability. The quadruple pass amplifier is designed as an off-axis pattern. With 1.3mJ energy
injection, amplified pulse with 16.5J can be achieved, and the measured output energy stability of the amplifier is 7.3%
(PV) at this output energy level, corresponding to a 21 shot result. The total gain of the amplifier is more than 10,000.
The parasitic oscillation was analyzed and discussed, and the parasitic mode and pencil beam are neither observed in the
experiment.
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