Beam quality measurement of high power laser by using an involute pinhole array.

A novel method for power-in-the-bucket (PIB) measurement of high power laser beams is proposed. The laser beam spot was first sampled by a rotating involute pinhole array and then collected by using a photodetector placed behind the pinholes. The spatial-temporal distribution and calibrated PIB curve of the laser beam can be obtained. The spatial and temporal resolution is 20 µm and 5 ms, respectively. Compared with conventional methods, the proposed measurement method is simple, convenient, and accurate, which is suitable for high power laser beams with jitter.

Linearly excited indium fluorescence imaging for temporally resolved high-precision flame thermometry.

Two-line atomic fluorescence (TLAF) is a promising technique for two-dimensional (2D) flame thermometry. However, it suffers either from a low signal-to-noise ratio (SNR) when excited in the linear regime or a quenching effect and nonlinear behavior in the nonlinear regime. This work aims to develop a new TLAF modality, which can overcome the aforementioned limitations based on a specifically designed laser source that can generate long pulses (∼400ns) with a moderate energy of ∼0.9µJ and operate at a repetition rate up to ∼22kHz. A proof-of-concept experiment was conducted and linearly excited fluorescence images with an SNR up to ∼14 were obtained within 1 ms acquisition time by synchronizing the laser with the microchannel plate (MCP) of a 10 Hz-rate intensified camera. The SNR achieved was comparable to that of a traditional nonlinear TLAF implementation and superior to a conventional linear TLAF approach. This approach offers a novel solution for recording linearly excited indium fluorescence images and is expected to make TLAF a temporally resolved and high-precision 2D thermometry for the first time.

Thermal modeling of high-power Yb-doped fiber lasers with irradiated active fibers.

With both radiation effects and thermal effects taken into consideration, a multiphysics thermal model concerning high-power Yb-doped fiber lasers operated with post-irradiated active fibers is established. Radiation-related parameters, including propagation losses, refractive indexes and lifetime, are considered. And, with the temperature profile of the active fiber, temperature-dependent parameters, including absorption and emission cross-sections, refractive indexes and lifetime, are updated every loop to simulate the output parameters. Simulation results show that radiation induces great changes to the thermal profiles of the active fiber. And severe performance degradation of high-power Yb-doped fiber lasers are recorded, featuring a remarkable drop in output power and an even steeper decline in the transverse mode instability threshold, which is a predominant limitation at high radiation doses. With a deposited radiation of 100 Gy, an output decline of about 50% and a mode instability threshold drop over 85% are observed. And it's shown that, with the exploited active fiber, it's hardly possible for the investigated fiber laser to generate stable single-mode output at kilowatt levels with accumulated radiation doses beyond 50 Gy. At low radiation doses within 20 Gy, to maintain safe and stable single-mode operation of the laser system, longer active fibers with lower absorption coefficients are preferred despite a small rollover of the output power.

High energy closed-loop cycle narrow linewidth optically pumped XeF(C-A) blue laser at a repetition rate of 10 Hz.

We report for the first time on a closed-loop cycle narrow linewidth XeF(C-A) blue laser at a repetition rate of up to 10 Hz with each pulse energy of >1 J. A FWHM linewidth of less than 1.5 nm (minimum to 1.1 nm) with a highly stable wavelength centered at 488.3 nm was achieved by employing a polarization-independent custom-designed narrowband optical filter (NBOF) into the cavity. The pulse energy, as well as the repetition rate, to the best of our knowledge, is the highest ever reported in the narrow linewidth XeF(C-A) blue lasers at repetitively-pulsed mode.

Wavelength-tunable passively mode-locked mid-infrared Er3+-doped ZBLAN fiber laser.

A passively mode-locked Er3+-doped ZBLAN fiber laser around 3 µm with a wide wavelength tuning range is proposed and demonstrated. The laser cavity was comprised of a semiconductor saturable absorber mirror and a blazed grating to provide a wavelength tunable feedback. The central wavelength of the mode-locked fiber laser can be continuously tuned from 2710 to 2820 nm. The pulse train had a maximum average power of higher than 203 mW, a repetition rate of 28.9 MHz and a pulse duration of 6.4 ps, yielding a peak power of exceeding 1.1 kW. To the best of our knowledge, this is the first demonstration of a wavelength-tunable passively mode-locked mid-infrared fiber laser at 3 µm.

Watt-level passively Q-switched heavily Er(3+)-doped ZBLAN fiber laser with a semiconductor saturable absorber mirror.

A diode-cladding pumped mid-infrared passively Q-switched Er(3+)-doped ZBLAN fiber laser with an average output power of watt-level based on a semiconductor saturable absorber mirror (SESAM) is demonstrated. Stable pulse train was produced at a slope efficiency of 17.8% with respect to launched pump power. The maximum average power of 1.01 W at a repetition rate of 146.3 kHz was achieved with a corresponding pulse energy of 6.9 µJ, from which the maximum peak power was calculated to be 21.9 W. To the best of our knowledge, the average power and the peak power are the highest in 3 µm region passively Q-switched fiber lasers. The influence of gain fiber length on the operation regime of the fiber laser has been investigated in detail.