Weiming He

High amplification and low noise achieved by a double-stage non-collinear Brillouin amplifier

We report a double-stage non-collinear Brillouin amplifier structure with high amplification and low noise, achieving an energy amplification of 6 x 10(11) and a signal-to-noise ratio of 10(3) for an input signal of 5.5 x 10(-14)J in the regime above the pumps stimulated Brillouin scattering threshold. The signal of the first-stage amplifier is efficiently amplified and separated from the noise output. The saturation amplification with noise suppressing is implemented in the second stage. The design principles of system parameters such as the intersection angle between the pump and signal beams, the pump energy, and the beam diameter are given.

Phase matching for noncollinear Brillouin amplification based on controlling of frequency shift of Stokes seed

A method to compensate phase detuning, which will lead to the low efficiency in noncollinear Brillouin amplification by controlling the frequency shift of Stokes seed, is proposed. The efficiency of noncollinear Brillouin amplification can be sustained at the level of collinear Brillouin amplification for a large crossing angle. For crossing angles between Stokes and pump of 20° and 35°, the Brillouin gain coefficient is improved 1.24 and 4.93 times, accordingly.

Using an active temporal compensating system to achieve the super-Gaussian pulses in high-power lasers

In high-power solid-state laser, initiative pulse shaping can help improve the output laser’s performance. The evaluation for output laser pulse is also incomplete. In this paper, we propose a method of initiative pulse shaping by using arbitrary waveform generator (AWG), and establish a relatively complete evaluation system for the output pulses shape simultaneously. It achieves the super-Gaussian pulse output with high SNR (signal-to-noise ratio). As a consequence, a square laser pulse with pulse adjustable width ~5ns, rising time 197ps is obtained. The power imbalance of the output square pulse is 3.72%. The similarity between the eight-order super-Gaussian pulse and the one we get from experiment reached 99%.

Orbital angular momentum mode division filtering for photon-phonon coupling

Stimulated Brillouin scattering (SBS), a fundamental nonlinear interaction between light and acoustic waves occurring in any transparency material, has been broadly studied for several decades and gained rapid progress in integrated photonics recently. However, the SBS noise arising from the unwanted coupling between photons and spontaneous non-coherent phonons in media is inevitable. Here, we propose and experimentally demonstrate this obstacle can be overcome via a method called orbital angular momentum mode division filtering. Owing to the introduction of a new distinguishable degree-of-freedom, even extremely weak signals can be discriminated and separated from a strong noise produced in SBS processes. The mechanism demonstrated in this proof-of-principle work provides a practical way for quasi-noise-free photonic-phononic operation, which is still valid in waveguides supporting multi-orthogonal spatial modes, permits more flexibility and robustness for future SBS devices.

Pulse temporal compression by two-stage stimulated Brillouin scattering and laser-induced breakdown

A laser pulse temporal compression technique combining stimulated Brillouin scattering (SBS) and laser-induced breakdown (LIB) is proposed in which the leading edge of the laser pulse is compressed using SBS, and the low intensity trailing edge of the laser pulse is truncated by LIB. The feasibility of the proposed scheme is demonstrated by experiments in which a pulse duration of 8u2009ns is compressed to 170 ps. Higher compression ratios and higher efficiency are expected under optimal experimental conditions.

A promotion of stability for temporal compression based on SBS in an interferometric scheme

Abstract An approach that introducing a standing wave into focal area to stabilize the output energy and duration of stimulated Brillouin scattering (SBS) compression is presented. An interferometric scheme filled with FC-770 is used to improve the stability of both output energy and duration two times compared with an equivalent conventional SBS compressor. Moreover, the interferometric scheme shows a promotion for the performance of SBS compression.

Experimental and numerical investigation of amplification of strongly nonstationary stimulated Brillouin scattering

It is investigated that the duration of stimulated Brillouin scattering (SBS) amplification of Stokes pulses is smaller than the acoustics lifetime and the oscillation period of hypersound with the nanosecond pulse as pump light. In the experiment, the Fluorinert (FC-72) is used as the Brillouin amplification medium, the Stokes pulse duration less than 1/4 of oscillation period of hypersound of FC-72 as seed pulse is achieved by two-stage SBS compressor to compress 8ns laser pulse. The experiment and simulation show that, in this case, their energy amplification is efficient, but the duration of amplified pulses is longer than the initial seed pulse. Simulation results of higher energy than the maximum energy in the experiment show that at sufficient high pump or initial seed pulse power intensity, the duration of amplified pulses can be no larger than the initial seed pulse duration., even less than the seed pulse duration.

Generation of Controllable High Energy Nanosecond Flat-Top Waveform Based on Brillouin Amplification

We propose a method based on Brillouin amplification, which reshapes the Gaussian pulse generated from a Q -switched laser into the flat-top waveform. The numerical simulations show that the reshaped waveform depends on Stokes pulse width and energy, and optimum conditions for a flat waveform are also investigated. It is demonstrated experimentally by the independent two-cell filled with FC-40 liquid. In the experiment, the flat-top waveform pulses with width from 9.1 to 13.3 ns and continuously adjustable energy from 90 to 210 mJ are obtained at the wavelength of 1064 nm. The pulses with flat-top waveform and high energy are achieved by injecting a small Stokes seed into the Brillouin amplifier, which is a novel method to obtain high-energy flat-top laser pulses.

Brillouin amplification of weak stokes signals from water based on a double-stage non-collinear system with mixture medium

A scheme is presented for amplifying weak Stokes signals from water using mixture medium of CS<inf>2</inf>/CCl<inf>4</inf> in a double-stage non-collinear Brillouin amplification system. A frequency doubled Nd:YAG laser is used to produce single-mode pulses of 5.5-ns duration. Results show that choosing mixture liquid of CS<inf>2</inf>/CCl<inf>4</inf> as amplifier medium has advantages over pure CS<inf>2</inf>. Maximum gain can be obtained by changing the mixed ratio of medium to eliminate the difference of the Brillouin frequency shift between the generator and amplifier. Signal gain as high as 10¹¹ is experimentally achieved with an input signal of 8.6×10⁻¹⁴J using the mixture of 90% CS<inf>2</inf> and 10% CCl<inf>4</inf> as the amplifier medium.

The performance of stimulated Brillouin scattering pulse improved by a prepulse seed

SBS with a prepulse injection has been investigated through experiment. We have measured the threshold, waveform fidelity, energy reflectivity, stability and discussed the factors which lead to the changes of output pulse shape, and also the principles are achieved. Results show that a suitable delayed time between the prepulse and the main-pulse can shorten the leading edge and enhance the fidelity. A suitable energy ratio of the prepulse to the main-pulse can improve the reflectivity stability. The result indicates that the experimental program can improve the waveform of the Stokes pulse and the stability of the reflectivity. Theoretical calculation formula is used to simulate these results numerically. The threshold and energy reflectivity are also studied. And the theoretical results are consistent with that of experiment.