C.Y. Zhu

The Current Trends in SBS and phase conjugation

The current trends in stimulated Brillouin scattering and optical phase conjugation are overviewed. This report is formed by the selected papers presented in the “Fifth International Workshop on stimulated Brillouin scattering and phase conjugation 2010” in Japan. The nonlinear properties of phase conjugation based on stimulated Brillouin scattering and photo-refraction can compensate phase distortions in the high power laser systems, and they will also open up potentially novel laser technologies, e.g., phase stabilization, beam combination, pulse compression, ultrafast pulse shaping, and arbitrary waveform generation.

Numerical investigation of the effects of smoothing by spectral dispersion on stimulated rotational Raman scattering

The effect of smoothing by spectral dispersion (SSD) on stimulated rotational Raman scattering (SRRS) in air has been investigated both numerically and theoretically. The suppression effect of SSD on SRRS process is verified and it is demonstrated and proposed that the suppression effect is attributed to two aspects: the decreasing of the laser fluence modulation degree and the reducing of Stokes gain coefficient caused by the temporal and spatial variation of the phase of the incident laser pulse. The simulation results show that the SRRS threshold distance can be lengthened by choosing appropriate SSD parameters.

Mechanism of beam cleanup by stimulated Brillouin scattering in multimode fibers

The conditions leading to the beam cleanup effect induced by stimulated Brillouin scattering (SBS) have been debated by many researchers. In this paper, we firstly reveal that the key point of the beam cleanup induced by SBS is at the selective excitation of the fundamental mode of the Stokes beam, which is amplified by the counterpropagating high-order-mode pump beam along multimode fibers while preserving the fundamental mode and subsequently realizing the beam cleanup. This mechanism is theoretically modeled and experimentally demonstrated in this work.

High-precision small-scale laser focal spot measurements

In this paper, a method of two-dimensional fine-scanning with charge coupled device has been conducted to precisely measure spatial position and intensity distribution of small-scale focal spot (diameter in microns). The measurement accuracy of the small-scale focal spot position is better than 1 mu m when the fluctuations of the light energy and background noise are relatively small. The theoretical analysis is consistent with the experimental results.

Measurement of intrinsic Brillouin linewidth of fibers based on stimulated Brillouin scattering slow light

Intrinsic Brillouin linewidth is one of the essential parameters to optimize the gain spectrum of stimulated Brillouin scattering (SBS). A novel method for the measurement of the intrinsic Brillouin line-width based on SBS slow light is proposed and demonstrated. In this method, an implicit model based on the transient SBS theory is developed, and a data processing method is designed to obtain the value of the intrinsic Brillouin linewidth from the model. The measured results show that the method is effective for studying SBS slow light.

Investigation on the temporal characteristics of the pumps in high peak power pulse-pumped Yb-doped fiber amplifiers

This paper analyses the characteristics of the high peak power pulse laser amplification in a Yb-doped double-clad fiber amplifiers (YDFA-DC) pumped by pulse LD. The pump duration, the pump power and the delay time between the pump and the laser seed are discussed in detail, which are the most important parameters when such a fiber amplifier stage is designed.

Mode depression phenomena of SBS in large core (>100µm diameter) fibers

We experimentally investigate the Stimulated Brillouin Scattering (SBS) beam profile in very large core (105µm) fibers with nanosecond pulse. Both phase conjugation and mode depression effect in different conditions are achieved and studied. Beam shape of step-index (SI) fiber and graded-index (GI) fiber with same parameters are contrasted. And a mode clean up mechanism in GI fiber has been suggested.

Waveform transmission characteristics of high energy nanosecond pulse laser in 105µm diameter fiber

Waveform transmission characteristic of nanosecond pulse laser in both step-index(SI) fiber and grad-index (GI) fiber with very large diameter (105µm) fiber have been experimentally investigated. In SI fiber, different energy and fiber length are engaged in the experiments. Results show that the change of energy and fiber length will respectively produce different affect on pulse broadening and waveform aberration. In GI fiber, a pulse compression effect is also demonstrated with the shift of coupling location of incident light.

Acoustic waves dynamics and temporal characteristics of the phase conjugate waves in BEFWM

Acoustic field dynamics is one of the intrinsic determinations of the temporal characteristics of phase conjugate waves in Brillouin-enhanced four-wave mixing (BEFWM). Theoretical and experimental research illustrate that the fundamental origination of temporal modulations in the phase conjugate wave of BEFWM is perhaps the unsteady-state distribution and fluctuations of the acoustic wave.