Stimulated Brillouin Scattering Signal Research Articles

Calibration of the sub-aperture backscatter system on OMEGA EP

The sub-aperture backscatter (SABS) diagnostic on the OMEGA EP Laser System [Waxer etal., Opt. Photonics News 16, 30 (2005)] is a diagnostic that is used to measure the backscattered and sidescattered light during laser-plasma interaction experiments [W. L. Kruer, The Physics of Laser Plasma Interactions, Frontiers in Physics Vol. 73, edited by D. Pines (Addison-Wesley, Redwood City, CA, 1988) and Myatt etal., Phys. Plasmas 21, 055501 (2014)] that are relevant to high-energy-density physics and inertial confinement fusion. The diagnostic collects stimulated Brillouin scattering (SBS) UV light at around 351nm and stimulated Raman scattering (SRS) in the visible-light regime in the 420-720-nm-wavelength range and provides spectrally and temporally resolved information. Five 1-in. light collectors, composed of a lens, ground glass diffuser, and coupling into a 300-μm fiber, are positioned behind the last steering mirror on one of the four beamlines to catch a portion of the beam cross section (∼1.5%) of the emission that is scattered into the beamline. The SRS light is collected in two light collectors, combined, and transported via graded index fibers to a streaked spectrometer. The SABS-SRS streak spectrometer has a temporal and spectral resolution of 100ps and 1nm, respectively. Three other light collectors collect, combine, and transport the SBS signal to a Hamamatsu high-voltage photodiode, where an oscilloscope digitizes the data, providing a time resolution of better than 1ns. To obtain an absolute energy calibration of SRS measurements, light signals of known energy and wavelength were injected into the light collectors one at a time. The resulting counts on the streak camera charge-coupled device for SRS are then correlated with the incident fluence of scattered light at the light collector in order to allow a quantitative assessment of streak camera sensitivity to determine the energy of the scattered light during experiments. The measurements were performed in situ from the light collectors to the detectors. Additional offline measurements provided the transmission of the optics between the target chamber center and the light collectors.

Stimulated Brillouin scattering in optical fibers with end reflections excited by broadband pump waves

The transient theory of stimulated Brillouin scattering (SBS) in optical fibers is used to investigate the effects of weak feedback of incident broadband laser fields exhibiting different spectral shapes. The proper boundary conditions are given for the forward- and backward-propagating electric fields inside the fiber with a finite amount of reflectivity at the fiber ends. When the linewidth of the laser approaches the Brillouin frequency shift, a weak reflection of the laser field overlaps with the SBS gain and can be amplified in the fiber, resulting in an apparent reduction in SBS threshold. It is shown that the spectral shape of the incident field and its overlap with the SBS gain spectrum affects the SBS signal. Numerical examples are presented for incident laser fields that (1) simulate a pulsed, multilongitudinal-mode laser and (2) are a constant amplitude with a sinusoidal phase modulation. For the pulsed field with mode spacing much less than the Brillouin linewidth, calculations show that an end reflection of 0.01% (−40 dB) of the laser field with a linewidth equal to 0.75 of the Brillouin frequency shift can reduce the effective SBS threshold by a factor of 1.5. When the incident laser field is constant amplitude and phase modulated with a sinusoid, calculations predict sharp and distinct enhancement of the reflected power when the ratio of the Brillouin frequency shift to the modulation frequency is an integer for end reflections as low as 0.001% (−50 dB). Experiments performed with a sinusoidal phase modulated signal confirm the theoretical predictions. These results have implications on the design of high-power fiber laser systems that utilize spectral broadening to suppress SBS.

Investigation and modeling of optics damage in high-power laser systems caused by light backscattered in plasma at the target

High-power laser facilities may be restricted in operations by the risk of damage to optics due to the backscattering of laser light from the intended target. A portion of this backscattered light can re-enter the beam line and at sufficient fluence may damage (burn) optical apparatus. Here, the observed cumulative burn pattern on mirrors at the National Ignition Facility (NIF) due to stimulated Brillouin scattering (SBS) at the target is explained using detailed simulations. Our methodology involves using a measurement of a phase plate profile installed at the NIF to provide the laser input to a three-dimensional simulation of laser-plasma interaction in a target typical of that fielded at the NIF. Light scattered by SBS at the target is then followed back to the final aperture of the beam line, back through the phase plate, and to a mirror where damage typically occurs. We find that mirror damage patterns are largely dictated by the phase imprint of the phase plate on the returning SBS light. Our simulations show that the instantaneous SBS signal at the mirror varies on a picosecond time scale and is also highly modulated in space. Temporal averaging of the simulated SBS light pattern on the mirror reveals a pattern in close agreement with the experimentally observed damage. Understanding these burn patterns (distribution, modulation depth) may lead to future phase plate designs that limit damage throughout the optics assembly of high-powered laser facilities.

Tunable slow light via stimulated Brillouin scattering at 2 μm based on Tm-doped fiber amplifiers.

We present a slow light system based on stimulated Brillouin scattering (SBS) at 2 μm. A single-frequency fiber laser with Tm-doped fiber amplifiers was used to generate the SBS signal laser and the Brillouin pump light at 1.971 μm. The maximum delay time reaches 16 ns for pulses with 43-ns width, and the pulse width is broadened to 56.4 ns. The maximum delay time for 57-ns pulses reaches 33.4 ns, and the pulse width is broadened to 77.6 ns. The relative delays are 0.37 and 0.58 for 43 and 57 ns pulses, respectively. This is the first demonstration, as far as we know, on a slow light system at 2 μm, which may be substantial for future optical communications and LIDAR systems employing laser sources near 2-μm band.

Amplification of stimulated Brillouin scattering by collinear laser pulse series with two orthogonal polarizations

Using the characteristic that a time delay between the signal of stimulated Brillouin scattering （SBS） and the pump beam during amplification of SBS signal is allowed, a controller is devised to control the polarizations of two pulses propagating collinearly with orthogonal polarizations. It makes the two beams have the same polarization when the SBS signal meets the pump beam. Therefore, amplification of the SBS signal is realized.

Method for measuring the threshold value of stimulated Brillouin scattering in water

A new method for accurate measurement of the threshold value of stimulated Brillouin scattering (SBS) in water in terms of pump laser intensity is investigated. The threshold value of SBS is determined by the point of the deviation of the value of the attenuation coefficients of wide- and narrow-linewidth lasers rather than the intensity of the backscattered SBS signal in the material.

水下物体测量中受激布里渊散射过程的非线性光学特性

Nonlinear optical properties of stimulated Brillouin scattering (SBS) to signal detection in water are analyzed. With the threshold characteristics, SBS only occurs when the high power laser is focused in the SBS cell. When there is an object present in front of the focus, it leads to lower incident intensity and then SBS does not occur. The backward SBS signal depends on the focusing location. The nonlinear optical properties of SBS process in the focusing regime are analyzed theoretically. With the object coming near to the focusing center, the backward Stokes signal rises up from zero to a maximum, and then grows to saturation. The delay time of the echo signal to pump signal can give the object location. In experiment, the peak position of varying rate of energy can give object location.

Chaotic stimulated Brillouin scattering near the threshold in a fiber with feedback

We investigate a nonlinear dynamical behavior of the stimulated Brillouin scattering (SBS) near the threshold in the presence of feedback. When a cw Nd:YAG laser is injected into a single mode optical fiber, the SBS signal exhibits intermittently appearing irregular self-pulsations near the threshold. By examining the time series of the SBS signals, we verify that spontaneous Brillouin scattering having a stochastic property is dramatically suppressed due to the feedback. We explain the chaotic phenomenon of SBS in the presence of feedback in comparison with that in the absence of feedback.

Chaotic stimulated Brillouin scattering near the threshold in a fiber

We investigate the nonlinear dynamic behavior of stimulated Brillouin scattering (SBS) near threshold in the absence of feedback. When a cw Nd:YAG laser is injected into a single-mode optical fiber, the SBS signal exhibits intermittently appearing irregular self-pulsations near the threshold. By examining the time series of the SBS signals, we verify that the irregular SBS signal is one of the chaotic phenomena appearing near the bifurcation point.

A frequency-upshifting Brillouin enhanced four-wave mixing scheme using an iodine laser as a pump source

The characteristics of temporal modulation and frequency recovery in frequency-upshifting Brillouin-enhanced four-wave mixing (BEFWM) using CS 2 as a nonlinear medium were investigated experimentally for an iodine laser. BEFWM interaction in a stimulated Brillouin scattering (SBS) generator-amplifier scheme was tested, first, and compared with a new BEFWM scheme in which the amplifier cell is placed out of the beam path of the SBS signal originating from the generator cell, allowing a more efficient and more strongly compressed pulse. The output signal from BEFWM recovers the original laser frequency by frequency-upshifting a Stokes-shifted probe. A pulse compression from 50 ns to 3 ns between the incident laser pulse and the output signal and a power conversion efficiency of 30% with respect to the Stokes-shifted pump were obtained through BEFWM.

Stimulated Brillouin scattering in electrolytic solutions

An experimental investigation was made of the dependence of the power of stimulated Brillouin scattering (SBS) on the pump power and also of the dependence of the shift of the SBS components in several aqueous solutions of acids and salts on their concentration. The SBS gain was greatly affected even by low concentrations (of the order of a few percent by weight) and the change in gain altered the SBS signal amplitude by several orders of magnitude. The investigated salts reduced the gain, acids (with the exception of H2SO4) increased the gain, and sulfuric acid first increased and then strongly reduced the gain. The observed dependences could be explained by a change in the absorption of hypersound resulting from the frequency shift of relaxation processes of the dissociation-association type.

Stimulated Brillouin scattering in optical fibers

Observations of backward stimulated Brillouin scattering (SBS) in glass optical fibers are reported. Threshold for SBS has been achieved with less than 1 W of input power at 5355 Å. Relaxation behavior in the SBS signal has also been observed and is attributed to finite-cell-length oscillation. Experimental results are compared with theory, and the implied limitation to optical fiber transmission is discussed.