Stimulated Brillouin Scattering Mirror Research Articles

Effect of pump mode structure on reflectance of SBS mirrors

In this paper, we have studied a two pass amplifier with a single and two-cell stimulated Brillouin scattering (SBS) phase conjugating mirrors. The role of longitudinal mode structure on the energy reflectivity of the SBS process and temporal behavior of the reflected pulse has been investigated experimentally. The results for different mode structures including single, double and multi-mode pump pulse for SBS mirrors with single and two cells are compared to each other. Our results show that the two cell SBS mirror has some new advantages over the single cell configuration when the laser oscillator operates in multi-mode regime. We found higher reflectivity at high entrance energy for backwardly amplified Stokes pulse. The mode beating become considerably smaller and fluctuations of Stokes pulse are smoothed in the SBS amplifier.

Stimulated Brillouin scattering phase conjugation of light beams carrying orbit angular momentum (Invited Paper)

We investigate the stimulated Brillouin scattering (SBS) properties of light beams carrying orbit angular momentum (OAM). The phase conjugation of light beams carrying OAM is experimentally achieved in an SBS mirror with a random phase plate. The spectrum and the pulse width compression of SBS light are measured. It is shown that the phenomena of pulse compression is observed and OAM conservation is confirmed in the SBS process. The OAM transfer from photons to phonons may find potential applications in photon-phonon conversion-based signal-processing schemes by using OAM multiplexing.

Control of the phase characteristics of Stokes waves in a Michelson interferometer with SBS mirrors

It is found that, when using stimulated Brillouin scattering (SBS) mirrors (mounted in a ring Michelson interferometer) with counterfocusing, under pumping by pulses with steep leading edges and applying Freon FC-75 as an active medium, the phase difference of the Stokes waves on the semitransparent interferometer mirror obeys the dependence ( is the difference in the magnitudes of the pump and Stokes component wave vectors and is the difference in the optical arm lengths).

Performance of Stimulated Brillouin Scattering Used in Several Heavy Fluorocarbons Liquids and Perfluoropolyether Liquids

Heavy fluorocarbons and perfluoropolyether liquids are ideal media for high power stimulated Brillouin scattering experiments from ultraviolet to infrared laser. Stimulated Brillouin scattering (SBS) reflectivity and threshold of new SBS liquids were measured systematically at four wavelengths (1064,532,355 and 266nm). Fluorinert FC-72,-75,-77 and Galden HT-70,-135 exhibits high reflectivity of over 90% and excellent fidelity in phase conjugation for over 100mJ, 10ns optical pulse at 1064,532, and 355nm. Among them, FC-77 and HT-70 were found to be good candidates to replace FC-72,-75 liquids which previously were known to be a good SBS media up to now. Heavy fluorocarbons and perfluoropolyether liquids are most promising as a phase conjugate SBS mirror for all solid-state high-energy lasers because of its high damage threshold and low absorbance.

Investigation of the impact of SBS-parameters and loss modulation on the mode locking of an SBS-laser oscillator

A Nd:YAG laser oscillator Q-switched and mode locked via a nonlinear mirror based on stimulated Brillouin scattering (SBS) and aided by an acousto optical modulator (AOM) has been realised. A rate equation model and a round trip model are used to describe the longitudinal mode dynamics. Parameter variations of the nonlinear SBS mirror and the loss modulating AOM in the resonator are investigated with regard to their effect on the pulse duration and spectra of the pulses.

About the correction of laser beams with phase front vortex

The earlier predicted failure of phase conjugation at the stimulated Brillouin scattering (SBS) of the vortex laser beam directly focused into the SBS medium is experimentally confirmed. Phase conjugation of the vortex beam can be realized with using an advanced SBS mirror.

A mirror based on stimulated brillouin scattering with a double feedback loop in a laser cavity

The possibility of switching an external mirror based on stimulated Brillouin scattering (SBS) with a double feedback loop to a laser cavity is shown experimentally. A significant increase in the output laser power is obtained with conservation of the diffraction quality of the initial radiation. Experimental comparison with an ordinary SBS mirror, excited in a single pass through a nonlinear medium, is performed and the advantage in the energy parameters of the scheme with a double feedback loop is shown. The threshold characteristics of the SBS mirror under study are calculated and good agreement with the experimental data is obtained.

Nd:YAG laser with a stimulated Brillouin scattering mirror and variable pulse duration

Different ways of varying the output pulse duration in laser schemes comprising a powerful master oscillator, a multipass amplifier, and a stimulated Brillouin scattering (SBS) mirror are suggested and realized experimentally. Conditions are determined at which introduction of losses between a SBS mirror and an amplifier allow variation of the output pulse duration without any significant decrease in energy. The use of two different SBS media (SnCl4 and freon) allows construction of a laser where the output pulse duration is varied between 6 and 40 ns and the energy loss is no more than 30%.

Qswitch and longitudinal modes of a laser oscillator with a stimulated-Brillouin-scattering mirror

A hypersound wave grating generated by stimulated-Brillouin-scattering (SBS) is applied in a laser resonator as a nonlinear mirror. This self pumped SBS mirror can be used for a passive Q switching of the laser by operating it inside a starter cavity. The Q-switch energy and pulse duration can be varied with a neutral glass filter. The Q-switch mechanism is explained and the pulse energy is calculated. As a consequence of the Brillouin frequency shift such resonators show a special behavior of the longitudinal modes. The longitudinal modes and the corresponding pulse shape of such a laser are investigated experimentally as a function of the start resonator length and the position of the SBS mirror. The results are explained by a superposition of modes of the SBS resonator taking into account their phases. Finally, the spectrum of the longitudinal modes is shown to be time dependent. These investigations yield in design criteria for efficient application of SBS mirrors as a laser resonator mirror.

Control of the duration of output pulses from an Nd:YAG laser with a stimulated Brillouin scattering mirror

Methods for varying the duration of output pulses were proposed and implemented experimentally for lasers in the form of master oscillator — amplifier — stimulated Brillouin scattering (SBS) mirror systems. The conditions were found under which the introduction of losses into the radiation beam between the SBS mirror and the amplifier could alter considerably the pulse duration without a significant reduction in the output energy. The use of two different SBS media made it possible to construct a laser with the pulse duration variable from 6 to 40 ns at the expense of reducing the output energy by no more than 30%.

Investigation of distortions of the laser pulse profile in multipass amplifiers with a stimulated-Brillouin-scattering mirror

A simple qualitative model of beams focused stimulated Brillouin scattering (SBS), capable of providing a sufficiently accurate description of the Stokes pulse profile, was developed. The characteristics of deformation of a laser pulse during amplification in two-pass and four-pass amplifiers with an SBS mirror were investigated theoretically and experimentally for fully overlapping pulses. The influence of pumping and spontaneous emission was ignored. Approximate formulas were derived for determination of the duration of an output pulse and of its leading edge. The parameters required for the most effective control of the output pulse profile were determined.

27-W average output power with 1.2*DL beam quality from a single-rod Nd:YAG laser with phase-conjugating SBS mirror

The beam quality of a single-rod Nd:YAG laser with large mode volume was improved almost up to the diffraction limit by using a phase-conjugating mirror (PCM) based on stimulated Brillouin scattering (SBS). A new resonator design was used with sulfur hexafluoride as the SBS medium. The laser is Q-switched by the nonlinear reflectivity of the PCM. The stable fundamental mode operation and high efficiency via large mode volume was guaranteed by the combination of a highly selective aperture setup and the SBS mirror. The system exhibits a temporal burst structure of up to 50 Hz and a repetition rate of 11 kHz within the burst. The single Q-switch pulse showed a width of 42 ns. The energy, width, and repetition rate of the Q-switch pulses within the burst can be adjusted by varying the parameters of the laser system.

High-energy operation of a stimulated Brillouin scattering mirror in an l-Arginine phosphate monohydrate crystal

An organic l-Arginine phosphate monohydrate (LAP) crystal showed a much lower stimulated Brillouin scattering (SBS) threshold at 1.06-mum wavelength than fused silica and a higher SBS reflectivity of approximately 65%, which is limited because of its absorbance. The reason LAP crystal has a high damage threshold at Q -switched pulse operation is due to SBS backward reflectance. The LAP crystal is interesting not only as a frequency converter but also as a phase-conjugated SBS mirror for all solid-state high-energy lasers because of its high SBS gain coefficient.

Improvement of Solid State Laser Performance by Phase-Conjugation Mirror Using a LAP Crystal.

Organic L-Arginine Phosphate Monohydrate (LAP) crystal showed much lower threshold (6mJ/18ns) stimulated Brillouin scattering (SBS) at 1.06μm wavelength than fused silica, and higher SBS reflectivity of approximately 65% (inherently 93%) limited due to its absorbance. The reason why LAP crystal has a high damage threshold at Q-switched pulse operation is explained due to the SBS backward reflectance. We have demostrated the improvement of wavefront distortion induced by thermal effects in solid-state laser materials. Deuterated LAP crystal is very interesting not only as a frequency converter but also as a phase conjugated SBS mirror for all solid-state high-energy lasers because of high SBS gain coefficient and its low absorbance.

Formation of high-quality XeCl laser radiation in a cavity with an SBS mirror

An experimental investigation was made of a XeCl laser with a cavity formed by a semitransparent plane mirror and a stimulated-Brillouin-scattering (SBS) medium. Spatial and spectral selection by the SBS mirror resulted in the formation of narrow-band highly directional radiation representing a superposition of converging and diverging beams. Each beam was amplitude-modulated at intervals of time corresponding to two round trips through the cavity and it consisted of a set of spectral lines 0.3 cm-1 wide, distributed over an interval of two SBS frequency shifts. About 30% of the energy of each beam was within the diffraction angle. The total output energy was 10 mJ when the pulse duration was 120 ns.

On the improvement of broadband stimulated Brillouin scattering reflectors

Stimulated Brillouin scattering (SBS) of unmodified XeCl laser radiation in n-hexane was investigated for building phase-conjugating mirrors. It was found that the SBS mirror reflectivity could be improved by setting a holographic grating in front of the SBS mirror and by using the first order beam reflected by the grating to pump the Brillouin medium. Maximum energy and power reflectivities of 45% and 80%, respectively, were measured. The SBS mirror energy reflectivity was reduced by 45% by removing the grating. The phase conjugation fidelity of the backscattered radiation was close to one, with or without the grating.

Realization of associative memory with the aid of a nonlinear selective stimulated-Brillouin-scattering mirror

An associative memory using only optical elements has been realized experimentally. The key element of the arrangement is a stimulated-Brillouin-scattering (SBS) selector consisting of a short SBS medium at the focus of a lens. The qualitative advantage of the selector over an SBS mirror is demonstrated experimentally. The response time of the arrangement is ∼ 10−8 s and is determined by the duration of the SBS. Estimates show that the SBS selector is capable in practice of distinguishing a signal against background noise when the initial distortion level of the object beam is 10−3. Reliable operation of the SBS selector has been demonstrated for radiative and energy loads reaching 2 GW/cm2 and 2 J, respectively.

Experimental study of a broad-band XeCl double-pass amplifier with SBS mirror

An oscillator-amplifier XeCl laser system has been used to experimentally investigate the effectiveness of a liquid stimulated Brillouin scattering (SBS) mirror for correcting the spatial aberrations of broad-band laser radiation in a double-pass amplifier. It has been found that the SBS amplifier performance is strongly dependent on the intensity Ip exciting the Brillouin medium. A good beam reconstruction has been attained at Ip≤1GW/cm2, whereas highly aberrated output beams have been delivered by the SBS amplifier for Ip>1 GW/cm2. By comparing the broad-band SBS amplifier performance to that of the same amplifier with a dielectrically coated flat mirror at one end, it has been found that the use of a SBS mirror is advantageous to obtain lower divergence output beams only for low energy pump beams (<1 mJ).

Experimental and theoretical investigation of two-cell stimulated-Brillouin-scattering systems

The use of a two-cell stimulated-Brillouin-scattering (SBS) system to extend the dynamic-power range of a phase-conjugate mirror is investigated experimentally and theoretically. A pulsed, frequency-doubled Nd:YAG laser system is used to study the SBS generator–amplifier arrangement, and the results demonstrate an increase in the achievable efficiency and dynamic-power range of the SBS mirror compared with a single-cell system while maintaining good phase-conjugate fidelity for a near-diffraction-limited beam. A full transient numerical modeling of the system is also presented, together with steady-state calculations for comparison. The technique of generator–amplifier geometries is applicable to other forms of stimulated scattering, including stimulated photorefractive scattering.

Stimulated Brillouin scattering of a KrF laser

A series of experiments in which the efficiency and fidelity of SBS (stimulated Brillouin scattering) wavefront reconstruction are measured as a function of the temporal coherence, focusing geometry, and power of the laser source is described. The primary motivation of the research is to assess the potential of SBS as the basis of a high-resolution image protection system. Thus, a series of high-resolution image projection experiments using a SBS mirror is also described. It is shown that provided that the coherent length of the laser is longer than the active focal region primarily responsible for the growth of the SBS wave, high SBS reflectivities can be obtained which are independent of the Rayleigh range of the focusing system used. In addition, wavefront reconstruction fidelities having values approaching unity can be observed when using laser powers near the threshold for the SBS process. >