Temporal structure of stimulated-Brillouin-scattering reflectivity considering transversal-mode development

The time-resolved reflectivity of optical phase conjugation by stimulated Brillouin scattering ~SBS! is investigated both theoretically and experimentally. A three-dimensional and transient model of SBS is developed to compare the experimental and theoretical results. Noise initiation of the SBS process is included in the model to simulate the shot-to-shot variation in the reflectivity and the Stokes temporal profile.Shahraam Afshaarvahid, Axel Heuer, Ralf Menzel, and Jesper Munc

Laser pulse compression and phase conjugation by stimulated Brillouin scattering

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Self-adaptive laser resonators using degenerative four-wave mixing in a proximity-coupled side-pumped Nd:YVO₄ amplifier

Degenerate four-wave mixing (FWM) techniques used to produce self-adaptive laser resonator based on diffraction from a gain grating have shown considerable promise for correction of distortion in high-power solid-state laser systems. In these systems, the gain grating is formed by spatial hole burning caused by interference of coherent beams in the laser amplifier and modulation of the population inversion. The gain grating formation can be used for phase conjugation by using the amplifier in a four-wave mixing geometry, for self-pumped phase conjugation by using an input beam in a self-intersecting loop geometry and for formation of a self-starting adaptive oscillator by providing additional feedback from an output coupler and requiring no external optical input. Successful demonstrations of such a self-adaptive resonator have been performed recently in diode side-pumped Nd:YVO4 [1] whose operation is based on the very high reflectivities (>800%) [2] and more recently (>10,000%) of a gain grating formed in a diode-bar side-pumped NdYVO4, amplifier. This resonator has been shown to correct for severe distortions introduced inside the loop with a maximum output of ~7.2 W so far achieved. We will present results of increased resonator outputs by proximity-coupling of the pump diode straight to the FWM amplifier region resulting in higher gains, whereby the diode emitting facet is placed around 50 microns from the pump face of the amplifying crystal. Output powers of the order ~10 W should be achievable, and we will present modelling data for such proximity-coupled geometries

Continuous wave holographic laser resonators using degenerate four-wave mixing in a diode bar side-pumped Nd:YVO₄ amplifier

Degenerate four-wave mixing techniques used to produce self-adaptive laser resonators based on diffraction from a gain grating have shown considerable promise for correction of distortion in high-average-power solid-state laser systems, as well as for spectral and temporal control of the laser radiation [1-4]. In these systems, the gain grating is formed by spatial hole burning caused by interference of coherent beams in the laser amplifier and modulation of the population inversion. The gain grating formation can be used for phase conjugation by using the amplifier in a four-wave mixing geometry [2], for self-pumped phase conjugation by using an input beam in a self-intersecting loop geometry [3] and for formation of a self-starting adaptive oscillator by providing additional feedback from an output coupler and requiring no external optical input. Experimental demonstrations have been performed successfully in several laser systems including flashlamp-pumped and quasi-c.w. pumped neodymium-doped amplifiers [1,2], in laser-pumped titanium-doped sapphire [4] and CO2 lasers. We present for the first time, demonstration of a continuous-wave self-adaptive holographic laser resonator. The operation is based on the very high reflectivities (>800%) [5] and more recently (>10,000%) of a gain grating formed in a diode-bar side-pumped Nd:YVO4 amplifier. We have subsequently modelled the FWM interactions and have found good agreement with experimental results. This resonator has been shown to correct for severe phase distortions introduced inside the loop. An output of ~1 W has so far been achieved, future steps include an additional power amplifier incorporated into the resonator loop geometry to give an expected multi-watt operation with a midterm goal of 10 W

Application of the three-valence model of photorefraction to rhodium-doped barium titanate

Small signal and light induced absorption data taken at 633 nm and 1.06 ?m for different samples of rhodium-doped barium titanate (Rh : BaTiO3) have been analysed. These data have been used in conjunction with the three-valence model theory of photorefraction to determine ND, the total amount of rhodium in each sample. It is shown that the values of ND calculated at the two wavelengths for individual samples are inconsistent with each other, although no evidence for other impurities in the samples has been observed. This indicates that a more complex theory than the three-valence model is necessary to explain the photorefractive processes in Rh : BaTiO3, and that an additional photorefractive centre may not be sufficient to account for the observed discrepancies in ND

Coherent beam combining of self-adaptive lasers

The novel technique of phase conjugate self-organised coherent beam combination is reported. It is demonstrated that due to the spectral mode freedom of a phase conjugate self-adaptive laser that efficient "all-passive" combination of many high quality lasers can be achieved. Efficient combination (>92%) of two modules has been experimentally demonstrated to >30W in continuous wave operation. Recent results demonstrating pulsed operation are also reported

Performance of a continuous-wave self-adaptive gain-grating laser

Experimental and theoretical studies have shown that three-dimensional gain gratings, optically written in a saturable laser amplifier, can act as very efficient (>1000%) diffractive optical elements and, in a four-wave mixing (FWM) geometry, can produce extremely high phase-conjugate reflectivity. A further development in the use of gain gratings for phase conjugation has been the employment of loop schemes to obtain self-pumped phase conjugation (SPPC) with only one input beam required. In reality, these devices are actually a novel type of (holographic) laser where the feedback is provided by diffraction from an externally-written gain-grating hologram

Pulse control in a Q-switched Nd:YVO4 bounce geometry laser using a secondary cavity

A novel technique for obtaining enhanced control of pulsing parameters in a laser is described and implemented for the first time in a 1.1%Nd:YVO4 bounce geometry laser. The method uses a secondary laser cavity to control the gain in a Q-switched primary laser cavity and has enabled clean single-pulse Q-switched operation to be obtained across a repetition rate range of 1-800 kHz, where previously laser breakthrough had occurred below 150 kHz. Control of the pulse energy from the Q-switched laser is also demonstrated at a fixed repetition rate of 100 kHz by this technique

Phase conjugate non-reciprocal transmission in multimode optical fibres

Correction of modal dispersion of light transmitted through multimode optical fibres has been the subject of extensive research to date. At low optical powers photoconductive crystals are typically used to produce phase conjugate correction at the output end of the fibre in doublepass schemes [1]. Double-pass correction schemes vary in their approach to overcome the apparent problem that only one (the e-polarised) polarisation state of the scrambled output from the fibre, can undergo phase conjugate correction. We report the results of our study on the implementation of phase conjugate correction of modal distortion in highly multimode, (300 micron diameter), short (~1m) passive optical fibres using a non-polarisation preserving phase conjugation scheme [2] and its application to a non-reciprocal transmission element. Figure 1 shows a schematic of the set-up used to demonstrate phaseconjugate non-reciprocal transmission characteristics in multimode fibres. An initial vertically polarised Gaussian input beam from an Ar-ion laser is launched into fibre A where it becomes polarization and modally scrambled as it travels along fibre A's length. nie optical power coupled into fibre B, and hence the forward transmission factor is dependent on the distance, z, between fibres A and B. The field from fibre B is then sent to a NPPPC consisting of a self-pumped BaTiO3 crystal. Previous work has shown that the field reflected from such a NPPPC consists of a phase conjugate part which will all couple back from fibre B to A in the reverse direction and a non-phase conjugate part which will have the same transmission characteristics as the forward travelling wave leading to different transmissions for the forward and backward direction