Dynamic laser control using feedback from a gain grating

We demonstrate that self-induced gain gratings can provide nonlinear optical feedback that results in single frequency selection and passive self Q-switching of a conventional linear laser cavity. An experimental Nd:YAG laser system is described that yields a temporally-smooth 20 ns pulse at 1.064 μm. In addition, we show that the feedback has phase-conjugate properties that permit “flower-like” mode formation even though the azimuthal symmetry of the cavity is broken     

Temporal dynamics of a ring dye laser with a stimulated Brillouin scattering mirror

We present a numerical study of the temporal dynamics of a stimulated Brillouin scattering ring resonator. A coaxial flash-lamp-pumped Rh6G dye laser is assumed. The influence of the most important parameters on the temporal evolution of the resonator is analyzed, namely, the acoustic decay time of the nonlinear material, the features of the external injection pulse - its pulse width, energy, and spatial quality - and the coupling mirror reflectivity. We found the conditions to initiate and maintain laser oscillation in the ring resonator as long as the duration of the pumping system pulse persisted.     

Experimental study of the propagation of an apertured high-intensity laser beam in Kerr-active CS2

Abstract

Transverse pattern formation along the propagation in Kerractive CS₂ of a circularly and an elliptically apertured high-intensity input beam is studied. Observation is made of the modification in the Fresnel diffraction pattern as a function of the input beam power and the propagation distance. In addition to the well defined ring patterns, at high powers these rings break up into several spots. Also, a thermal-induced nonlinearity was observed to affect the dynamics of the pattern formation. Both forward stimulated Raman scattering (SRS) and backward stimulated Brillouin scattering were observed to occur during the propagation of the beam along the CS₂ cell. An unexpected pattern of fringes was always observed in the Stokes components of the SRS.     

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

Abstract

Small signal and light induced absorption data taken at 633 nm and 1.06 μm 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 N _D, the total amount of rhodium in each sample. It is shown that the values of N _D 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 N _D.     

Efficient operation of a solid-state adaptive laser oscillator

We present the results of a cw diode-pumped Nd:YVO4 laser oscillator based on a self-starting adaptive gain-grating resonator. Adaptive laser operation has been demonstrated with 12-W output for 37 W of diode pumping, producing a TEM00 mode that compensates for thermal aberrations. The issue of the finite aperture of the amplifier is discussed, and a design that incorporates an intracavity lens is used to improve the collection efficiency with severe thermal lensing at high pump powers. The powers of the beams involved in the resonator are compared with theory and are found to be in good agreement. Spectral and temporal behavior of the adaptive laser is investigated, and very interesting behavior is shown, including self-induced temporal modulation dynamics and a switching between a narrowband and a broad bandwidth of operation.     

Direct measurement of the acoustic decay times of hypersonic waves generated by SBS

The acoustic decay time of hypersound generated by stimulated Brillouin scattering (SBS) has been measured in several heavy gases (Xe, SF6, CCIF3, C2F6) over a range of pressures. A straightforward optical probing technique is used whereby the decay time can be measured directly with high precision. A theoretical formulation of the decay mechanisms in a polyatomic gas is presented, and it is shown both theoretically and experimentally that vibrational relaxation can become the major decay process at high gas density. The Brillouin gain coefficient and acoustic frequency are also experimentally determined or calculated for the gases investigated. Two Brillouin-active gases (CCIF3and C2F6) with high Brillouin gains, which have not been studied previously, have been characterized. A study of the gas C2F6near its critical point showed a large variation of the acoustic velocity which reaches a minimum value in the vicinity of its critical density.     

High-intensity Effects in Self-pumped Photorefractive Phase Conjugation Using Nanosecond Pulses

Abstract

This paper reports on self-pumped photorefractive phase conjugation using repetitively pulsed high intensity (MW cm^?2) pulses of nanosecond duration. An intensity-dependent phase conjugate reflectivity is measured experimentally. In the corner self-pumped geometry the direction of beam fanning and corner self-pumping is observed to reverse above a critical intensity. Formation of a higher order spatial mode is reported for the external loop self-pumped geometry.     

Spectral filtering of gain gratings and spectral evolution ofholographic laser oscillators

We present results of the spectral filtering properties of volume gain gratings and their role as diffractive optical elements in the spectral evolution of holographic laser oscillators. We show that the gain grating acts as a spectral filter with a filter bandwidth that is approximately inversely proportional to the medium length. We investigate holographic laser oscillators and find that, when either the gain grating is written by monochromatic radiation or when it is initiated from broad-band radiation, the output of such oscillators can evolve to single longitudinal mode in correspondence to experimental observations