John R. Thompson

Increased Stokes pulse energy variation from amplified classical noise in a fiber Raman generator.

We present an experimental and theoretical study of the transition from linear to nonlinear amplification of classical pump noise in a fiber Raman generator. In particular, we focus on the conversion of fluctuations in the fine temporal structure of Q-switched pump pulses into Stokes pulse energy fluctuations. We show that there is a distinct pump power domain where large scale fluctuations in the Stokes pulse energy result from the amplification of fluctuations in the temporal structure of pump pulses with stable energies. Dramatic changes in the shape of the Stokes pulse energy probability distribution also occur as the pump power is swept through the domain of large scale energy fluctuations.

A simple analytic model for noise shaping by an optical fiber Raman generator

Abstract An analytic model for first Stokes–Raman generation in optical fiber is used to evaluate the relative importance of quantum initiation noise and amplified classical pump noise in recent experiments on noise shaping. The model accounts for pump depletion and for fluctuations arising from the spontaneous generation of the first Stokes pulse, but not for scattering into higher-order Stokes pulses. The model reproduces the qualitative features of the measured first Stokes pulse energy statistics using realistic parameter values.

Influence of classical pump noise on long-pulse multiorder stimulated Raman scattering in optical fiber

We present a combined experimental and theoretical study of the effect of pump pulse noise on the growth and statistics of multiorder stimulated Raman scattering in optical fiber. Because of the intensity dependence of stimulated Raman scattering, fluctuations in the detailed temporal structure of the pump pulse amplitude strongly affect the growth and statistics of the Stokes orders, even when dispersive effects are not important. By comparing experimental results with a detailed model including the frequency dependence of the Raman gain and the pump pulse temporal structure, we show that the pump pulse temporal fluctuations play a pivotal role in determining the growth and pulse energy statistics of the Stokes orders.

First Stokes pulse energy statistics for cascade Raman generation in optical fiber

Abstract We present an experimental investigation of the pulse energy statistics of the first Stokes scattered light that is generated by spontaneous Raman scattering, and then amplified by stimulated scattering, for a wide range of input pump powers. We observe full-scale energy fluctuations for weak first Stokes scattering. The first Stokes pulse energy fluctuations diminish for strong scattering, and local noise minima mark the onset of higher-order Stokes scattering. We also present measurements of the correlation between the input pump and first Stokes pulse energies for a wide range of input pump powers. This correlation coefficient starts out small for weak first Stokes scattering, then increases as the first Stokes pulse grows in energy, and the sharply decreases as the pump is depleted by the generation of multiple Stokes orders.

Effects of pump pulse temporal structure on long-pulse multi-order stimulated Raman scattering in optical fiber

We present an experimental and theoretical investigation of the effects of pump pulse temporal structure on cascade Raman generation in the quasi-continuous wave regime. The growth and saturation of the Stokes pulse energies depend very strongly on the pump pulse temporal envelope and substructure. Experiments and simulations on the growth of the total Stokes pulse energy and the energy in a narrow central slice highlight the importance of knowing the detailed pump pulse temporal structure. Experimentally measured growth curves for different Stokes orders could be transformed by a simple scaling to lie on a universal curve.

Prelase stabilization of the polarization state and frequency of a Q-switched, diode-pumped, Nd:YAG laser

We present an experimental investigation of the energy statistics of the linear polarization components of pulses from a Nd:YAG laser that is repetitively Q-switched with an acousto-optic modulator. Varying the modulator-induced diffraction losses leads to changes in the pulse polarization state and the energy statistics of the polarization components. For conventional Q-switching there is no laser oscillation during the low-Q intervals, and we find that the orthogonal components of the pulses can display large relative energy fluctuations even though the total pulse energy is quite stable. In the prelase mode, a weak continuous-wave background seeds the Q-switched pulses and results in the emission of highly linearly polarized, single-longitudinal-mode pulses with small relative energy fluctuations.

Polarization control of a Q-switched, diode-pumped Nd:YAG laser.

We describe control of the polarization state of a diode-pumped Nd:YAG laser that is Q switched with an acousto-optic modulator (AOM). One of two orthogonal linear polarization states can be made dominant, depending on the amount of loss introduced by the AOM. Heterodyne beating indicates that the two polarization states are of slightly different frequencies.

Timing Jitter in Prelase-Initiated, Single-Mode Pulses from a Repetitively Q-Switched, Diode-Pumped, Nd:YAG Laser

Single-mode pulses from an Nd:YAG laser display substantial timing jitter relative to the opening of the Q-switch, which is driven by prelase intensity fluctuations proximate to the opening of the Q-switch.

The Roles of Intrinsic and Technical Noise in Pulsed Stimulated Brillouin Scattering in Optical Fiber

We present energy statistics of light generated by spontaneously initiated Stimulated Brillouin scattering driven by stable and fluctuating pump pulses. The distribution and amplitude of pump fluctuations are controlled to probe effects of technical noise.