Gerald T. Moore

Frontiers of nonequilibrium statistical physics

This book presents information on the following topics: the approach to thermodynamic equilibrium (and other stationary states); physics as a meaning circuit; predictive statistical mechanics; bifurcation geometry in physics; quantum distribution functions in non-equilibrium statistical mechanics; positive and negative joint quantum distributions; three lectures on the foundations of quantum theory and quantum electrodynamics; how to make quantum mechanics look like a hidden-variable theory and vice versa; a classical model of EPR experiment with quantum mechanical correlations and Bell inequalities; reduction of the wavepacket; Maxwells Demon, Szilards engine and quantum measurements; experimental tests of Bells inequalities with pairs of low energy correlated photons; a general nonlinear evolution equation for irreversible conservative approach to stable equilibrium; equation of motion for correlation function of strongly-coupled plasma; the one-atom maser; squeezed states; symmetry breaking in nonlinear optics; entropy, information and quantum geometry; phase transitions in nonequilibrium systems: dye lasers and lasers with saturable absorbers; and nonequilibrium phenomena at incommensurate phase transitions.

High-gain small-signal modes of the free-electron laser

Abstract The small-signal regime of the free-electron laser is analyzed for single-frequency, uniform-wiggler operation, taking diffraction into account. Exponentially growing modes are found with profiles independent of the longitudinal coordinate. Maximum gain occurs for a positive value of the energy detuning, though the gain on resonance is nearly maximal. If the current transverse distribution is uniform and sharp-edged, analytic solutions are obtained in terms of Bessel and Hankel functions with complex arguments. Positive energy detuning broadens the laser modes, while negative detuning concentrates them within the electron beam.

The high-gain regime of the free electron laser

The main emphasis of this paper is on the role played by diffraction in the small-signal, high-gain regime of the FEL. The paper begins by reviewing the one-dimensional theory of the high-gain FEL. This is followed by an analysis of diffractive effects in an axisymmetric cw FEL. It is shown that exponentially growing modes exist which have a profile independent of the longitudinal coordinate. A dimensionless parameter a, which is proportional to the radius of the electron beam and independent of the interaction length, determines whether diffraction is important. For a > 20, one-dimensional theory gives the correct gain. For small a the lowest-order transverse mode has a gain substantially higher than the other modes. Maximum gain occurs for a positive value of the energy detuning, though the gain on resonance is nearly maximal. Positive energy detuning broadens the laser modes, while negative detuning concentrates them within the electron beam. The paper concludes with an appendix on small-signal pulse propagation in the FEL and its high-gain limit.

20 W of continuous-wave sodium D2 resonance radiation from sum-frequency generation with injection-locked lasers

A 20-W all-solid-state continuous-wave single-frequency source tuned to the sodium D2a line at 589.159 nm has been developed for adaptive optical systems. This source is based on sum-frequency mixing two injection-locked Nd:YAG lasers in lithium triborate in a doubly resonant external cavity. Injection locking the Nd:YAG lasers not only ensures single-frequency operation but also allows the use of a single rf local oscillator for Pound-Drever-Hall locking both the injection-slave and the sum-frequency cavities. We observe power-conversion efficiencies in excess of 55% and a linearly polarized diffraction-limited output tunable across the sodium D2 line (589.156 to 589.160 nm) with no change in output power and with high amplitude and pointing stability.

Soft X-Ray free-electron laser with a laser undulator

We discuss the possibility of building a free-electron laser in the spectral region of tens of nanometers using a high-power laser pulse as the undulator. Requirements on the electron beam emittance, brightness, and energy spread are derived. The possibility of operation at the quantum limit is considered. The reduction of the gain due to diffraction of the undulator pulse (the variable mass-shift effect) is investigated, and several ways in which it could be overcome are suggested. Examples are presented showing that the device is feasible with moderate advances in current electron injector technology. Such a device would not require a large accelerator for high electron energies, nor a long wiggler made of permanent magnets.

A theoretical study of transient stimulated Brillouin scattering in optical fibers seeded with phase-modulated light

Beam combining of phase-modulated kilowatt fiber amplifiers has generated considerable interest recently. We describe in the time domain how stimulated Brillouin scattering (SBS) is generated in an optical fiber under phase-modulated laser conditions, and we analyze different phase modulation techniques. The temporal and spatial evolutions of the acoustic phonon, laser, and Stokes fields are determined by solving the coupled three-wave interaction system. Numerical accuracy is verified through agreement with the analytical solution for the un-modulated case and through the standard photon conservation relation for counter-propagating optical fields. As a test for a modulated laser, a sinusoidal phase modulation is examined for a broad range of modulation amplitudes and frequencies. We show that, at high modulation frequencies, our simulations agree with the analytical results obtained from decomposing the optical power into its frequency components. At low modulation frequencies, there is a significant departure due to the appreciable cross talk among the laser and Stokes sidebands. We also examine SBS suppression for a white noise source and show significant departures for short fibers from analytically derived formulas. Finally, SBS suppression through the application of pseudo-random bit sequence modulation is examined for various patterns. It is shown that for a fiber length of 9 m the patterns at or near n=7 provide the best mitigation of SBS with suppression factors approaching 17 dB at a modulation frequency of 5 GHz.

Greater than 100% photon-conversion efficiency from an optical parametric oscillator with intracavity difference-frequency mixing

Using 100-ps Nd:YAG pump pulses, we synchronously pump an optical parametric oscillator with intracavity difference-frequency mixing (DFM) between the signal and the idler. The cavity is singly resonant at the signal frequency. The signal, idler, and difference wavelengths are near 1.5, 3.5, and 2.8 µm, respectively. Periodically poled lithium niobate is used for both interactions. Results show an 80% enhancement in the idler power-conversion efficiency and an idler photon-conversion efficiency of 110% when the DFM interaction is phase matched. Backconversion of the pump is suppressed when the DFM interaction is phase matched, and pump depletion increases from 65% to 79% at full pump power.

High-gain and large-diffraction regimes of the FEL

Abstract The scaling relations for high-gain and low-gain operation of the free electron laser are compared, taking diffraction into account. In the high-gain, small-signal regime the gain per pass increases exponentially with the interaction length. The gain per length, as well as the coefficient multiplying the exponential, are calculated for several values of electron energy spread. Maximal gain is obtained when the incident field is the complex conjugate of the amplifying mode. A general analysis of the paraxial equation in the large-diffraction regime is used to reduce the nonlinear FEL equations to a one-dimensional form.

Realization of a 50-watt facility-class sodium guidestar pump laser

A CW Na guidestar excitation source has been constructed and installed on the 3.5-m telescope at the Starfire Optical Range. This device is comprised of injection-locked Nd:YAG ring lasers operating at 1064 nm and 1319 nm and a doubly resonant cavity where sum-frequency generation of these wavelengths in LBO produces a diffraction-limited linearly-polarized 589-nm beam. Up to 50 W of 589-nm light for mesospheric guide-star generation has been produced. The injection-locked Nd:YAG lasers are capable of operating at up to 100 watts at 1064 nm and 60 watts at 1319 nm.

Hot spots in parametric fluorescence with a pump beam of finite cross section

The parametric fluorescence from a nonlinear crystal driven by a pump beam of finite cross section displays a hot spot in the angular and spectral distribution of the signal radiation. The hot spot in the signal radiation occurs where the pump and idler Poynting vectors are collinear. Similarly, a hot spot in the idler radiation is predicted when the pump and signal Poynting vectors are collinear. Signal photons entering the signal hotspot are generally not correlated in direction or frequency with idler photons entering the idler hot spot. We report experimental observation of the signal hot spot in a AgGaS/sub 2/ crystal pumped by a Nd:YAG laser and describe a theory developed to understand the phenomenon. Qualitative and quantitative comparisons of the theory and data show good agreement. >