Do noncontingent interview mm-hmms facilitate interviewee productivity?

Two studies investigated the hypothesis that noncontingent interviewer "mmhmms" facilitate interviewee verbal productivity. In Study 1, 1 male interviewer interviewed 48 female undergraduates. In Study 2, 3 male interviewers interviewed 24 male undergraduates, and 3 female interviewers interviewed 24 female undergraduates. Within- and between-S comparisons did not support the hypothesis, although interviewees' ratings indicated that the mm-hmms were perceived as the social reinforcers they were intended to be. (15 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A comparison of the Cassegrain and other beam expanders in high-power pulsed dye lasers

We have constructed and compared high peak power YAG-pumped dye lasers using a variety of beam expansion methods, particularly the Cassegrainian telescope, grazing-incidence, and achromaticprism beam expander designs. We find that the Cassegrainian design offers a modest advantage over the conventional Hänsch or refractive telescope design in larger magnification and hence, narrower linewidth, while retaining several inherent drawbacks in cost, alignment difficulty, and amplified spontaneous emission (ASE) problems. New problems specific to the Cassegrainian design in high-power operation include limited wavelength range of the telescope secondary and a severe diffraction grating damage mechanism during alignment. We conclude that, on the whole, the Hänsch and Cassegrainian designs offer roughly equal performance. By comparison, the grazing-incidence design offers significant advantages in cost, ease of alignment, and linewidth without an etalon, but with reductions in efficiency, power output, and in some cases, wavelength stability. Our final judgment is that for high-power multimode operation, the four-prism achromatic beam expander is generally superior to the other designs. For single-mode operation, however, the prism design is rivaled by several ingenious grazing-incidence variations.     

FM and AM mode locking of the homogeneous laser--Part I: Theory

A new general analysis for mode-locked operation of a homogeneously broadened laser with either internal phase (FM) or amplitude (AM) modulation is presented in this paper. In this analysis, a complex Gaussian pulse is followed through one pass around the laser cavity. Approximations are made to the line shape and modulation characteristics to keep the pulse Gaussian. After one round trip, a self-consistent solution is required. This yields simple analytic expressions for the pulse length, frequency chirp, and bandwidth of the mode-locked pulses. The analysis is further extended to include effects of detuning of the modulator, in which case analytical expressions are obtained for the phase shift of the pulse within the modulation cycle, the shift of the pulse spectrum off line center, the change in pulse length, and the change in power output. Numerical results for a typical Nd:YAG laser are given. In the case of the FM mode-locked laser it is found that there is a frequency chirp on the pulse and that this causes pulse compression and stretching when the modulator is detuned. Etalon effects and dispersion effects are also considered.     

Interviewer specificity in seminaturalistic interviews.

Attempted to replicate earlier findings by B. Pope and A. W. Siegman (see PA, Vol. 39:13386, and Vol. 40:509) that there is an inverse relationship between interviewer specificity and both interviewee productivity and uncertainty, through the use of more naturalistic interviewers. 24 18-40 yr. old psychiatric inpatients were interviewed 3 times in a low specificity, high specificity, and an uncontrolled interview. Previous findings were supported. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Optical-Kerr-enhanced mode locking of a lamp-pumped Nd:YAG laser

We discuss the potential use of three new mode-locking techniques, namely additive-pulse mode locking, the combination of self-phase modulation and group velocity dispersion, and Kerr lens mode locking, as simple retrofits to enhance the performance of conventional multi-watt lamp-pumped Nd:YAG lasers. Of the three, we discard the APM technique because of structural and power-handling difficulties. We then discuss theoretically and confirm experimentally that the combination of SPM plus gain dispersion can lead to pulsewidth reduction by a factor of 2 to 2.5 but not more, in agreement with the analysis of Haus and Silberberg. Finally, while KLM can be very effective as a fast saturable absorber in many types of lasers, we find that its application to lamp-pumped YAG lasers is frustrated by instabilities in thermal focusing and transverse mode position characteristic of this type of laser     

Measurement of laser quantum frequency fluctuations using aPound-Drever stabilization system

We describe a method for measuring the frequency fluctuation spectrum of a laser oscillator, especially the weak noise contributions in the wings of the spectrum, and apply this method to confirm the existence of large excess quantum frequency fluctuations in a laser oscillator using an unstable optical resonator. Our measurement apparatus uses the Pound-Drever technique, which employs an RF phase modulator and a Fabry-Perot cavity to produce a sensitive high-speed frequency discrimination signal. We show that this signal can also be used to measure the quantum noise contributions to the frequency spectrum of a laser oscillator. Experimental measurements on a miniature diode-pumped Nd:YAG laser using a stable optical cavity closely match the predictions of the usual Schawlow-Townes theory, while the frequency fluctuations in a nearly identical laser employing an unstable optical resonator are approximately 1300 times larger. These much larger fluctuations arise in part from the larger output coupling and cavity bandwidth of the unstable cavity, but they also appear to confirm a predicted excess spontaneous emission factor (Petermann excess noise factor) of ≈180 times arising from the nonorthogonal transverse mode properties of the unstable cavity     

Laser induced photoacoustic grating effects in molecular crystals

A transient grating of singlet electronic excited states is produced in a pentacene-doped p-terphenyl molecular crystal by optical absorption from two crossed time-coincident picosecond excitation pulses at 532 nm. The diffraction properties of this volume grating are probed by a weak, variably delayed, Bragg-matched picosecond probe pulse. At high excitation intensities, a strong oscillatory behavior in the time-dependent scattering efficiency is observed superimposed on the exponential decay pattern of the excited-state grating. We attribute the oscillatory behavior to a thermal grating which induces coherent microwave acoustic phonons. These in turn modulate, at the sound frequency, the optical absorption properties of the pentacene molecules in the excited state. An acoustically induced amplitude grating effect is thus obtained, in contrast to conventional acousto-optic phase grating effects.     

FM-laser operation of the Nd:YAG laser

The FM-laser or frequency-sweeping mode of laser oscillation has been demonstrated in a Nd :YAG 1.06-μ laser with an intracavity LiNbO3phase modulator. The experimental results are in excellent agreement with the theoretical expressionDelta= (DeltaOmega/Deltanu) (delta/pi)where δ= peak single-pass phase retardation in the modulator,DeltaOmega= axial mode spacing,Deltanu=modulator detuning, and Δ=resulting FM index of the laser output. Modulation indices as large asDelta approx 230rad have been obtained, in which case the instantaneous laser frequency is sweeping over a full spectral range of2Delta cdot f_{m} approx 120GHz (≈ 4 cm^-1) at a repetition frequencyf_{m} approx 260MHz, with a time-bandwidth product per periodapprox 2Delta approx 460. The coherently mode-locked spectral bandwidth thus obtained in the FM-laser case is very much wider than can be achieved in the pulsed mode-locked case with the same Nd:YAG laser. Some possible ways of using this broad-band coherent FM spectrum are suggested.