Peter A. Roos

Laser vibrometer based on optical-feedback-induced frequency modulation of a single-mode laser diode.

We describe a sensitive and inexpensive vibrometer based on optical feedback by diffuse scattering to a single-mode diode laser. Fluctuations in the diode lasers operating frequency that are due to scattered light from a vibrating surface are used to detect the amplitude and frequency of surface vibrations. An additional physical vibration of the laser provides an absolute amplitude calibration. The fundamental bandwidth is determined by the laser response time of roughly 10(-9)s. A noise floor of 0.23 nm/Hz(1/2) at 30 kHz with 5 × 10(-5) of the incident light returning is demonstrated. This instrument provides an inexpensive and sensitive method of noncontact measurement in solid materials with low or uneven reflectivity. It can be used as a vibration or velocity sensor.

Solid-state carrier-envelope phase stabilization via quantum interference control of injected photocurrents

We demonstrate carrier-envelope phase stabilization of a mode-locked Ti:sapphire laser by use of quantum interference control of injected photocurrents in a semiconductor. No harmonic generation is required for this stabilization technique. Instead, interference between coexisting single- and two-photon absorption pathways in the semiconductor provides a phase comparison between different spectral components. The phase comparison, and the detection of the photocurrent that it produces, both occur within a single low-temperature-grown gallium arsenide sample. The carrier-envelope offset beat note fidelity is 30 dB in a 10-kHz resolution bandwidth. The out-of-loop phase-noise level is essentially identical to the best previous measurements with the standard self-referencing technique.

Characterization of quantum interference control of injected currents in LT-GaAs for carrier-envelope phase measurements

We use two mutually coherent, harmonically related pulse trains to experimentally characterize quantum interference control (QIC) of injected currents in low-temperature-grown gallium arsenide. We observe real-time QIC interference fringes, optimize the QIC signal fidelity, uncover critical signal dependences regarding beam spatial position on the sample, measure signal dependences on the fundamental and second harmonic average optical powers, and demonstrate signal characteristics that depend on the focused beam spot sizes. Following directly from our motivation for this study, we propose an initial experiment to measure and ultimately control the carrier-envelope phase evolution of a single octave-spanning pulse train using the QIC phenomenon.

Characterization of carrier-envelope phase-sensitive photocurrent injection in a semiconductor

We characterize the manner in which the carrier-envelope phase of ultrashort pulses can control quantum interference of injected photocurrents in low-temperature-grown gallium arsenide. We verify the predicted linear and square-root dependences of the generated current on the average optical powers of the low (nu) and high (2nu) frequency wings of a pulse spectrum, respectively. When scanning the time delay between these two colors, the signal amplitude exhibits a temporal width of 72 fs. The generated signal behaves as an ideal current source for loads below ∼100 kOmega. This behavior allows us to increase the signal detection bandwidth from 25 kHz with a voltage amplifier to 830 kHz by use of a transimpedance amplifier; higher bandwidths are possible. We discuss how transimpedance amplification could also enable the quantum-interference photocurrent signal to be measured by use of materials with longer carrier lifetimes, such as intrinsic GaAs.

Electrical measurement of carrier population modulation by two-color coherent control

Two-color quantum interference control in a semiconductor results in a charge current or a modulation of the carrier population depending on the phase shift between an optical wave and its second harmonic. Population control requires certain polarizations for the two colors with respect to the crystal axes. The authors present results of an electrical measurement of quantum interference control of charge carrier population in (111) oriented GaAs. The dependence of the population control signal on power, light polarization, bias, and laser spot position is studied.

Solid-state carrier-envelope-phase noise measurements with intrinsically balanced detection.

We use interference between single- and two-photon photocurrent generation pathways in a semiconductor to measure the out-of-loop carrier-envelope-phase noise of a stabilized Ti:sapphire modelocked laser. This solid-state measurement technique exhibits no significant amplitude/phase coupling, adds no measurable phase noise compared to the standard self-referencing technique, and requires few optical components. The method features a built-in balanced detection mechanism that is particularly appealing for dc carrier-envelope-phase measurements.

Doppler-induced unidirectional operation of a continuous-wave Raman ring laser in H 2

We demonstrate stable operation of a diode-pumped cw Raman ring laser in diatomic hydrogen gas. Doppler-induced asymmetry between the the forward and the backward Raman gains leads to inherent unidirectional operation in the forward direction without intracavity optical elements. Use of the ring-cavity geometry dilutes the deleterious effects of thermal lensing and significantly reduces optical feedback to the pump laser.

High conversion efficiency diode-pumped CW Raman laser

Summary form only given. The nonresonant CW Raman laser utilizing high-finesse cavity (HFC) enhancement is a recent development for laser frequency down-conversion. Several different experiments have been demonstrated using H/sub 2/ gas as the Raman gain medium. In all these demonstrated systems, the front and back mirrors in the HFCs were identical, resulting in an impedance-matched cavity only below threshold. Consequently photon conversion efficiencies for these systems did not exceed 35%.

Carrier-envelope phase stabilization using single-pulse coherent control in a semiconductor

We demonstrate carrier-envelope phase stabilization of a mode-locked Ti:sapphire laser using the phase-dependent photocurrent that results from interfering single- and two-photon quantum pathways in low-temperature-grown gallium arsenide.

Solid-State Carrier-Envelope Offset Frequency Detection Via Quantum Interference in Semconductors

We detect the carrier-envelope offset frequency of ultrashort optical pulses using quantum interference control of injected photocurrents in low-temperature-grown gallium arsenide. With further improvements to the signal fidelity, this solid-state detection method will enable stabilization of the carrier-envelope offset frequency of femtosecond modelocked laser pulses for optical frequency metrology