Hervé Gilles

Nanosecond pulse generation in a passively Q-switched Yb-doped fiber laser by Cr/sup 4+/:YAG saturable absorber

We explored efficient nanosecond pulse generation in a passively Q-switched cladding-pumped Yb-doped fiber laser by use of an external-cavity configuration containing a Cr/sup 4+/:YAG saturable absorber crystal. By exploiting passive Q-switched regime and stimulated Brillouin scattering, pulses of durations as short as 2.7 ns, corresponding to a peak power of /spl sim/9 kW, have been achieved. The laser was tunable over 70 nm and green output power generation was obtained by external frequency doubling in a KTP crystal.

Simple technique for measuring the Goos–Hänchen effect with polarization modulation and a position-sensitive detector

An original approach to directly measuring the Goos-Hänchen longitudinal shift between TE and TM polarization states during a total internal reflection is introduced. The technique is based on the modulation of the polarization state of a laser by an electro-optic modulator combined with a precise measurement of the resulting spatial displacement with a position-sensitive detector. This method presents many advantages over other techniques and allows measurements at different wavelengths over a broad range for the incident angle.

Goos-Hänchen and Imbert-Fedorov shifts for leaky guided modes

The Goos-Hanchen shift for a light beam totally reflected on the external interface of a dielectric thin film deposited on a high-index substrate can be strongly enhanced through some specific incidence angles corresponding to the leaky guided modes into the layer. Because the resonant eigenstates are polarization dependent, it has been possible to observe such resonance with an experimental setup based on a periodic modulation of the polarization state combined with position-sensitive detection. Classical models usually used for a single interface (Artmanns model based on phase argument and Renards model based on an energetic interpretation) have been re-adapted to describe the behavior of the entire layer. Good agreement is obtained between theory and experimental results.

Laser pumped 4He magnetometer

We describe the realization of a 4He magnetometer based on optical pumping with an optical frequency modulated laser diode light. Performances (amplitude and frequency spatial isotropy and sensitivity) of our device are presented and compared with those of other scalar magnetometers.

Observation of Ultra-narrow Electromagnetically Induced Transparency and Slow Light using Purely Electronic Spins in a Hot Atomic Vapor

Electromagnetically induced transparency (EIT) is observed in gaseous 4He at room temperature. Ultra-narrow (less than 10 kHz) EIT windows are obtained for the first time for purely electronic spins in the presence of Doppler broadening. The positive role of collisions is emphasized through measurements of the power dependence of the EIT resonance. The measurement of slow light opens up possible ways to applications.

Two-dimensional velocity measurements With self-mixing technique in diode-pumped Yb:Er glass laser

Self-mixing laser Doppler velocimeter based on a two beam geometry scheme is investigated using a single-frequency Yb:Er-doped phosphate glass laser. The geometry allows the observation of a beat mode with optical crosstalk between the two optical paths, giving two major improvements: 1) a precise positioning of the optical head compared to the scattering target; 2) the measurement of both the absolute value of the velocity and the orientation of the speed.

Near-field amplitude and phase measurements using heterodyne optical feedback on solid-state lasers

Heterodyne optical feedback on a solid-state laser is experimentally investigated as an efficient tool to characterize coherently near-field evanescent waves. A well-known topography of evanescent field is obtained via a total internal reflection of the light beam emitted by a class B Yb:Er glass laser. A subwavelength size optical fiber tip is scanned to locally probe the resulting evanescent wave in the near field. After a frequency shifting using a pair of acousto-optic modulators, the collected light is optically reinjected to excite the relaxation oscillations of the laser. The resulting dynamical response simultaneously allows very sensitive measurements of the amplitude and the phase of the evanescent wave. Extension of these preliminary results to near-field optical microscopy is suggested and discussed.

A new optical pumping scheme using a frequency modulated semi-conductor laser for 4He magnetometers

Abstract Recently, a distributed Bragg reflector (DBR) laser diode was developed by Spectra Diode Labs for helium optical pumping experiments. An interesting feature is the possibility of frequency modulation of the diode output by modulating the current intensity leading to a new pumping scheme, never reported before. An application to the realisation of very simple earth magnetometers without external modulators or external RF field is proposed.

Beat-note jitter suppression in a dual-frequency laser using optical feedback.

An efficient locking technique based on optical feedback is demonstrated to suppress jitter on the rf beat note between the two modes of a dual-frequency Yb:Er glass laser. The method consists of a self-injection process in which one selected mode serves as a master oscillator to lock and stabilize the second mode via a frequency-shifted optical feedback. The beat note adjusted near 170 MHz was stabilized with an accuracy of 250 mHz using an optical feedback loop with a double pass through an acousto-optic modulator. The beating note can be tuned over 300 kHz by controlling the reference oscillator. The extensions and limitations of the technique are discussed.

Optical Sensor for Real-Time Reconstruction of Distortions on Electronically Steered Antenna

A measurement system based on a set of optical fiber probes has been implemented and tested for real-time reconstruction of mechanical distortions of electronically steered antenna arrays. Such an optical sensor allows a full-reconstruction of the emitting surface topography, which is necessary to electronically compensate the degradation of the radiating pattern under mechanical distortions of its structure.