Sylvain Mailhot

Numerical procedure for the lateral-mode analysis of broad-area semiconductor lasers with an external cavity

A numerical procedure for the investigation of the lateral modes of semiconductor lasers with an external cavity is described. The propagation of the optical field inside the semiconductor laser is carried out via a standard beam-propagation scheme, while the method of coordinate scaling with the generalized Huygens-Fresnel integral allows for a computationally efficient propagation of the field in the external cavity. Using an eigenfunction solver based on the Prony method, it is shown that a simple external-cavity configuration comprising a broad area laser, a collimation lens, and a uniform end reflector can exhibit a complex modal behavior. Compared to a solitary broad area laser, optimized external cavities can yield enhanced modal discriminations, resulting in a single-lateral-mode operation with output power in excess of 100 mW along with a clean, single-lobed far-field pattern. The spatial-filtering action of the broad-area laser is highlighted, and we also discuss of the role played by the wavefront curvature of the beam incident upon the broad-area laser for achieving an efficient suppression of the higher order modes along with minimum increase of the threshold current. >

Noise reduction in a synchronously-pumped picosecond dye laser with a phase-conjugate mirror

Abstract Noise reduction by more than 35 dB in the megahertz range has been observedin a synchronously-pumped mode-locked dye laser with a phase-conjugating external cavity. The noise reduction is accompanied by a lengthening of the laser pulse. Both effects occur for external cavities shorter than the laser cavity and for a wide range of cavity detuning. The phase-conjugate mirror offers the advantages of self-alignment of the external cavity and the ease to measure exactly the effective feedback level.

Degenerate four-wave mixing in organic azo dyes chrysoidin and benzopurpurin 4B.

Phase-conjugate reflectivity obtained by degenerate four-wave mixing are measured in different azo dye solutions. A reflectivity up to 80% was achieved. Values of the nonlinear susceptibility chi((3)) are calculated, and its origin is discussed.

Noise reduction in mode-locked lasers with phase-conjugate feedback

External cavities terminated by a phase conjugate mirror have been used to provide a weak feedback to a synchronously pumped picosecond dye laser, a mode-locked argon ion laser and a continuous-wave argon ion laser. With the phase conjugate mirror, the external cavity is self-aligned and the reinjected field is best adapted to the intracavity field. Significant intensity noise reduction has been observed between 5 kHz and 1 GHz. For mode-locked lasers, it was possible to control the pulse length. These effects occur for wide ranges of cavity detuning and feedback level.

Lateral mode analysis of a broad-area laser operated with an external cavity

An analysis of the lateral-mode behavior of broad-area semiconductor lasers operating with a simple external-cavity configuration is presented. A numerical approach is employed for propagating the optical field around the external-cavity resonator, as well as for the calculation of realistic carrier-density profiles inside the active region of the broad-area laser. By slightly detuning the position of the laser relative to the collimation lens, it is shown that the lateral- mode selectivity can be significantly enhanced compared to that of a free-running broad-area laser. The lateral-mode selectivity and the shape of the far field radiation pattern emitted from the external mirror are found to depend heavily upon the separation between the external mirror and the collimation lens. The calculations also revealed that output powers of a few hundreds mW can be emitted in a single-lateral-mode output beam for configurations maximizing the lateral-mode selectivity.