Laditelný polovodičový laser s externím rezonátorem

Josef Lazar, Ondřej Číp, Petr Jedlička

We present a design of a stable and tuneable semiconductor laser with an external cavity. It is designed for a single-frequency operation in the visible region of spectra close to the traditional 633 nm He-Ne laser. It offers up to 5 nm coarse and 0.1 nm continuous tuning range, several mW of output optical power and less than 0.5 MHz linewidth. An optical frequency standard employing this laser source was assembled and by means of stabilizing by a subdoppler absorption spectroscopy technique the frequency stability below 10-11 was achieved. The laser is intended also as a source for interferometry, profile and roughness measurements, and for laser absorption spectroscopy of gasses.

The extended-cavity semiconductor laser uses the technique of single optical frequency selection developed previously for dye lasers, some time ago the only lasers with a broadband amplifying media. The resonator of laser diode is here suppressed by antireflection coating. The mechanical design was led by an effort to achieve high mechanical stability and rigidity. The long-term stability of traditional standards is achieved by a feedback regulation of the laser wavelength which is derived from very narrow absorption spectral lines of various gasses. We also applied this technique with some modifications. The absorption medium we used was iodine vapour with a dense net of spectral lines in the visible region of spectra. Interferometric techniques exploiting the potential of frequency tuneability are under development.

Semiconductor lasers based on this principle may be assembled for any wavelength region where laser diodes are available (a wide range from infrared up to the red part of visible spectra in these days) and can deliver a laser source able to follow even very demanding requirements for linewidth and stability. The primary applications were oriented into the fundamental dimensional metrology.

The compact extended-cavity laser.