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Single Mode GaAs Laser in External Cavity

IP.com Disclosure Number: IPCOM000077355D
Original Publication Date: 1972-Jul-01
Included in the Prior Art Database: 2005-Feb-25
Document File: 2 page(s) / 27K

Publishing Venue

IBM

Related People

Ludeke, R: AUTHOR [+2]

Abstract

A single mode cw laser source in the 0.8-0.9 mu m spectral range and with output power levels of greater than 100 mw is a desirable tool for spectroscopic and, possibly, communications work, for which a highly monochromatic (halfwidth of the order of 100 MHz or smaller) source is presently not available.

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Single Mode GaAs Laser in External Cavity

A single mode cw laser source in the 0.8-0.9 mu m spectral range and with output power levels of greater than 100 mw is a desirable tool for spectroscopic and, possibly, communications work, for which a highly monochromatic (halfwidth of the order of 100 MHz or smaller) source is presently not available.

Such a source can be achieved through an arrangement illustrated in the figure, consisting of a GaAs diode 1, with a suitable antireflection coating 2, a lens 3 and a grating 4 mounted with its lower end flush with the lower end of lens
3.

Normally, the emitted radiation of such a device consists of several longitudinal and other modes simultaneously excited over a wavelength region delta lambda, determined by the spectral resolution of the grating. In order to achieve single-mode operation, the ratio delta lambda/delta lambda, where mode spacing of the external cavity modes, must be minimized. In particular, the condition for selection of a single-cavity mode is that delta lambda/delta lambda <
2.

It can be shown that delta lambda over delta lambda cot theta i + 1/2, with F, D, as specified in the figure.

The ratio F/D is simply the f/number of the lens, and its value of two is determined by the divergence angle of the beam of light emanating from diode 1. The condition for single-mode operation is satisfied for theta i>53 degrees. This angle specifies a grating of approximately 2000 lines/mm, which is well within the fa...