MEASUREMENTS OF THE FREQUENCY STABILITY OF ULTRALOW THERMAL-EXPANSIONGLASS-CERAMIC OPTICAL CAVITY LASERS

This paper reports on a technique for providing a frequency-stabilized helium-neon gas laser by using inherently stable ultralow thermal exp ansion optical cavities. Four longitudinal monoblock cavity lasers wer e constructed and tested. These had their laser mirrors optically cont acted to the bulk material. A 1 mm diameter hole along the axis of the block served as the discharge channel with electrodes optically conta cted to the sides of the block. One of these lasers had a glass capill iary for the discharge channel. A fifth laser had a gain tube with Bre wster angle windows fixed in a Zerodur box with the mirrors contacted to the ends. The warm-up characteristics of the five different lasers have been obtained and a theoretical model using finite element analys is was developed to determine the thermal expansion during warm-up. Us ing this computer model the thermal expansion coefficient of the mater ial Zerodur was obtained. The results suggest that monoblock lasers ca n produce a free-running laser frequency stability of better than 10 M Hz and show a repeatable warm-up characteristic of 100 MHz frequency d rift.