Modulation-Free Frequency Stabilization of a Diode Laser: Zeeman-Effect

Abstract

In interferometric precision length measurement, the laser diode, which is more powerful and more compact, is suitable for use as an alternative to the HeNe laser. Stabilization of the operating parameters of a laser diode allows relative frequency stabilities in the range of 1 · 10^-7 to be achieved for a short time [1]. Due to the spectral ageing of the diodes (> 1 · 10^-5/Jahr [2]), the long-term stabilities below 1 · 10^-7 required for precision length measurement can be achieved only using an external reference such as, for example, an absorption line or a material measure. High frequency stabilities are here reached conventionally by linking-up of the slightly modulated emission frequency with an atomic absorption line. The modulation prevents, however, high-resolution phase interpolation techniques from being used in interferometric length measurement and thus limits the uncertainty of measurement which could otherwise be achieved.