External Cavity Diode Laser Setup with Two Interference Filters

TL;DR

This paper describes a stable, narrow-linewidth external cavity diode laser setup at 450 nm using two interference filters and a locking scheme, achieving two-day single-frequency operation.

Contribution

Introduction of a dual interference filter setup with H"ansch-Couillaud locking for enhanced stability in blue diode lasers.

Findings

Narrower transmission width with increased edge steepness.

Stable single-frequency operation over two days.

Effective locking scheme improves laser stability.

Abstract

We present an external cavity diode laser setup using two identical, commercially available interference filters operated in the blue wavelength range around 450 nm. The combination of the two filters decreases the transmission width, while increasing the edge steepness without a significant reduction in peak transmittance. Due to the broad spectral transmission of such interference filters compared to the internal mode spacing of blue laser diodes, an additional locking scheme, based on H\"ansch-Couillaud locking to a cavity, has been added to improve the stability. The laser is stabilized to a line in the tellurium spectrum via saturation spectroscopy, and single-frequency operation for a duration of two days is demonstrated by monitoring the error signal of the lock and the piezo drive compensating the length change of the external resonator due to air pressure variations. Additionally, transmission curves of the filters and the spectra of a sample of diodes are given.