Spectral density contrast in DPSS and ECD lasers for quantum and other narrow-linewidth applications


INTRODUCTION

With current endeavours in the UK and around the world to foster the development of new Quantum-based technologies (QT) to sense and detect previously unreachable interactions, such as underground structures and gas leakages, the generation of light sources with highly stabilised output wavelengths have become critical. Diode-pumped solid-state (DPSS) and external cavity diode (ECD) lasers are two of the ideal candidates for narrow linewidth single frequency generation.


This paper will discuss some of their spectral performance differences.


Current laser technologies are compared upon SWaP-C (size, weight, power & cost) figures.

FUNDAMENTALS

Laser operation is supported for multiple lasing modes with a given cavity geometry and lasing medium. The excitation from the pump source is therefore distributed amongst the supported modes. The first area of interest for narrow-linewidth lasers is therefore mode selection to ensure single longitudinal mode (SLM) operation.


In this case, the power in the lasing mode is proportional to the number of photons associated with the spectral position of that mode. While, the total power is given as the sum of the power stored in the lasing mode and the additional spontaneous terms.


The theoretical minimum linewidth or the intrinsic linewidth is given by the Schawlow-Townes limit: