Direct measurement of the spectral reflectance of OP-SDL gain elements under optical pumping

Carl Borgentun,Jörgen Bengtsson,Anders Larsson

doi:10.1364/oe.19.016890

Abstract

We report on a direct measurement method for acquiring highly precise reflectance spectra of gain elements for semiconductor disk lasers under optical pumping. The gain element acts as an active mirror, and the active mirror reflectance (AMR) was measured with a weak and tunable probe beam coincident on the gain element with a high-power pump beam. In particular, we measured the spectral AMR of a gain element designed to have a broad and flat AMR spectrum by being anti-resonant at the center wavelength and employing a parametrically optimized anti-reflection structure. We were able to confirm that this sophisticated gain element performs according to design, with an almost constant AMR of ∼103% over a wavelength range of nearly 35 nm, very well matching the simulated behavior. Such gain characteristics are useful for optically pumped semiconductor disk lasers (OP-SDLs) designed for broadband tuning and short-pulse generation through mode-locking. The measurement technique was also applied to a conventional resonant periodic gain element designed for fixed wavelength OP-SDL operation; its AMR spectrum is markedly different with a narrow peak, again in good agreement with the simulations.

Highlights

The optically pumped semiconductor disk laser (OP-SDL), or vertical-external-cavity surfaceemitting laser (VECSEL), is a laser capable of generating a high-power beam of almost diffraction-limited quality [1, 2]
We report on a direct measurement method for acquiring highly precise reflectance spectra of gain elements for semiconductor disk lasers under optical pumping
The measurement technique was applied to a conventional resonant periodic gain element designed for fixed wavelength OP-SDL operation; its active mirror reflectance (AMR) spectrum is markedly different with a narrow peak, again in good agreement with the simulations

Summary

Introduction

The optically pumped semiconductor disk laser (OP-SDL), or vertical-external-cavity surfaceemitting laser (VECSEL), is a laser capable of generating a high-power beam of almost diffraction-limited quality [1, 2]. A common way to experimentally test the design is to perform a spectral reflectance measurement in the absence of optical pumping, i.e. to measure the reflectance of a tunable probe beam incident on the ”non-active” GE [3]. This is a straight-forward measurement method but reveals little information on the actual performance of the GE under pump excitation. Other methods are based on measurements on the entire OP-SDL, including the external cavity, such as the pump threshold intensity measurements of a tunable OP-SDL in [4], and only provide indirect information on the spectral properties of the GE since cavity and saturation effects influence the measurements

Methods

Results

Conclusion