Fig. 1. (a) The gain medium and cavity end mirror are grown in a monolithic structure by the MOCVD technique. This figure shows the structure used in the present work designed for pumping at 808 nm and lasing at 970 nm. (b) Schematic of the laser cavity configuration used for the VECSEL work. The output from a fiber-coupled pump laser is focused onto the gain medium matching the spot size of the linear folded cavity. Heat is removed from the surface of the gain medium using a diamond heat spreader. This cavity geometry provides sufficient space for insertion of intra-cavity elements for single-frequency selection. A cavity mirror mounted on a piezo-electric transducer (PZT) allows electronic servo control of the cavity length for frequency stabilization.

Fig. 2. Output power as a function of pump power for basic VECSEL with no wavelength selecting intra-cavity elements. Both data sets taken with the gain medium at a temperature of 4° C and 10° C respectively show an initial slope efficiency of 33%. However, the thermal roll-over starts at a higher pump power for the low temperature data and hence a higher maximum power is achieved.

Fig. 3. The spatial profile of the output beam. (a): Normalized profile shown together with Gaussian fit with e^-2 radius ω₀. (b): False color image of beam profile.

Fig. 4. The VECSEL can be tuned by the insertion of a single-plate birefringent filter (BRF) into the cavity. The additional inclusion of an intra-cavity etalon ensures single longitudinal operation. The tuning ranges shown here is for a TEM₀₀ mode and limited by the free spectral range of the filter and not the gain bandwidth. The pump power is constant at 5.5 W.

Fig. 5. Frequency stability of the VECSEL. The insert shows the frequency deviation relative to a cavity as a function of time while the main figure provides a spectral analysis of this trace.