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In this work, we present DBR-TPL with an additional internal DBR-grating at the output side of the tapered amplifiersection in comparison with DBR-TPL with standard facet coating of different reflectivities.
Our DBR-TPLs are based on an epitaxial structure with a large and asymmetric waveguide to realize a small vertical far field for optimal coupling into SHG-crystals. All DBR-TPL consist of a 2 mm long ridge waveguide section, which contains a 1 mm long passive DBR-grating section at the end for longitudinal mode filtering. The amplifier-section is 4 mm long and forms a taper with a full angle of 6°.
The influence of the front mirror reflectivity on laser performance including reliability is investigated. The DBR-TPL emit up to 9 W of optical output power in continuous wave operation at 25°C in a longitudinal single mode at 1064 nm and yet the spectral width remains below 20 pm. In favor of a high radiance the power content in the central lobe at a total optical output power of 8 W is greater than 75% for almost all devices. Aging tests revealed significant differences in the lifetime of the devices depending on their front facet reflectivity or length of the front DBR-grating, respectively.
In this work, we present DBR-TPLs which are able to emit more than 10 W in continuous-wave operation with a narrow spectral emission at 1154 nm and a very good beam quality providing excellent spectral radiance. The investigated DBRTPLs are based on three different epitaxial structures with varying vertical far field angles of 35°, 26°, and 17°. To optimize the coupling efficiency into non-linear crystals we studied DBR-TPL with a vertical far field angle of approx. 17° based on an asymmetrical super large optical cavity epitaxial structure. At a pump current of 18 A these devices are able to emit more than 9 W at 25°C and nearly 11 W at 10°C. The spectral emission is very narrow (ΔλFWHM = 18 pm) and single mode over the entire current range. While the beam quality factor M2 according to the 1/e2-level remains 1.1, the M2 according to second order moments deteriorates when the laser is pumped with higher currents. Therefore, the power content in the central lobe increases somewhat less rapidly than the total power.
In our paper, we will present a further development of our red-emitting distributed Bragg reflector ridge waveguide laser (DBR-RWL). DBR surface gratings are implemented into the 2 mm long RWL by BCl3-Ar reactive ion etching. This fabrication process uses a single-epitaxy and is hence industry-compatible.
At a heat sink temperature of 15°C the DBR-RWL provides 120 mW of optical output power in longitudinal single mode emission. Heterodyne linewidth measurements of two identical DBR-RWL show a FWHM linewidth of less than 2 MHz. The excellent beam quality (M2 = 1.1) enables the use of these chips for play-back of holographic films or as master oscillators in a future micro-integrated master oscillator power amplifier configuration for recording.
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