Final Report on VECSEL Optimization : VIGRE Summer 2007
نویسنده
چکیده
Vertical External Cavity Surface Emitting Lasers (VECSELs) are a type of laser that have been found to be useful in situations requiring high output power and pulses of short duration. The typical VECSEL is composed of (at least) two mirrors: the active or gain mirror where the light is amplified and reflected and an outcoupling mirror where some laser light is allowed to exit the laser. When one desires to create laser pulses rather than a continuous beam a third mirror is added, known as the passive mirror or SESAM (SEmiconductor Saturable Absorber Mirror). The design of the VECSEL with the SESAM is of particular interest due to its ability to deliver both very rapid (on the order of GHz) and high power (typically on the order of milli-Watts) pulses. Within the VECSEL these three mirrors are situated in a “V” shaped cavity, with the gain mirror occupying the lower portion of the “V” and the SESAM and outcoupling mirror situated at the other two ends—as it travels through the VECSEL, a pulse is reflected off the active mirror, the SESAM, and again off the gain mirror before returning to outcoupling mirror again [1] [5]. For the purposes of this paper, our focus will primarily on the active mirror and secondarily on the SESAM. Both the active and passive mirrors have a similar structure composed of two principle parts: the Distributed Bragg Reflector (DBR) and the Quantum Well Stack (there is only one quantum well in the SESAM, while there are multiple in the active mirror). The DBR is a periodic structure of reflective interfaces that cause the incoming light to be gradually reflected as it travels through the mirror, creating a very high quality reflector (often with reflectivity of more than 99.9% [6]) [4]. A constant percentage of the light is transmitted at each interface in the DBR, thus causing the intensity of the incoming light to decay exponentially as it travels into the DBR, and
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