Optimization and stabilization of external cavity diode laser with a constant output beam direction
Ngeno, Kipkirui Paul
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Tunable external cavity diode lasers has shown strong potential for various applications that require a high precision level than free running, commercially available diode lasers. Diode laser are better sources when power characteristic are important but not spectral properties. They operate in multimode, have broad line width for continuous wave (CW) laser, difficult to give specific wavelength since they are tuned by varying temperatures and current and suffer from mode hops. These spectral properties are undesirable in application areas where stability, durability, beam quality, tuning speed and range are vital. Researchers findings have shown that free running diode laser are sensitive to optical feedback. This idea is employed in this study where a compact external cavity diode laser adopting Littrow configuration shall be designed and implemented. The external cavity is wavelength selective. It is used to externally impose the desired wavelength. The external cavity consists of diode laser whose one facet is coated with antireflection (AR), a diffraction grating and a high quality optical mirror. The facet of the diode without antireflection CAR) coating increases the loss of the internal cavity, thus raising the threshold level required for lasing to start. The internal cavity is therefore prevented from lasing. The diffraction grating is used to provide an optical feedback to the diode laser. The grating splits an incident beam from the diode laser into diffraction orders such that the first order is reflected back to the laser diode while the zeroth order forms the output beam. Tuning will be achieved by controlling the angle of grating. The optical flat mirror allows tuning to be done without changing the direction of the output beam. Laser drive electronics will be designed to electrically pump the diode laser.