The emergence of semiconductor manufacturing techniques has allowed diode lasers to permeate throughout our daily lives. Diode lasers can be found in devices ranging from the humble CD player to high end spectroscopic devices. The low cost of external cavity laser diodes has made them an extremely popular candidate for experiments in atomic and molecular spectroscopy. Semiconductors and by extension the diode laser have properties that are dependent on the excitation of electrons contained within the valence band to the conduction band. The temperature of the device has a direct influence on this process and is why precision temperature control is required. Building a classical proportional-derivative-integral (PID) controller for a thermoelectric cooler contained within the device is one such way to isolate the operating temperature to regions where the diode parameters are known. Issues arising from actuator and modeling must be resolved to achieve sufficient temperature control. The problem of laser control does not stop with temperature control, the diode output power needs to also be addressed as the introduction of electrons via the input current into the diode cavity alters the refractive index of the diode itself and by implication the output laser wavelength, in other words, for high power applications the laser wavelength changes. This project will construct both power and temperature controllers to enable the stable operation of the ALCATEL A1935LMI laser diode for a range of frequencies at a useable output power level. It is desired that the user will be able to input the desired frequency of operation. The eventual aim of having this controller implemented in the school of physics atom optics laboratory mandates that the controller be constructed for a minimal financial outlay, hence the decision to use classical control.

Associate Professor Peter Farrell, Adrian D'Alfonso