Basic Concept

Without laser diodes, our daily life would have a significant lack of entertainment and telecommunication. Beside the printer technology in this area the diode laser was the enabler for fast internet connection and high quality CD; Diode lasers differ from most ��classical�� lasers in two distinct ways:
First they do not posses an inherently defined wavelength. Instead of two defined energy levels, the lasing transition occurs between two energy bands. Further, the pn junction defines the lasing volume, instead of the resonator in a classical laser.
The experiment introduces the laser diode and investigates the variation of the emitted laser wavelength versus temperature and current. The set-up consists of a digital slot-in module with a 20 mW pig-tailed laser diode and integrated Peltier cooler. The change in wavelength by varying the temperature of the laser diode is measured by means of an optical multichannel analyser (OMA). The typical shift is approx. 0.25 nm per �C. The temperature range of the diode laser controller can be varied from 10 to 40� C, which results in a shift of 7.5 nm.
The use of an oscilloscope is recommended to prevent the influence other light sources the measurements are carried out with modulated diode laser light.

Experimental Set-up

The laser diode is mounted inside the slot-in module and provides an optical fibre output which terminates on the front panel of the slot-in module. By means of a fibre patch cable, it is connected to a rotational stage (CON) which allows the rotation perpendicular to the beam propagation to measure the spatial distribution of the emitted laser light. In front of the fibre telescope (FT-2), a pin hole is mounted. Via a second fibre patch cable, the detected light is fed to the photo detector slot-in module or to the OMA. The frequency generator or modulator is used to study the modulation capabilities of the laser diode with respect to its characteristic curve. Furhermore, it is used to modulate the laser diode with a rectangular signal in order to eliminate disturbing environmental light thus enhancing the sensitivity of the angle resolved intensity distribution of the used fibre patch cable.