Continuously operating diode laser are available from a few milliwatt up to several hundreds of watt. They can also be operated in a pulsed mode, however the pulse power is slightly above the continuous power. Pulsed diode laser can only emit pulses but with extremely high peak power in the kilowatt range in a very short time of a couple of nanoseconds. Such diode laser are useful when a flash lamp like emission is required like for range finder, optical time domain reflectometer (OTDR) or light detection and ranging (LIDAR).
This experiment is equipped with a pulse diode laser emitting at 905 nm with a maximum peak power of 70W and a pulse width of 100 nanoseconds. Both, the peak power as well the pulse width can be adjusted within a certain range. The students will study the parameter by displaying the timely behaviour on a digital oscilloscope. The optical as well as electrical discharge pulse is monitored. The diode laser is operated by the discharge of a preloaded capacitor. The influence of the the charging voltage and discharge time on the emitted power is recorded and discussed.
The optical property of the diode laser like spatial beam distribution is measured and with subsequent collimation formed to an almost parallel beam. Further on the polarisation of the diode laser emission is measured using a polarisation analyser.
With an optical power meter the energy per pulse is measured in micro Joule. The energy sensor as well as display unit are optional and needs to be ordered extra.
The pulse laser diode requires an electrical pulse to emit a laser pulse. It cannot operate in cw mode like other laser diodes. Their advantage is that they can deliver a peak power which is magnitudes higher than the cw power. The electrical pulse is generated by discharging a capacitor (closing of the switch). The capacitor is charged (open switch) to the desired voltage Vc. The attached controller manages the charging cycles and sets the desired voltage Vc. The output peak power depends on the stored energy by the capacitor and the repetition rate on the ON/OFF rate of the switch.
The pulse laser diode is built into a round housing which is mounted into a twofold rotary stage for horizontal and coaxial rotation. This allows the measurement of the spatial intensity distribution of the emitted laser light. The incident light from the laser diode is detected and measured with a fixed photodetector. The polarisation property of the laser light is measured by placing a polarisation analyser in front of the fast photodetector. The detector is connected to a circuit which converts the photocurrent into a voltage which can be displayed on an oscilloscope to observe the dynamic parameter like repetition rate, pulse width and peak power. An optional energy meter is available which measures the energy of a single pulse. Using the pulse width, the optical peak power can be calculated.