Incorrect operation of pulsed laser diodes often causes unnecessarily high rise times and voltage peaks that are damaging to the diode.
Ideal Driver: The LDP Series
The LDP-V series1 from our partner, PicoLAS, provides a comfortable driver, with which pulses in the range of <8 ns can typically be produced. The repetition rates lie in the MHz range; the duty cycle extends up to 5%. Currents from 0.3 A to 240 A and voltages up to 100 V can be produced. This only requires a voltage of 15 VDC and a trigger signal. The laser diode itself can be directly connected to the LDP-V.
Influences on the Rise Time
The rise time, t, of the laser diode is influenced by both the leakage inductance of the housing and the type of connection. The inductances, L, vary between 1.6 nH (Y package) and 12 nH (8-32 coaxial). The rise time can be estimated using the following formula:
t > = (L * I) / (0.9*U)
At an output voltage, U, of 100 V and an applied current, I, of 50 A, the rise time varies, for example, between 0.89 ns and 6.67 ns.
With connector cables, only the length and, if applicable, an additional twisting of the cables used are crucial. The forward and return conductors function like a coil in which induction occurs. Twisted cables intensify this effect.
L = N² x A / l
A length (forward and return conductors) of I = 100 mm, N = 10, and a space between the twisted cables of A = 0.0001 mm² would result in an inductance of L = 100 nH, and the pulse rise time would be increased by several 100 ns. If the laser diode were connected directly to the board with very small pins, the pulse rise time would only be increased by 3.5 ns.
The PLCS-20 Driver Module
For even greater convenience, the PLCS-20 driver module, equipped with an internal trigger source, can be attached. A microprocessor monitors the current, voltage, temperature, pulse duration, and repetition rate, and shuts the pulsed laser diode off autonomously if it detects an error. It is controlled using an RS-232 interface.
1 LDP-V XS, without a high voltage module, also available.
