Quantum Instruments Cascade Laser Starter Kit - Manual (Page 24)

Starter Kit Instruction Manual Description 23
4.6.5 Laser peak voltage
The laser peak voltage is given by:
U
peak
= 2U LH − ULL
peak
where U LL
peak
is the corrected peak value of
ULL as calculated in the previous paragraph.
4.6.6 Average dissipation
The average thermal dissipation of the laser is given
by:
P = U
peak
I
peak
dc
where U
peak
and I
peak
are the peak values of
laser voltage and current as calculated in the pre-
vious paragraphs, and dc is the (corrected) duty
cycle.
4.6.7 Accuracy considerations
The duty cycle (corrected) is accurate to about 5%
for pulse lengths in the range 50ns to 150ns and
pulse periods in the range 1µs to 10µs. Especially
for short pulses, the accuracy can deteriorate to over
10%. These calculations and data are compared to
the pulse lengths measured via the BNC connec-
tor of the LDD100. The TTL pulses generated by
the TPG128 are always longer, due to losses in the
LDD100.
Since the other calculations depend on the duty
cycle data, they are in general even less accurate.
The rectifier circuits used to measure the peak volt-
ages show nonlinearities especially around 13V, and
therefore the voltage may seem to saturate at a
certain current for certain lasers. In addition, the
change in laser impedance around threshold can
generate remarkable nonlinearities compared to the
above calculations.
If you need accurate values, proceed as follows:
[1] Measure laser peak voltage, frequency and
duty cycle using a two-channel oscilloscope
(connected to the LEMO jacks of the LLH100)
in differential mode.
[2] Measure average current into the laser us-
ing the value given by the HV supply (or by
an attached RMS ampermeter).
[3] Calculate peak current by dividing average
current by the duty cycle.