Datasheet

Chapter B: Operations for advanced users

with increased bias current, due to the additional heating. This reduces the

number of lasers available for reaching a given emission wavelength.

CAUTION:

Applying a high bias current may destroy the laser due to thermal

roll-over. Bias-T setup must be performed by instructed personnel

and approved by ALPES LASERS.

• The optical output power must be monitored when setting up the bias-T to make

sure the thermal roll-over is not reached. Temporary increase of the pulse cur-

rent must always result in increased optical power output, otherwise the DC bias

current is already too high.

• As a rule of thumb, the overall dissipated power (sum of DC bias current dis-

sipation and pulse current dissipation) must never be higher than the average

dissipated power given by the highest current / voltage / temperature combina-

tion speciﬁed in the datasheet.

• The average dissipated power for a given pulse current I, pulse voltage U, and

duty cycle d is given by d × I × U, whereas the dissipated power due to a bias

current IB is given by IB × U. (U is the voltage on the laser, but it is safe for

this calculation of bias current dissipation to use the voltage on the LDD pulser

input.)

B.3.4. Gas concentration measurement

The goal of this procedure is to calibrate and optimize the laser spectrum as a function

of temperature and current. A spectral scan of the laser is generated over a wave-

length region deﬁned by the scan rate of the laser versus current (cm-1/A, a basic

property of the laser). A 60 mA range might be equivalent to 1.2 cm-1 of wavelength

change in the laser. The ALPES LASERS datasheets provide a few discrete settings

that were measured with a different equipment, which can be used as starting points,

but the curves obtained with the following procedure are to be used to acquire the real

gas data.

Prerequisites

• Using short pulses and "bias-T" to scan wavelengths

• User has appropriate short pulse generation electronics, cooler control/drive

electronics, gas cell(s) and photodetector

• User has and understands ALPES LASERS datasheets for the device to be used

102 QCL user’s manual v3.0