MIRcat OPERATION
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D11-00028-02-A Page 48 of 54
9. Modulation Functions (CW)
Current Modulation
Unlike typical laser diodes, current modulation of a QCL generally does not produce a large change in
wavelength. Nevertheless, the MIRcat laser head includes an external Current Modulation input (BNC
socket) and associated internal circuity to allow external modulation of the QCL current at up to ~10% of
the nominal set value. This, produces Frequency Modulation (FM) and Amplitude Modulation (AM). The
ratio of FM to AM produced will depend on the laser wavelength set, namely where the laser is being
operated relative the peak of its gain curve. It is possible to achieve up to 100% AM modulation at some
places on the laser gain curve. Modulation is accomplished by applying up to a 4 V
pp
(sine wave) to the
Current Modulation input on the MIRcat laser head. Although QCL dependent, a typical transfer function for
applied modulation current is approximately 3.8 GHz pp modulation for 100 mA (38 MHz/mA). This level
of current modulation typically produces FM of ≥ 0.02 cm
-1
for modulation frequencies up to ~500 kHz.
Modulation Type Input to CW MIRcat laser
head
Connector
FM (with AM)* 0-4.0 V
pp
(± 2.0 V
pp
)
10 kHz – 500 kHz
BNC
*Ratio of FM to AM depends on laser wavelength
CAUTION: Applying a voltage higher than 4V
pp
to the BNC may result in damage
the warranty. Also use standard grounding precautions when
connecting to the modulation
input to prevent potentially damaging electrostatic discharge to the unit.
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