Vidia-Discrete
General Operation • 21
2. Press the
Hi Res/Step
button once to initiate the scan (the laser will
stay tuned to the start wavelength).
3. Press the
Hi Res/Step
button to advance the laser to each step.
4. When the next step is past the stop wavelength, the laser will
automatically end the scan and return to the start wavelength.
Cancelling a Scan
To stop a scan, use computer control to abort the scan, or switch the
laser into track mode by pressing the
Track
button twice.
Modulating the Laser Output
Modulate the laser current (amplitude) using an externally generated
low-level signal. Connect the line for the input signal to the
Current
Modulation
connector on the back of the controller. Make sure the
signal conforms to the following specifications:
* For models with a serial number ending below 02000, the
impedance is 5 k
Ω
and the modulation is 0.2 mA/V.
The DC-coupled Current Modulation Input is NOT current limited. To prevent
damage to the laser diode DO NOT modulate the current with input voltages
above ±10 V.
Since changes in the current affect the laser frequency, modulating the current will
also create some fine-frequency modulation due to changes in the index of
refraction of the laser-gain medium. The degree to which this affects the laser is
wavelength dependent, but it is in the range of 25–40 MHz/mA.
Current Modulation Input Guidelines (DC-coupled)
Connector Type
BNC
Max. Voltage
±10 V
Input Frequency Range
10 kHz–1 MHz
Impedance
1 k
Ω
Modulation*
1 mA/V
Note:
Note:
64X7 rev E.fm Page 21 Tuesday, April 3, 2001 4:16 PM
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