M74050
1/4M IMAGING SPECTROGRAPHS
38
11 GRATING INSTALLATION AND CALIBRATION
Grating installation and field
calibration are typically performed at one of Newport’s manufacturing location,
or by qualified field service personnel. The instructions provided in this section are for advanced users
only.
11.1 RECALIBRATION SERVICES
Newport suggests that spectrographs be returned annually for service. In addition to verifying the
calibration, the instrument also undergoes full inspection. Any refurbishment required, such as fresh
lubrication on the worm gear, would be included during the recalibration of the instrument.
11.2 SETTING THE WAVELENGTH OFFSET
A wavelength offset is used to shift the wavelength position to either a higher or a lower wavelength.
For example, if a HeNe laser operating at 632.8 nm is sent through the spectrograph and the output
is visible when the spectrograph is set to 640 nm, an offset can be introduced.
When performing this procedure, it is necessary to use a light source with a known spectral line
appearing within the operating range of the grating. Oriel offers a number of pencil calibration lamps
for this purpose, such as the model 6035 Hg lamp. Another line source such as a laser may also
be used. Always be sure to follow the appropriate safety precautions when dealing with any light
source.
Procedure:
1. Select a radiation source that has at least one narrow spectral line in the wavelength
region of interest.
2. Select a detector with an operating range appropriate for the spectral line.
3. Focus the radiation onto the entrance slit (the spectrograph is F/3.9). Note that a
narrower slit provides greater resolution.
4. Ensure the focused beam is parallel to the spectrograph
’s optical axis.
5. Command the spectrograph to select the grating for which the offset is to be applied
to.
6. Use the STEP command to move the grating position until the spectral line is visible
at the output.
7. Use the CALIBRATE command to enter the exact wavelength of the spectral line.
The MS260i wavelength offset has now been entered into memory. This offset
applies to all other wavelength positions when using this grating.
8. Repeat the process for the second and third gratings, if required. Depending on the
configuration, the spectrograph may have two or three gratings installed.