18|
3.0 Initial Setup
to the plane of incident polarisation. The direction of the white fiducial
mark on the half wave plate indicates the fast axis of the half wave plate
and thus can vary between 0-45 degrees.
Once experiments start you may increase the laser power to increase
signal levels by rotating the half wave plate slowly towards 0 degrees.
Power measurement is possible by means of a small <0.5% reflection
off of a coated optic onto a power meter. The optic is within a cage
cube directly after the intensity control module and the power meter is
screwed into the cage cube. The power meter control console can give
direct power measurement at a range of IR wavelengths.
The shutter is opened by a TTL signal generated by scanner control
software. It should be situated after the intensity control in order to
reduce laser damage. Typically the software opens and closes the
shutter at the beginning and end of an acquisition.
Typically, a
×
2 beam expander is supplied on the optical table to
increase the beam size at the entrance of the scanner.
3.3.2 Checking the alignment of the Scanhead galvanometers
After mechanically and electrically configuring the system, it is good
practice to check the alignment of the galvanometers.
If you suspect a large misalignment of the galvanometers i.e. no laser
beam coming through the objective please follow the procedure outlined
below.
The alignment pack contains a very bright (200 lm) LED
light source; please never look directly into the device
as this may cause eye damage.
Back alignment of system for nominal galvo alignment:
1. Make sure the galvo control box is plugged in and is switched
on, and that the scanners are connected to their respective
board and powered on. It is recommended that the control
voltage is set to zero, parking the galvos at their position of 45
degrees.
2. Place the LED and graticule from the alignment pack onto the
condenser arm graticule. Move the condenser arm up or down
using the Control Cube or Patchpad controller to focus the
graticule either on the ground glass disc provided or alignment
camera. Alternatively you may require the centre of the scan
field to be registered accurately with the particular CCD
camera/tube lens system. Make sure the potentiometer knob on
the LED controller is on a low power setting in order to avoid
saturation of camera pixels. It may be possible to view the
graticule on the camera through a small amount of light leaking
through the top turning mirror. To view the graticule on the
ground glass disc you must switch out the top turning mirror.
