Light Conversion ORPHEUS, Руководство пользователя

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ORPHEUS User’s Manual
32 support@lightcon.com Light Conversion
If the oscillator is off/not mode-locked/CW – the amplifier might deliver the same output power at
slightly higher pump currents for laser diode bars. The output of unseeded regenerative amplifier is of
nanosecond pulse duration and the intensity is too low to pump ORPHEUS. In such a case it is not possible
to have white light generation in ORPHEUS, generation of the second harmonic is inefficient. The easiest
way to identify unseeded operation of the amplifier is monitoring the photodiode of regenerating amplifier
with the oscilloscope: the build-up trace is different from normal cavity-round-trip incremental signals of
photodiode in seeded operation (see user’s manual of amplifier for more details).
Wavelength and spectral width affect calibration of ORPHEUS. Phase matching angle of the crystals is
a function of pump wavelength. If the change is even within 1 nm range – the angle might no longer be
optimal. If the central wavelength of the pump cannot be recovered – the alignment of harmonic crystals
and offsets (or even recalibration) for the tuning curves of ORPHEUS might be necessary.
Pulse contrast ratio also affects the pulse energy of “real” pulse. Only the most intense pulse takes
part in amplification. Pre-pulses and post-pulses reduce the efficiency of harmonic generation and more
energy is needed for white light generation. The contrast ratio can be checked with fast photodiode and an
oscilloscope. Please refer to the manual of pump laser on optimization of pulse contrast.
7.2 Resetting Motor Positions
Reset of motor positions may be necessary after an electrical failure or software issues. There is no
feedback from the rotation/translation stage to control card to monitor the exact position. The feedback –
reset switch – is only at the very beginning of total moving range of the stage. Reset procedure of the
motor double checks the absolute position of stage with respect to reset switch: the software rotates the
motor until the stage hits a microswitch button and then moves the stage to position at which it was left
from the software.
This procedure is performed by pressing a “Reset all ” button in the “ Motors ” section of WinTOPAS
software.
7.3 Input Beam Alignment
In case of pump laser alignment or a change in system layout, it may be necessary to re-introduce the
pump beam to ORPHEUS. This is performed by using alignment apertures (BT) inside ORPHEUS and special
beam alignment targets. The beam should travel through the center of these apertures. The positions
where to place the BTs when aligning the pump beam are shown in Figure 22.
Consult Light Conversion
support team (support@lightcon.com) first before performing any alignment.
Firstly, the beam should be centered on the iris A1 (marked by number 1 in the figure above) and on
the beam alignment target placed in the position marked by number 2. The correct procedure is to center
the beam on the iris by tuning the BRM1 mirror and then to center the beam on the target by tuning the
mirror BRM2. It may take several iterations to get the beam centered on both apertures.
NOTICE
Never use the full pump power to align the beam. Do not
close the A1 iris when ORPHEUS is operating at full
(nominal) power. This could result in damage of several
optical components in the beam path.