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The VHE Q-Switch: Pushing the boundaries further
Q-Switching is a method frequently used to obtain short
laser pulses of enhanced power. However, improvements in laser
technology have lead to the situation where the maximum loss modulation
provided by conventional Q-Switches is insufficient to hold off the
laser output.
That was then: Alignment of two Q-Switches
For high-gain unpolarised systems, the Gooch & Housego
Super Q-Switch is available but until now, there was only one way to
provide the loss modulation needed to successfully Q-Switch high-gain
linearly-polarised systems. This was to fit two Q-Switches in series to
provide sequential depletion of the zeroth order beam. Orientation of
these two devices is crucial since any rediffraction of the first order
rays back into the zeroth order will significantly reduce the loss
modulation. Misalignment of the two Q-Switches could even result in a
lower loss modulation than a single Q-Switch on its own.
Rediffraction is not the only drawback associated with
using two Q-Switches. The relative phase of the acoustic modulation must
also be considered if timing jitter is to be avoided. The increase in
cavity length associated with fitting two Q-Switches will mean the pulse
width will be increased. Two Q-Switches will place four optical faces
into the laser cavity leading to increased insertion loss and multiple
reflections. Each of the two Q-Switches must be carefully aligned at the
Bragg angle while simultaneously avoiding rediffraction losses and of
course two Q-Switches will require extra plumbing for the water cooling
system and RF drivers.
This is now: A Q-Switch with >95% loss modulation
Understanding the challenges laser engineers face, Gooch
& Housego has developed the VHE Q-Switch. Designed for use in high-gain,
high-power, linearly-polarised Nd:YAG and Nd:YVO4 lasers, the
patent-pending design provides better than 95% single-pass loss
modulation, compared to ~85% from conventional designs. This outstanding
performance is achieved inside the industry-standard package which
allows simple integration into existing cavity configurations.
The rediffraction problem has been solved by careful
alignment of the acoustics within the structure. At certain incidence
angles, a laser beam will not be diffracted by an acoustic beam. These
angles are built into the VHE Q-Switch which ensures that light cannot
be diffracted back into the zeroth order.
This design greatly simplifies the alignment procedure
and simultaneously achieves >95% loss modulation. The VHE Q-Switch uses
a single RF driver so timing jitter from a phase mismatch between two
Q-Switches is eliminated.
The VHE Q-Switch from Gooch & Housego has been designed
to allow laser engineers to push the boundaries that little bit further. |
Fibre-coupled
AO Q-switch 
