parameters do I need to specify if I want to order a Q-Switch?
will need to specify the frequency, aperture, acoustic mode and the type
of water connector.
frequency should I use?
answer depends on your location. There are various regulatory bodies
(for example the ITU) that stipulate the maximum levels of RF radiation
that can be emitted in certain frequency bands. The Q-Switch drive
frequency is usually chosen to be within one of the permitted bands for
the country in which it will operate. Historically, 24.0MHz has been the
chosen frequency in the USA and Japan and 27.12MHz in Europe and
elsewhere. However, this has been less rigidly observed in recent years
and 27.12MHz is now used widely in the USA.
is the difference between clear aperture and active aperture?
clear aperture of a Q-Switch is defined by the size of the block of
silica in which the light and sound interact. For the QS24/27 Series the
minimum clear aperture is 9mm.
The active aperture is defined by the height of the acoustic beam inside
the silica block. This is the dimension that matters when specifying a
do I select the appropriate aperture for my application?
a rule of thumb, the active aperture of the Q-Switch should be the same
as the beam diameter of the laser at the point where the Q-Switch will
be located. If the gain of the laser is modest it may be possible to use
a Q-Switch with an active aperture one size smaller than the actual beam
diameter (e.g. a 3mm active aperture Q-Switch in a laser with a 4mm
diameter rod). This has the advantage of requiring lower RF drive power
(drive power scales linearly with active aperture), which means less
heat input and consequently greater efficiency and improved beam
quality. It may even mean a lower cost driver can be used. On the
downside, alignment of the Q-Switch in the cavity may be more critical.
acoustic mode would suit me best?
choice is between shear (S) mode and compressional (C) mode (also known
as longitudinal mode). If your laser is unpolarised you should choose
shear mode. For polarised systems better results (less RF power = lower
cost driver, less heat = better beam quality) will be obtained by using
a compressional mode Q-Switch.
water connector should I choose?
choice is between screw-on (S) connectors with a nut and olives which
grip the outside of the flexible tubing, and barbed (B) push-on
connectors, which grip the inside of the flexible tubing. There is
little to choose between the two and it usually depends what type of
pipe fitting is used as standard in the laser system. Overall the
push-on fittings are probably best because there is no danger of them
restricting the water flow. (The olives in the screw-on type can
constrict the soft-wall tubing usually used in laser systems.)
do I know that the Q-Switch is not over-heating?
Q-Switch is fitted with a thermal interlock. If, for example, the
cooling water fails it will shut down the driver when the temperature
reaches 50 degrees C, preventing damage to the Q-Switch.
is the optimum operating temperature of the Q-Switch?
temperature should be set slightly above ambient to prevent the
possibility of condensation forming on the optical surfaces of the
Q-Switch. Around 32 degrees C is typical. For optimum performance and
lifetime we do not recommend operating the Q-Switch at temperatures
above 40 degrees C.
do I select the appropriate RF driver for my application?
do I know that the QS24/27 Series Q-Switch is the best choice for my
call one of our engineers if you are in any doubt about which Q-Switch
to use. The QS24/27 Series Q-Switches are 'industry standard' devices
that have been developed and refined over many years. As a result they
are very reliable and because they are manufactured in large quantities
they are lower cost than some of the more specialised products we can
offer. Basically, if you have a lamp-pumped industrial or medical Nd:YAG
laser this is probably the Q-Switch for you. It is also suitable for the
latest generation of high-power industrial diode-pumped lasers.
am designing a compact laser and the QS24/27 Series Q-Switch is too
large. What should I do?
manufacture a range of standard compact Q-Switches that may be suitable
for your application. If not, we have considerable experience of
designing application-specific Q-Switches. We supply Q-switches to many
of the leading diode-pumped laser manufacturers and it is likely that we
will have a design that can easily be adapted to suit your requirements.
have a single-mode polarised laser. Will the QS24/27 Series Q-Switch be
You can use a compressional mode version with a small active aperture
(3mm or less). However, you may find that the integrated Q-switch, with
its integral RF driver is a more cost effective solution that also
offers performance advantages in terms of higher average Q-Switched
much laser power can I hold off?
depends on the design of your laser cavity, where the Q-Switch is placed
in it and so on. Hold-off is not a parameter of the Q-Switch alone, but
of the Q-Switch/laser combination. We can however determine the
extra-cavity loss modulation of the Q-Switch, which is a direct measure
of its effectiveness at blocking the laser beam.
have a high gain laser and need the maximum possible loss modulation.
How do I achieve this?
are two ways; by using two compressional mode Q-Switches in series and
orientated such that the acoustic beams are orthogonal to each other you
can obtain a high, polarisation insensitive, loss modulation with
minimum RF drive power. Also available is a newly developed Q-Switch
incorporating two orthogonal compressional mode transducers in a single
monolithic cell and mounted in one convenient housing. A dual channel RF
driver is available for both applications.
I trust the damage threshold quoted in the data sheet?
We periodically send a sample Q-Switch to a NIST certified test house to
have the optical damage threshold verified. G&H take the utmost care
in the polishing of the optical surfaces and in their preparation and
coating. All these operations are carried out in-house in order to have
total control of the process.