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Chapter 1 – Fundamentals of Medical/Aesthetic Lasers and IPLs v1.2
Q-switched Lasers
In the early 1980s a Q-switched ruby laser was first tested to see if it could successfully remove tattoos. This laser was chosen because it can output relatively high energies in very short pulses.
So, what is a Q-switch?
Basically, a Q-switch is an optical device which is designed to effectively ‘shorten’ the length of the energy pulse generated by the laser. In a flashlamp-pumped laser, the pulse duration will be very close to the duration of the flashlamp pulse. Typically, this will be in the milliseconds regime.
Figure 27: A typical layout for a Q-switched laser
The light energy generated in the crystal is essentially ‘stored’ in the Q-switch. Once a certain threshold is achieved all of the energy is released in a very short timescale, usually in the nanosecond regime.
The Q-switch is a device which ‘forces’ a relatively long pulse into a much shorter pulse. There are two types of Q-switch – active and passive (learn more about Q-switching here).
Active Q-switches versus Passive Q-switches
Q-switches can come in a variety of guises, depending on the laser cavity design. Larger systems tend to use ‘active’ Q-switches, while the cheaper, smaller models will typically employ a ‘passive’ version. They both do the same job – just in a different manner.
Mike wrote a blog post on this topic a while ago – click here. The world’s first commercial Q- switched laser for tattoo removal was launched by Mike’s first company – DermaLase Limited – in 1990.
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Chapter 1 LEVEL A Fundamentals of Lasers/IPLs
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