Optical: systems and elements – Optical amplifier – Correction of deleterious effects
Patent
1995-12-19
1997-05-20
Moskowitz, Nelson
Optical: systems and elements
Optical amplifier
Correction of deleterious effects
359341, 359345, 359349, H01S 323
Patent
active
056317697
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to laser amplifiers, and in particular, laser systems in which an oscillator output is subjected to high amplification.
BACKGROUND OF THE INVENTION
The oscillator-amplifier configuration is a known alternative to the plain oscillator in the design of laser sources. In general, it is neither as efficient nor as straightforward as the plain oscillator configuration. It can however, offer a significant advantage where a low power laser source already exists; or where a low power oscillator offers desirable features of quality or control not easily obtainable within a high power oscillator.
A particular problem that arises with such systems is that with high enough overall gain, the amplifier can exhibit super-radiance i.e. can generate output power when no input signal is present. This power can be a significant fraction of the amplifier's maximum output. Furthermore, it will emerge from both the input and output ends of the amplifier. It is therefore essential that super-radiance should be controlled or removed in a practical high power amplifier.
SUMMARY OF THE INVENTION
It is an object of the present invention to avoid or minimize one or more of the above disadvantages and problems of previously known systems.
It has now been found that super-radiance can be controlled by introducing a second input laser beam into the high power amplifier, to bleed off power from the amplifier to reduce or eliminate any tendency for the amplifier to super-radiate and "convert" it into a more or less controllable form.
The present invention provides a laser amplification system comprising a laser radiation source for providing a main laser beam, a laser radiation amplifier for amplifying said main beam, and means for supplying a bleed laser beam to the laser radiation amplifier for amplification thereby at least when the main laser beam has a low or zero power value substantially to prevent super-radiance.
The present invention also provides a high power laser amplifier system having an oscillator and an amplifier for amplifying a main laser beam input originating from said oscillator, wherein there is provided a bleed laser beam generator means for supplying a bleed laser beam input to said amplifier during operation of the amplifier, at least when the main laser beam input has a low or zero power value, whereby in use of said laser amplifier system with small or zero main laser beam inputs, said bleed laser beam input extracts sufficient power from said amplifier substantially to prevent super-radiance.
Thus with a system of the present invention super-radiance in a high power laser amplifier may be substantially avoided in a simple and effective manner by inputting the bleed beam into the amplifier so as to be amplified thereby and produce an amplified bleed beam which can be suitably diverted or otherwise controlled--unlike super-radiance,--thereby allowing, inter alia, effective amplification of low power (main) laser beam inputs without the risk of producing potentially damaging output radiation resulting from super-radiance.
Whilst the laser beam source(s) will usually comprise an oscillator(s), other sources could in principle also be used e.g. a super-fluorescent source. It will also be understood that the invention may be used with various different laser systems producing laser beams within or outside the visible spectrum, including CO.sub.2 and YAG laser systems.
The present invention is also applicable to laser amplifiers having a wide range of power outputs but is particularly beneficial in relation to higher power amplifiers wherein super-radiance is a particular problem. The degree of the problem will depend on various factors such the particular application for which the laser is being used e.g. the particular material being cut by the laser beam and the sensitivity of the material to damage from a super-radiant laser beam; and the lasing medium. In general, particularly in the case of CO.sub.2 lasers, the laser amplification system of the inventio
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Moore Limited
Moskowitz Nelson
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