Coherent light generators – Particular pumping means
Patent
1995-12-22
1997-11-25
Scott, Jr., Leon
Coherent light generators
Particular pumping means
372 25, 372 38, 372 92, H01S 309
Patent
active
056920040
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to lasers and has particular though not exclusive application to the construction and actuation of eye-safe laser devices.
BACKGROUND ART
In a known eye-safe laser assembly, an erbium glass rod of 75 mm length is pumped by a parallel flash lamp. The flash lamp power circuit includes one or more capacitive storage devices and a wound inductance in series with the lamp. The total weight of these assemblies, apart from any battery supply, is around 4 pounds (1.8 kg), a major contribution being from the inductance. The capacitors are typically also large in volume, and hence the flashlamp-pumped erbium glass configuration, although eye-safe and simple to operate, has limitations in application where small size and/or low weight are called for.
Another problem encountered with erbuim glass lasers is their susceptibility to thermal droop and the associated difficulty of achieving adequate control of their output energy within various limits. For a given energy input, E.sub.iN, erbium glass lasers exhibit a decaying energy outlet as the temperature of the rod increases with successive pulses, and the temperature impulse response of the rod for each pulse has a half-life of the order of 100 seconds. On the other hand, there is a minimum output threshold for adequate operation, typically around 4 mJ per pulse. There are also two upper thresholds--the legal limit for eye-safe operation typically 8 mJ per pulse) and a higher limit above which the laser is rendered non-functional by double pulsing. The problem was to achieve an adequate repetition rate at a desired output energy while applying input energy of the appropriate level without exceeding the legal limit and without incurring double pulsing.
A further problem associated with prior art flashlamp-pumped solid state lasers has been their fragility. Employment of such lasers in high vibration or high impact load applications is not possible because either the glass flashlamp or the laser material will break.
One approach to meeting some of problems associated with flashlamp-pumped pumped erbium glass eye-safe lasers has been to substitute diode pumping. Diode pumping has allowed elimination of the wound inductance, thus reducing the weight, has obviated the problem of double pulsing, and has proven more energy efficient than flash pumping. However, a much larger (in volume) capacitance is needed and a diode pump costs of the order of twenty times more than a flashlamp pump. Thus, while diode pumped erbium glass eye-safe lasers have been produced, these units have proven expensive and have remained relatively heavy and bulky.
Prior art admits that small active volumes with short (e.g. 30 mm) gain lengths can provide useful pulse outputs (e.g. 7 mJ in 30 ns from erbium glass), but it completely ignores the strength benefits of carefully selected dimensions for the "fragile" components. This is because prior art assumes universally that thermal droop must be compensated for solely by increasing the gain length.
Prior art therefore overcame thermal droop by making the laser longer. This renders it more fragile, and requires more energy, lacking in passive LC pump networks which are bulky, heavy, electrically inefficient, and optically inefficient (because current density is not controlled).
SUMMARY OF THE INVENTION
It is an object of the invention to provide a laser assembly which is adaptable to the economic production of an eye-safe laser assemble that is lighter, stronger, more robust and preferably also less bulky than eye-safe lasers hitherto available.
It has been realised that a preferred embodiment of a lighter, stronger, more efficient, smaller, and less expensive eye-safe laser can be obtained by initially considering the following points: excluding thermal droop, is preferably less than 100 mm.sup.3 40 to 60 mm. length is reduced for a given thickness. When the length/thickness ratio is less than 10, the crystal will withstand 100 g shock if correctly supported. for a given wall thickness. than conventi
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Electro Optic Systems Pty. Ltd.
Jr. Leon Scott
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