Optical: systems and elements – Optical amplifier
Reexamination Certificate
2000-02-15
2002-06-04
Hellner, Mark (Department: 3662)
Optical: systems and elements
Optical amplifier
C359S330000, C372S021000
Reexamination Certificate
active
06400495
ABSTRACT:
BACKGROUND OF THE INVENTION
Passively Q-switched microchip lasers are attractive light sources for applications requiring highly repeatable, high-peak-power pulses of short duration. Such devices are relatively simple to manufacture and are capable of withstanding substantial levels of vibrational and thermal shock. These laser devices have been most successfully implemented at output wavelengths near 1.0 &mgr;m. This is largely due to a lack of good combinations of gain media and saturable absorbers that support alternate wavelength outputs.
Many applications require a light source that operates in an eye-safe spectral region near 1.5 &mgr;m with short pulse duration and high peak power. There have been several attempts to construct such light sources using, for example, semiconductor saturable-absorber mirrors as passive Q switches for 1.5-&mgr;m lasers. Likewise, there have been attempts to develop 1.5-&mgr;m optical parametric devices pumped by 1-&mgr;m microchip lasers. Each of these approaches sacrifices some of the simplicity, robustness and cost advantage associated with the 1-&mgr;m passively Q-switched microchip laser.
SUMMARY
The present invention is generally directed towards a two-stage laser system including a passively Q-switched microchip laser and a gain-switched microchip laser. A pulse train generated by the passively Q-switched laser is fed into the gain-switched laser, which in turn produces an optical output signal at a preferred wavelength.
More particularly, the passively Q-switched laser of the present invention is pumped with an optical signal generated by, for example, a diode pump laser. Based on absorption of the optical signal, energy in the passively Q-switched laser then accumulates in its optical cavity until a threshold is reached. Thereafter, an output optical pulse, preferably at 1.064 &mgr;m, is produced. As mentioned, these optical pulses are then fed into the gain-switched laser.
In turn, energy accumulates in the optical cavity of the gain-switched laser where the gain medium absorbs the optical pulse from the Q-switched laser. Preferably, the gain medium is made from a YAG host doped with Cr
4+
ions, which have a large absorption cross section at 1.064 &mgr;m. As a result, light from the optical pulse efficiently inverts the transition near a second wavelength. This results in a gain in the gain-switched cavity at the second wavelength. By choosing an appropriate output coupler on the gain-switched laser, the gain induced by the absorbed 1.064-&mgr;m pulse leads to the development of an optical pulse at the second wavelength. Preferably, the output pulse at the second wavelength is at around 1.5 &mgr;m, which is an eye-safe wavelength.
The configuration of lasers in the present invention has many advantageous features not suggested by the prior art. For example, an eye-safe laser output is generated using a passively Q-switched laser coupled to a gain-switched laser. It is thus possible to use the laser system of the present invention in applications where there is a danger of laser-light exposure to the human eye. Additionally, the material used to construct the laser system of the present invention is capable of withstanding harsh environmental conditions such as vibrational and thermal shock. Furthermore, no high-speed control electronics or high voltages are required, in contrast to systems employing actively Q-switched lasers. Hence, the two-stage laser system is reliable and can be employed in many safety-critical applications.
Another advantageous feature of the laser system of the present invention is its overall construction. The material used to construct such a laser system is relatively inexpensive and the compound laser device itself is simple to manufacture. Such a laser system is therefore an attractive solution for many diverse low-budget applications.
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Hamilton Brook Smith & Reynolds P.C.
Hellner Mark
Massachusetts Institute of Technology
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