Coherent light generators – Particular resonant cavity – Specified cavity component
Reexamination Certificate
2000-01-13
2001-11-13
Font, Frank G. (Department: 2877)
Coherent light generators
Particular resonant cavity
Specified cavity component
C372S105000, C372S106000, C359S830000, C359S831000, C359S490020, C359S834000
Reexamination Certificate
active
06317450
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to compensators for laser systems. More specifically, the present invention relates to thermal birefringence compensators for laser rods employed in double pass laser systems.
2. Description of the Related Art
Correcting the thermal birefringence of a laser rod, upon a double pass of the rod, has been accomplished using a 45° Faraday rotator. However, use of a Faraday rotator has a number of disadvantages. First, Faraday rotators are large and expensive devices. Second, Faraday rotators often absorb at the operating wavelength of a laser amplifier. Third, Faraday rotators are easily damaged. Moreover, while Faraday rotators work fine at correcting a rod's thermal birefringence in a double pass amplifier, these rotators are difficult to implement in an oscillator.
In a polarization outcoupled (POC) laser oscillator, two Faraday rotators are necessary, one to correct the rod birefringence and the other to control the outcoupling fraction, which would be 100% otherwise.
Other inventions by this Applicant also assigned to Raytheon Company include:
“Reeder Rotator” (Ser. No. 09/483,254; Attorney Docket No. PD-R98093); “Reeder Rod” (Ser. No. 09/482,230; Attorney Docket No. PD-R98094); and “Waveplate Polarization Rotator” (Ser. No. 09/482,378; Attorney Docket No. PD-R98109). These applications are incorporated herein by reference.
What is needed is an optical device that corrects the thermal birefringence of a laser rod, upon a double pass of the rod. It would be beneficial if the postulated optical device were made entirely of reciprocal optics, i.e., waveplates and prisms. Moreover, it would be desirable if the postulated optical device advantageously could be used in both conventionally and polarization outcoupled oscillators and double pass amplifiers.
SUMMARY OF THE INVENTION
The need in the art is addressed by the compensator of the present invention which provides thermal birefringence compensation of a laser system having an optically pumped laser rod. The inventive compensator includes a total internal reflection (TIR) coated prism and a first quarter waveplate, in combination with a second quarter waveplate. The prism and the first quarter waveplate each have polarization properties similar to a mirror and provide a beam fold function. The second quarter waveplate is provided to compensate the birefringence of a laser rod upon a double pass of the rod. Preferably, the inventive compensator is an end reflector. Advantageously, the prism can be one of a Benson, i.e., a right angle roof, prism or a porro prism.
Moreover, a double pass laser system constructed in accordance with the present teachings can include a gain medium and a compensator optically coupled to the gain medium. In the preferred embodiment, the compensator includes a Benson prism, a first quarter waveplate with its principle axes aligned to the fold axis of the Benson prism, and a second quarter waveplate with its principle axes at 45°, to the fold axis of the Benson prism.
In an illustrative implementation, a double pass laser system is disclosed which includes a gain medium and a compensator optically coupled to the gain medium. Preferably, the compensator includes a Porro prism and a first quarter waveplate with its principle axis at 45° relative to the axis of the Porro prism. The total internal reflecting surfaces of the Porro prism are coated with a thin film to provide a 90° phase shift between s and p-polarizations upon reflection to provide the polarization-wise behavioral characteristics of a mirror.
REFERENCES:
patent: 4408334 (1983-10-01), Lundstrom
patent: 5504763 (1996-04-01), Bischel et al.
patent: 6198574 (2001-03-01), Hill
patent: WO 81 02224 A (1981-08-01), None
patent: WO 86 03066 A (1986-05-01), None
patent: WO 95 22187 A (1995-08-01), None
Alkov Leonard A.
Font Frank G.
Lenzen, Jr. Glenn H.
Raufer Colin M.
Raytheon Company
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