Eyesafe optical parametric system pumped by solid state lasers

Details Eyesafe optical parametric system pumped by solid state lasers Eyesafe optical parametric system pumped by solid state lasers

1998-09-25

2000-02-29

Scott, Jr., Leon

Coherent light generators

Particular beam control device

Nonlinear device

372 98, 372 92, 359330, H01S 310

Patent

active

060318538

DESCRIPTION:

BRIEF SUMMARY
TECHNICAL FIELD

This invention relates to the generation of an eyesafe laser beam with wavelength conversion in an optical parametric system.


BACKGROUND ART

A system of this kind is disclosed in U.S. Pat. No. 5,181,211 to Burnham et al, which works from the reported understanding that laser beams having a wavelength in the range of 1.5 .mu.m to 2.2 .mu.m are completely absorbed by the vitreous humor of the eye cornea, thereby avoiding any damage to the retina. The patent proposes the combination of a solid state laser, such as a diode-pumped neodymium laser, with a non-linear crystal parametric converter in an associated resonant optical cavity. In order to ensure the highest efficiency of operation, the patent requires non-critical phase matching in that the incident beam from the laser is transmitted parallel to one of the principal axes of the converter crystal. The output beam is said to be polarised in a direction parallel to a second of the principal axes and the idler beam is polarised in a direction parallel to the third principal axis. A preferred non-linear crystal is potassium titanyl phosphate (KTP).
The present invention stems from an appreciation that, contrary to U.S. Pat. No. 5,181,211, beam propagation parallel to a principal axis is not necessary and that beam propagation at an angle with .+-.10.degree. with respect to a principal axis can achieve parametric oscillation with no significant degradation of efficiency. Beam propagation parallel to a principal axis is also very difficult to align. Moreover, if the beam propagation is specifically off-axis, the output wavelength of the parametric converter can be tuneable according to the offset angle. This offers much greater flexibility than the type proposed in U.S. Pat. No. 5,181,211.


DISCLOSURE OF THE INVENTION

The invention accordingly provides a solid state laser beam generating system comprising, in combination: wavelength range outside the eyesafe range 1.5 .mu.m to 1.8 .mu.m; and second beam having a wavelength within said eyesafe range; having three defined principal axes and said system is configured such that, in operation, said first beam travels in a direction offset from one of said principal axes by an angle greater than 2.degree..
Preferably, the solid state laser means is a diode-pumped neodymium laser and said offset angle is in the range 2.degree. to 10.degree., said offset angle is in the range of 2.degree. to 10.degree., depending on the output wavelength required. Preferred neodymium lasers are Nd:YAG and Nd:YVO.sub.4 lasers operating respectively at 1.0642 .mu.m and 1.0643 .mu.m. Other lasers which may be utilised include an Nd:YAP laser operating at 1.0726 .mu.m or 1.0795 .mu.m or an Nd:YLF laser operating at 1.047 .mu.m or 1.053 .mu.m.
The converter means is preferably an optical parametric system such as an optical parametric oscillator (OPO), optical parametric generator (OPG) or an optical parametric amplifier (OPA). The preferred non-linear element is a non-linear crystal and the preferred such crystal is potassium titanyl phosphate (KTP). The converter means can be either within the pump laser cavity (intracavity) or external to the pump laser cavity (extracavity)


BRIEF DESCRIPTION OF THE DRAWINGS

The drawing is a schematic diagram of an eyesafe solid state laser beam generating system according to the preferred embodiment of the invention.


BEST MODES FOR CARRYING OUT THE INVENTION

As shown in the drawing, the eyesafe laser beam generating system comprises a pump laser 1 such as a Nd:YAG laser pumped by diode array, which produces an output laser beam 2 having a wavelength of 1.0642 .mu.m. The beam 2 passes through energy condensing optics 3 of known type before passing to an optical parametric system 4.
The optical parametric system comprises mirrors 5,6 and a non-linear crystal 7 such as a KTP crystal.
The input beam 2 travels through the crystal at an offset angle of between 2.degree. and 10.degree. to a principal axis to provide an output in the eyesafe wavelength range of 1.5 .mu.m to 1.8 m. Th

REFERENCES:
patent: 5181211 (1993-01-01), Burnham et al.
patent: 5594592 (1997-01-01), Harlamoff et al.
patent: 5606453 (1997-02-01), Walling et al.
patent: 5781571 (1998-07-01), Nabors et al.
patent: 5841570 (1998-11-01), Velsko

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