High repetition rate pulsed laser

Details High repetition rate pulsed laser High repetition rate pulsed laser

1998-11-18

2001-06-12

Scott, Jr., Leon (Department: 2881)

Coherent light generators

Particular beam control device

Control of pulse characteristics

C372S098000, C372S102000, C372S022000, C372S020000

Reexamination Certificate

active

06246707

ABSTRACT:

FIELD OF THE INVENTION
The field of the invention concerns a pulsed solid state laser. In particular the invention relates to a method and apparatus for generating a pulsed solid state laser having a high conversion efficiency at a high repetition rate and narrow band width.
BACKGROUND OF THE INVENTION
Solid state laser operation at a high repetition rate is desired for many applications. However, obtaining sufficient power conversion and a narrow band width has been problematic in the past. Especially desirable is a solid state tunable laser which can be operated at a high repetition rate of 700 pulses per second or greater.
Prior art tunable lasers are known. For example, a Ti:Sapphire (Ti:Sapphire) laser having a repetition rate of 10 pulses per second is known in the art. See U.S. Pat. No. 5,121,398 (RAO). 3x beam expanders and a diffraction grating have been used in these types of devices.
However, there is still a need for pulsed lasers which can be operated at much higher repetition rates and having a narrow band width and a high power output.
SUMMARY OF THE INVENTION
According to the invention a pulsed solid state laser preferably a tunable laser having a narrow band width is provided which has a high conversion efficiency at a high repetition rate. In a further aspect of the invention, the solid state laser according to the invention has a high conversion efficiency at a high pump power. Preferably the laser according to the invention is at a pump power of 4 to 25 watts or more. In another aspect of the invention a method of operating a pulsed laser at a high repetition rate and narrow band width and preferably at a high pump power is provided. According to the invention, a diffraction grating is located in the laser's optical cavity. The optical cavity is defined by a mirror and diffraction grating or two mirrors with a diffraction grating therebetween. A laser material is located within the optical cavity between a mirror and the diffraction grating. Desirably the diffraction grating is movably mounted within the optical cavity so that a beam of a presected wavelength diffracted by the grating can be directed across the laser material along the optical axis. Optionally where two mirrors define the optical cavity, one or both of the mirrors and optionally the grating can be movably mounted within the optical cavity. Preferable the movable grating and the movable mirror are rotatably mounted.
A solid state laser material is located in the optical cavity preferably a laser material which lases over a range of tunable wavelength is used. A beam expander such as one or more prisms or one or more lenses is provided between the laser material and the diffraction grating. The beam expander increases the cross sectional area of the beam propagating from the laser material prior to its incidenting on the diffraction grating. A pulsed pump laser is provided to excite the laser material in the optical cavity. The pump laser pulses at a rate of about 700 pulses per second (PPS) or more and desirably at about 700 to about 10,000 PPS or greater. Desirably the laser is pumped by the pump laser at a high pump power. Pump power is 4 to 25 watts or higher and preferably 10 watts or greater.
In operation the energy from the pulsed pump laser is directed across the laser material to excite the laser material. The beam from the laser material is directed to a beam expander where the cross sectional area of the beam is expanded at least about 6 times preferably about 6 to about 60 times and desirably 10 times to 60 times or more optionally to about 10 times to about 40 times and desirably at least about 10 times. The expanded beam is then directed to a diffraction grating where the beam is diffracted into multiple beams of differing wavelength. The band widths of the diffracted beam are preselected at a desirable narrow range preferably 0.005 to 0.2 cm
−1
band width desirably 0.01 to 0.1 cm
−1
. A portion of the resulting preselected wavelength beam is removed from the cavity as the laser output.
It is an object of the invention to provide an efficient pulsed solid state laser having a narrow band width beam which is operable at a high repetition rate.
It is an other object of the invention to provide a pulsed solid state laser operable at a high repetition rate having an improved conversion efficiency and high average power output.
It is a further object of the invention to provide a pulsed solid state laser operable at a high repetition rate.
It is a further object of the invention to provide a tunable pulsed solid state laser that is operable at a high repetition rate and has a high conversion efficiency and high average power output.
It is a further object of the invention to provide a tunable pulsed laser that is operable at a high pump power and high conversion efficiency.
It is a further object of the invention to provide a method for operating a tunable pulsed laser at a high repetition rate and high pump power to provide a narrow band width pulse of a preselected frequency while achieving a high conversion efficiency.
Other and further objects will become apparent from the specifications, drawings and claims.
The preferred embodiment of the present invention is illustrated in the drawings and examples. However, it should be expressly, understood that the present invention should not be limited solely to the illustrative embodiment.


REFERENCES:
patent: 4327337 (1982-04-01), Liu
patent: 5121398 (1992-06-01), Rao
patent: 5438416 (1995-08-01), Nater

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