Solid state laser

Details Solid state laser Solid state laser

2001-08-20

2003-12-30

Ip, Paul (Department: 2828)

Coherent light generators

Particular resonant cavity

C345S030000

Reexamination Certificate

active

06671305

ABSTRACT:

FIELD OF THE INVENTION
The invention relates to a compact optically side-pumped solid-state laser, and more particularly to a laser that can simultaneously emit laser beams at different wavelengths. The invention also relates to a compact three color (RGB) laser architecture suitable for color projection display applications.
BACK GROUND OF THE INVENTION
Red, green and blue (RGB) lasers offer demonstrable benefits over incandescent light sources for high-performance imaging applications. Greater color saturation, contrast, sharpness, and color-gamut are among the most compelling attributes distinguishing laser displays from conventional imaging systems employing arc lamps. Any desired color within the CIE or NTSC color space can be obtained by appropriately mixing the primary colors R, G, and B. An ideal laser light source for projection display applications should provide multi-watt R, G, and B outputs, either cw or Q-switched at high repetition rates for frequency mixing.
A RGB laser light source display system has been disclosed, for example, in commonly assigned U.S. patent application Ser. No. 09/319,058, which is incorporated herein by reference. As disclosed in the reference, a Nd:YVO
4
MOPA laser source emits fundamental laser radiation at 1.064 &mgr;m, which is frequency-doubled to produce green, whereas red and blue are produced R, G and B are generated by sum-frequency generation (SFG) and/or frequency-doubling using radiation produced by an OPA and Ti:sapphire laser pumped at the 1.064 &mgr;m fundamental wavelength. Nd:YVO
4
is a laser material with a low lasing threshold and a high slope efficiency, a large stimulated emission cross-section, and a high coefficient of absorption over a wide pumping wavelength bandwidth of 802 to 820 nm. The high absorption of pump radiation makes Nd:YVO
4
suitable for side-pumping with diode lasers instead of end pumping.
In a side-pumped configuration, the direction of pumping is transverse or orthogonal to the longitudinal axis of the laser cavity. Considerable care must be taken to ensure that there is a high degree of overlap between the laser mode and the pumped volume. The absorption depth of the pump light depends on the concentration of Nd-atoms in the crystal, so that the conversion efficiency of the laser can be optimized by using a low absorption material with a large mode volume. The absorption coefficient can be controlled by adjusting the concentration of Nd-atoms in Nd:YVO
4
.
Nd
3+
-ions can lase not only at the
4
F
{fraction (3/2)}
→
4
I
{fraction (11/2)}
(1.064 &mgr;m) transition, but also, albeit somewhat less efficiently, at the
4
F
{fraction (3/2)}
→
4
I
{fraction (13/2)}
(1.342 &mgr;m) transition. One of these transitions can be favored over the other by a suitable cavity design. Blue emission can be generated from the 1.342 &mgr;m fundamental by second harmonic generation (SHG) of 670 nm radiation which is then combined (SFG) with the 1.342 &mgr;m residual to produce 447 nm blue emission. Green emission at 532 nm can be produced from the 1.064 &mgr;m fundamental by SHG. Red emission at 628 nm can be produced from the 1.064 &mgr;m fundamental by first shifting 1.064 &mgr;m to 1.54 &mgr;m using an OPO, followed by SHG.
It would therefore be desirable to provide an efficient side-pumped solid state laser configuration with a high degree of spatial overlap between the region of highest gain and the laser mode. It would also be desirable to provide a compact laser configuration emitting at two different wavelengths that can be used for efficiently generating the three primary colors R, G and B, for example, by nonlinear optical processes.
SUMMARY OF THE INVENTION
The invention is directed to a compact solid-state laser with an optimized spatial overlap between the mode of the laser beam propagating in the laser material and the pump beam.
According to aspect of the invention, a slab-type solid-state laser oscillating device includes a slab-type laser medium for generating at least two laser beams which traverse the laser medium between two end faces in a longitudinal direction. The laser medium is optically transversely pumped. At least one of the end faces has Brewster surfaces which are cut at an angle with respect to the longitudinal direction, intersect along a line, wherein the angle is equal to a Brewster angle of the laser medium for the laser beams. A partially reflecting mirror and a high-reflectivity mirror form an optical cavity. Each of the laser beams passes through a different Brewster surface and the laser beams are simultaneously optically pumped.
Embodiments of the invention may include one or more of the following features. At least one high-reflectivity mirror can be obliquely disposed and offset from a longitudinal center axis of the slab-type laser medium. The laser beams passing through the Brewster surface can have the same or a different lasing wavelength. A fold prism can be disposed at the end of the slab-type laser medium opposite the Brewster surfaces, wherein the fold prism retro-reflects the laser beam passing through one of the Brewster surfaces to subsequently pass through another Brewster surface. The laser medium may be Nd:YVO
4
or Nd:YAG with lasing wavelengths of approximately 1.06 &mgr;m and 1.34 &mgr;m.
According to another aspect of the invention, a compact multi-wavelength solid state laser has a solid state laser element made of a material capable of lasing at at least two wavelengths. The solid state laser defines a center line and has opposing side faces extending substantially parallel to the center line, with pump radiation coupled to the side faces. The solid state laser element further includes end faces, with at least one of the end faces comprising a Brewster dispersing prism with twin exit faces formed on opposite sides of the center line of the solid state laser element. Two laser cavities are formed on opposite sides of the center line, with a first cavity including a first mirror having a high reflectivity at a first of the at least two wavelengths, a first output mirror, and a first portion of the solid state laser element with one of the twin faces of the Brewster dispersing prism, and the second cavity including a second mirror having a high reflectivity at a second of the at least two wavelengths, a second output mirror, and a second portion of the solid state laser element with the other twin face of the Brewster dispersing prism.
Embodiments of the invention may include one or more of the following additional features. At least one modulator, for example, a Q-switch, may disposed in one or several of the laser cavities. The Brewster dispersion prism can be formed integrally with or as a separate element from the solid state laser element. If the Brewster dispersion prism is formed as a separate element, a quarter-wave plate can be interposed between the Brewster dispersion prism and the end face of the solid state laser element. The Brewster dispersion prism can be formed of glass or another material transparent at the wavelengths produced by the solid state laser element.
The laser output beams having at least one of the lasing wavelengths of approximately 1.06 &mgr;m and 1.34 &mgr;m can be converted to RGB output beams useful, for example, in color projection display applications by employing at least one of an optical parametric oscillator, second harmonic generator and sum frequency mixer.
According to still another aspect of the invention, a compact side-pumped solid state laser includes a solid state laser element that defines a longitudinal center line and has opposing side faces extending substantially parallel to the center line, with pump radiation coupled to the side faces. The solid state laser element further includes end faces, with one of the end faces comprising a Brewster dispersing prism with twin exit faces formed on opposite sides of the center line of the solid state laser element, and with the other end face comprising a 180° fold prism. A laser cavity includes a high-reflectivity mirror obliquely disposed and o

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