# US 2008/0304534 A1 · Power scaleable thin disk lasers

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- Number: US 2008/0304534 A1
- Document ID: US20080304534A1
- Status: Published application
- Kind: A1
- Application number: 11/760,470
- Filed: 2007-06-08
- Published: 2008-12-11
- Earliest claimed: 2007-06-08
- Assignees: The Boeing Company
- Inventors: David S. Sumida; Hans W. Bruesselbach
- Web page: https://patentgrep.com/patent/US20080304534A1

## CPC

- H01S 3/0604: {in the form of a plate or disc}
- H01S 3/0602: {Crystal lasers or glass lasers (H01S3/063 takes precedence)}
- H01S 3/0612: {Non-homogeneous structure (H01S3/07 takes precedence)}
- H01S 3/025: {of solid state lasers, e.g. housings or mountings}
- H01S 3/0407: {Liquid cooling, e.g. by water}
- H01S 3/0615: {Shape of end-face}
- H01S 3/0621: {Coatings on the end-faces, e.g. input/output surfaces of the laser light}
- H01S 3/0623: {Antireflective [AR]}
- H01S 2301/02: ASE (amplified spontaneous emission), noise; Reduction thereof
- H01S: DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL

## Abstract

A thin disk laser includes a thin disk of a host material incorporating a laser gain medium. The disk has opposite first and second surfaces, at least one of which is non-planar. The first surface is coated with a high reflectivity coating. The second surface has an anti-reflection coating thereon. The shape and mounting of the laser is such that mismatch of the coefficients of thermal expansion between the disk laser and the mount does not affect scaling of the laser to larger size disks for higher power lasers

## Claims

### Claim 1

A laser, comprising:
a thin disk of host material doped with a laser gain medium and having opposite first and second surfaces, wherein at least one of the two surfaces is non-planar;
the first surface having a planar, a concave or a convex shape and being coated with a high reflectivity (HR) coating; and,
the second surface having an anti-reflection (AR) coating thereon.

### Claim 2 (depends on 1)

The laser of claim 1, wherein the second surface has a planar, a concave or a convex shape.

### Claim 3 (depends on 1)

The laser of claim 1, wherein each of the HR coating and the AR coating are adapted to function at both a pump radiation wavelength and the disk laser radiation wavelength.

### Claim 4 (depends on 1)

The laser of claim 1, further comprising apparatus operable to illuminate the second surface with a pump beam of light radiation.

### Claim 5 (depends on 1)

The laser of claim 1, wherein the host material disk is lightly doped with the laser gain medium.

### Claim 6 (depends on 1)

The laser of claim 1, wherein the disk comprises a portion adjacent to the first surface that is heavily doped with the laser gain material, and a portion adjacent to the second surface that comprises un-doped host material.

### Claim 7 (depends on 1)

The laser of claim 1, wherein the laser gain material is selected from the group consisting of ytterbium (Yb), neodymium (Nd), thulium (Tm), holmium (Ho), and chromium (Cr).

### Claim 8 (depends on 6)

The laser of claim 6, wherein the disk comprises a disk of un-doped host material diffusion bonded to a disk of heavily doped host material.

### Claim 9 (depends on 1)

The laser of claim 1, wherein the disk is circular or elliptical.

### Claim 10 (depends on 6)

The laser of claim 6, wherein the first surface is convex and the heavily doped host material portion extends laterally to a portion of the first surface that is less than the entire first surface.

### Claim 11 (depends on 9)

The laser of claim 9, wherein the convex shape of the disk first surface and the HR coating are operable to deflect amplified spontaneous emission and to suppress transverse parasitic oscillations in the thin disk of the laser.

### Claim 12 (depends on 1)

The laser of claim 1, wherein the host material is yttrium aluminum garnet (YAG) and the crystallographic orientation of the YAG disk laser is <110> in a direction parallel to the lasing axis of the disk laser.

### Claim 13 (depends on 1)

The laser of claim 1, wherein at least one of the first and second surfaces is figured radially by polishing away from a selected nominal curvature a volume of the host material of about one micron deep or less over one or more radial increments of about one millimeter, as measured from the center of the disk.

### Claim 14 (depends on 13)

The laser of claim 13, wherein the figuring compensates for optical path distortion.

### Claim 15 (depends on 14)

The laser of claim 14, wherein the optical phase distortion is caused by radial thermal gradients.

### Claim 16 (depends on 1)

The laser of claim 1, wherein the host material has at least one of a higher thermal conductivity, a higher absorption cross section, a broader absorption, or a reduced quenching effect, than doped yttrium aluminum garnet (YAG).

### Claim 17 (depends on 16)

The laser of claim 16, wherein the host material is selected from the group consisting of Lu2O3, YVO4, LuVO4, Sc2O3, LaSc3(BO3)4, KGd(WO4)2, and KY(WO4)2.

### Claim 18 (depends on 1)

The laser of claim 1, further comprising:
a planar first surface spaced apart from the second surface;
a vertical sidewall connecting the first and second surfaces; and
a border on the outer surface of the vertical wall.

### Claim 19 (depends on 18)

The laser of claim 18, wherein the border comprises a light scattering surface of the vertical wall.

### Claim 20 (depends on 18)

The laser of claim 18, wherein the border comprises a material clad to the vertical wall that is absorbing at the wavelength of the laser light emitted by the laser.

### Claim 21

A laser assembly, comprising:
a thin disk laser having opposite first and second surfaces, wherein at least one of the surfaces is non-planar, the first surface having a planar, concave or convex shape and a high reflectivity (HR) coating thereon, the second surface having a flat, a concave or a convex shape with an antireflection (AR) coating thereon;
a laser housing having a hollow interior for circulating a coolant fluid over the first surface and for receiving and supporting the thin disk laser at a peripheral edge thereof such that the first surface faces toward the hollow interior of the housing, the housing further including a seal formed at the peripheral edge of the laser disk so as to sealingly retain both the laser disk and the coolant fluid therein; and,
apparatus for illuminating the second surface with a pump beam of light to excite the thin disk laser.

### Claim 22 (depends on 21)

The laser assembly of claim 21, wherein the coolant is recirculated between the housing and an external chiller for conveying heat away from the disk laser.

### Claim 23 (depends on 22)

The laser assembly of claim 22, wherein the coolant fluid is maintained at a temperature of about 100 degrees K or lower.

### Claim 24 (depends on 21)

The laser assembly of claim 21, wherein the HR coating on the first surface comprises a first mirror of a resonant cavity, and further comprising:
a second mirror disposed external to the laser disk and facing the AR coated second surface of the laser disk, the second mirror comprising a second mirror of the resonant cavity, wherein the second mirror is operable to reflect a first portion of the laser light emitted by the thin disk laser back through the thin disk laser second surface and to couple out a second portion of the laser light in the form of an output beam.

### Claim 25 (depends on 24)

The laser assembly of claim 24, wherein the pump beam has an intensity profile that is continuous and that monotonically decreases in a radial direction from a maximum at the disk laser center to a substantially negligible intensity at a selected radial distance from the laser disk center.

### Claim 26 (depends on 25)

The laser assembly of claim 25, wherein the selected radial distance is less than the radius of the disk laser.

### Claim 27 (depends on 26)

The laser assembly of claim 26, wherein the laser has a mode intensity profile at the second surface of the thin-disk laser that is determined by at least one of the curvature of the first surface, the curvature of the second surface, a figure correction of at least one of the first and second surfaces, the position of the second mirror, and the radius of curvature of the second mirror.

### Claim 28 (depends on 27)

The laser assembly of claim 27, wherein the pump light intensity profile is equal to or less than the laser mode profile.

### Claim 29 (depends on 1)

A method of lasing, the method comprising:
providing a laser in accordance with claim 1; and,
irradiating the second surface of the laser with a beam of light from a pump source.

### Claim 30 (depends on 29)

The method of claim 29, further comprising:
positioning an output mirror facing and spaced apart from the laser and having a partial transparency at the lasing wavelength of the laser so as to form a laser resonator cavity in combination with the HR coating on the second surface of the laser.

### Claim 31 (depends on 29)

The method of claim 29, further comprising:
mounting the laser in a housing adapted to circulate coolant in direct contact with the second surface of the laser; and,
circulating a cooling fluid over the second surface of the laser during operation thereof.

### Claim 32 (depends on 29)

The method of claim 29, further comprising figuring the laser by polishing away from a selected nominal curvature a volume of host material from either or both sides of the laser about one micron deep or less over one or more radial increments of about one millimeter, as measured from the center of the disk.

### Claim 33 (depends on 29)

The method of claim 29, further comprising shaping the beam of the pump laser to have an intensity profile that is continuous and that monotonically decreases in a radial direction from a maximum at the disk laser center to a substantially negligible intensity at a selected radial distance from the laser disk center.

### Claim 34 (depends on 29)

The method of claim 29, wherein the disk includes a vertical peripheral sidewall, and further comprising:
forming a light scattering or absorbing border on the vertical sidewall.