US-12627113-B2 - Optical amplifier

US12627113B2US 12627113 B2US12627113 B2US 12627113B2US-12627113-B2

Abstract

An optical amplifier comprises a gain medium having an input surface and an output surface wherein the output surface is larger than the input surface. The gain medium may be frustum shaped. The optical amplifier includes a negative diverging lens to receive an extraction laser beam and to cause the laser beam to expand as the beam passes through the gain medium. The amplifier further comprises a positive collimating lens configured to receive the expanding amplified beam and reduce the divergence. The gain medium can be pumped by counter-propagating radiation. The fluence of the laser beam within the gain medium is configured to be near constant along the length of the gain medium and may be within 1.5-2.0 F SAT . The gain medium may be doped with dopant to provide gain, with larger concentration of dopants proximal the input surface and smaller concentration proximal the output surface.

Inventors

Stephen Anthony Payne
Raymond Beach
Jean-Michel DI NICOLA
Alvin Erlandson
John Heebner
Jeremy Lusk
William A. Molander
Samuel Edward Schrauth
Jen Nan Wong

Assignees

LAWRENCE LIVERMORE NATIONAL SECURITY, LLC

Dates

Publication Date: 20260512
Application Date: 20220304

Claims (20)

1 . An optical amplifier comprising: first optics configured to receive a laser beam and output an expanding beam; a gain medium comprising material configured to provide optical gain to laser light transmitted therethrough, said gain medium having an input surface and an output surface separated from each other in a longitudinal direction by a length, said input surface extending in first and second directions orthogonal to said longitudinal direction so as to have an input area, said output surface extending in said first and second directions orthogonal to said longitudinal direction so as to have an output area, said output area being larger in both said first and second directions than said input area, said gain medium being positioned such that said expanding beam is received into said input surface and output through said output surface, said expanding beam having a larger beam size in both said first and second directions at said output surface than at said input surface; an optical pump source configured to provide output pump radiation to said gain medium such that said material provides optical gain to said expanding beam transmitted therethrough, and second optics positioned to receive the laser beam output from the gain medium and to reduce the divergence of said laser beam.
2 . The optical amplifier of claim 1 , wherein said gain medium comprises a frustum of said material configured to provide optical gain.
3 . The optical amplifier of claim 1 , wherein said gain medium does not comprise a waveguide.
4 . The optical amplifier of claim 1 , wherein said input surface, said output surface, or both are curved.
5 . The optical amplifier of claim 1 , wherein said material does not comprise an electrically-energized semiconductor.
6 . The optical amplifier of claim 1 , wherein said gain medium has a larger small-signal gain at said input surface than at said output surface.
7 . The optical amplifier of claim 1 , wherein said gain medium is doped with dopants so as to provide a higher average dopant level closer to said input surface than said output surface.
8 . The optical amplifier of claim 1 , wherein said gain medium is doped with dopants so as to provide on average a gradient in dopant level from said input surface to said output surface.
9 . The optical amplifier of claim 1 , wherein said laser beam in the gain medium has a constant fluence to within about ±50% along the longitudinal direction thereof.
10 . The optical amplifier of claim 1 , wherein said laser beam in the gain medium has a fluence within of about 1 to 2 times F sat or within ±50% thereof along the longitudinal direction thereof.
11 . The optical amplifier of claim 1 , wherein said first optics comprises a negative lens.
12 . The optical amplifier of claim 1 , wherein said second optics comprises a positive lens.
13 . The optical amplifier of claim 1 , wherein said second optics comprises a hyperbolic lens.
14 . The optical amplifier of claim 1 , wherein said pump radiation is introduced to said gain medium through said second optics.
15 . The optical amplifier of claim 1 , further comprising a dichroic reflector disposed in an optical path between said pump source and said gain medium such that said pump radiation is directed through said dichroic reflector to said gain medium and an amplified laser beam is reflected from said dichroic reflector toward an output of said optical amplifier.
16 . The optical amplifier of claim 1 , wherein said expanding laser beam and said pump radiation are counter-propagating through said gain medium.
17 . The optical amplifier of claim 1 , wherein said optical amplifier includes ASE-absorbing edge cladding.
18 . The optical amplifier of claim 1 , wherein said first optics has an f-number in a range from at least 1.5 to 10.
19 . An optical amplifier comprising: a gain medium comprising material configured to provide optical gain to laser light transmitted therethrough, said gain medium having an input surface and an output surface separated from each other in a longitudinal direction by a length, said input surface extending in first and second directions orthogonal to said longitudinal direction so as to have an input area, said output surface extending in said first and second directions orthogonal to said longitudinal direction so as to have an output area, said output area being larger in both said first and second directions than said input area, wherein said gain medium comprises a non-gaseous medium, and wherein said gain medium has a larger small-signal gain at said input surface than at said output surface.
20 . The optical amplifier of claim 19 , wherein the gain medium comprises a dielectric crystal comprising garnet, strontium fluoride, lithium fluoride, yttrium aluminum garnet (YAG), or yttrium lithium fluoride (YLF) or that the gain medium comprises ceramic.

Description

FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT This invention was made with Government support under Contract No. DE-AC52-07NA27344 awarded by the United States Department of Energy. The Government has certain rights in the invention. BACKGROUND Field The present disclosure relates generally to optical amplifiers, gain media and extraction of stored energy from gain media, and more specifically to gain media configured to accommodate an expanding laser beam as well as systems and methods related thereto. Description of the Related Art A laser beam 10 from as laser 12 can be amplified by transmitting the laser beam through a gain medium 14 to produce an amplified laser beam 16 such as shown in FIG. 1, which depicts an optical amplifier 5 for amplifying a laser beam. Pump radiation 18 from a pump source 20 may be used to energize the gain medium 14, which can store large amounts of energy that is extracted by the laser beam 10 as the laser beam propagates through the gain medium. Designs and methods for efficient extraction of energy from the gain medium 14 can be desirable. SUMMARY The present disclosure relates generally to methods and apparatus for more efficiently extracting optical energy from a gain medium and imparting such optical energy into a laser beam propagating through the gain medium. Various devices, systems, and methods described herein utilize a gain medium having lateral dimensions as well as a transverse gain profile that increase along the length of the gain medium. Such a gain medium may, for example, comprise a material configured to provide optical gain having the shape of a frustum with an input surface or face and an output surface or face wherein the output is larger in area than the input. For example, in one design, an optical amplifier comprises a first lens configured to receive a laser beam and output an expanding beam and a gain medium comprising material configured to provide optical gain to laser light transmitted therethrough. The gain medium has an input surface and an output surface separated from each other in a longitudinal direction. The input surface extends in first and second directions orthogonal to the longitudinal direction so as to have an input area. The output surface also extends in the first and second directions orthogonal to the longitudinal direction so as to have an output area. The output area of the output surface of the gain medium is larger in both the first and second directions than the input area. The gain medium is positioned to receive the expanding beam of light into said input surface and to output said expanding beam through said output surface. The expanding beam also has a larger beam size in both the first and second directions at the output surface than at the input surface. The optical amplifier further comprises an optical pump source configured to provide output pump radiation to the gain medium such that the optical material provides optical gain to the expanding beam transmitted therethrough. Also disclosed herein is an optical amplifier comprising a gain medium comprising material configured to provide optical gain to laser light transmitted therethrough. The gain medium has an input surface and an output surface separated from each other in a longitudinal direction. The input surface extends in first and second directions orthogonal to the longitudinal direction so as to have an input area. The output surface also extends in the first and second directions orthogonal to the longitudinal direction so as to have an output area. The output area is larger in both the first and second directions than the input area. The present disclosure may be used in amplification systems and high power laser systems possibly to provide system performance advantages. BRIEF DESCRIPTION OF THE DRAWINGS The drawings described herein are for illustrative purposes only of selected embodiments and not all possible implementations and are not intended to limit the scope of the present disclosure. Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings. FIG. 1 is a schematic view of an example optical amplifier for amplifying a laser beam. FIG. 2 is a schematic view of an example optical amplifier comprising a gain medium that transmits a laser beam therethrough that is to be amplified. A negative lens causes the laser beam to expand or diverge as the laser beam propagates through the gain medium disposed downstream of the negative lens. The gain medium and a transverse gain profile therein increases in cross-sectional area with distance along the length thereof in conjunction with the expansion or divergence of the laser beam. In the design shown, the gain medium is optically pumped by a pump beam that is counter-propagating with respect to the laser beam that is being amplified. FIG. 3A shows a plot on axes of beam width (in cm) and length (in cm) that depicts the increasing beam width of an expanding beam in