Optical: systems and elements – Optical frequency converter – Harmonic generator
Reexamination Certificate
2002-02-13
2004-08-10
Lee, John D. (Department: 2874)
Optical: systems and elements
Optical frequency converter
Harmonic generator
C359S330000
Reexamination Certificate
active
06775053
ABSTRACT:
BACKGROUND
1. Field of Endeavor
The present invention relates to preamplification and more particularly to preamplification based on optical parametric amplification.
2. State of Technology
The article, “Evaluation of an Ultrabroadband High-gain Amplification Technique for Chirped Pulse Amplification Facilities” by John Collier, Cristina Hernandez-Gomez, Ian N. Ross, Pavel Matousek, Colin N. Danson, and John Walczak in
Applied Optics-LP
, Volume 38, Issue 36, 7486-7493, December 1999, provides the following information, “Recently, an amplification technique for ultrashort pulses was explored in detail in a theoretical paper by Ross, et al. Opt. Commun. 144, 125 (1997). The technique, based on nonlinear optics, is called optical parametric chirped pulse amplification. It has a number of features that, in principle, make it highly attractive. It primarily offers extremely large gains simultaneously with extremely large bandwidths. Additional attractions are virtually no spatial and temporal phase distortion of the amplified pulse, high efficiencies and a low thermal loading, reduced amplified spontaneous emission levels, small optical material lengths, and an inherent simplicity of implementation. We present an evaluation of the technique as a front-end amplifier for the ultrashort pulse amplification chain of the Vulcan laser system. Such a device could replace some of the existing amplification in Nd:glass and additionally have a wider effect as a direct replacement of Ti:sapphire regenerative amplifiers on large-scale chirped pulse amplification scale facilities.”
U. S. Pat. No. 5,047,668 for optical walkoff compensation in critically phase-matched three-wave frequency conversion systems to Walter R. Bosenberg patented Sep. 10, 1991 describes a walkoff-compensated frequency conversion system such as an optical parametric oscillator includes a pair of nonlinear crystals, such as Beta-Barium Metaborate, aligned in an optical cavity with their optical axes at an angle .THETA. with respect to the axis of the cavity. The crystals are oppositely disposed with respect to the cavity axis so that the angle between their respective optical axes is 2.THETA. In an optical parametric oscillator, the crystals are pumped to produce optical parametric luminescence and frequency conversion, the luminescence being emitted as signal and idler beams. The opposite arrangement of the optical axes of the crystals causes the pumping beam to walk off the signal beam in the first crystal and to walk on the signal beam in the second crystal. Similar walkoff compensation is provided in other frequency conversion systems wherein crystal pairs are oppositely disposed along a cavity optical axis.
U.S. Pat. No. 6,181,463 for quasi-phase-matched parametric chirped pulse amplification systems by Almantas Galvanauskas, et al.; patented Jan. 30, 2001 provides the following information, “Ultrashort pulse lasers and amplifiers belong to a particular class of laser devices which generate ultimately short optical pulses (at the optical-wavelength limit) with durations in the femtosecond (10.sup.-15 s) to picosecond (10.sup.-12 s) regimes. Potential use of such pulses is determined by their characteristic features, which include short duration, high peak power and high spatial and temporal coherence. Diode lasers are compact sources of laser emission which possess two unique technological advantages. First, diode lasers provide direct conversion from electrical to optical power with high efficiency. Second, they are monolithic devices with small dimensions (typically less than 1 mm). Consequently, their parameters such as size, robustness, reliability, life-time, manufacturability and cost are substantially better than corresponding parameters of other laser structures, such as gas, dye or bulk solid-state lasers. These key features make them ideally suitable for developing commercially viable laser sources. However, direct use of diode lasers in the generation of high-energy ultrashort pulses is limited. Essentially this is determined by the small cross-sectional area of a single-mode diode. Catastrophic damage to the diode and severe nonlinear distortions of the ultrashort pulses restricts obtainable peak intensities. Additionally, due to the same small cross-sectional area, stored energy and saturation fluency are also limited. Maximum energies directly obtainable from a laser diode are limited to about 100 pJ, which is at the low limit of practically significant ultrashort pulse energies. While the effective cross-sectional area of a laser diode can be increased by resorting to multiple-transversal-mode structures or multiple-stripe structures, the requirement of spatial and temporal coherence does not permit direct generation of ultrashort pulses with such devices.
This necessitates using diodes as pump sources for other classes of ultrashort-pulse lasers and amplifiers in order to develop practical systems. Rare-earth doped fiber lasers represent one such class of devices and are closest to semiconductor gain media in compactness, as mainly determined by the small transverse dimensions of the fiber. The typical diameter of a fiber structure is less than 1 mm. Unlike a semiconductor laser, a fiber laser can have a length of several meters, but due to the small transverse dimensions it can be spooled to occupy a small space. In effect, the fiber laser is a one dimensional structure, with the transverse distribution of the optical field being the same at any longitudinal position. Rare-earth doped fibers can be diode-laser pumped. For example, known Er-doped fiber laser systems have been pumped with existing high-power laser diodes emitting at 1480 nm or 980 nm.
As reported in Broad-area Diode-pumped 1 W Femtosecond Fiber System, A. Galvanauskas, M. E. Fermann, D. Harter, J. D. Minelly, G. G. Vienne, J. E. Caplen, Conference on Lasers and Electro-Optics, vol. 9 1996 OSA Technical Digest Series (Optical Society of America, Washington, D.C., 1996) pp. 495, hereby incorporated herein by reference, high power multimode diode pump light is efficiently converted into a high power ultrashort pulse output by fiber cladding-pumping techniques and chirped pulse amplification. In general, chirped pulse amplification is necessary for any quantum amplifier in order to extract the maximum available energies without incurring nonlinear distortion of the ultrashort pulses or optical damage to optical components or the gain medium. Typically, the peak intensity of an ultrashort pulse, with an energy equal to the saturation energy, is higher than the saturation fluency of the medium. However, in order to preserve spatial and temporal coherence and to sustain ultrashort pulses, the fiber output has to be single-mode. This puts constraints on the fiber core size and, consequently, on the maximum obtainable pulse energies and peak intensities, for reasons here equivalent to the case of a single-mode semiconductor laser. Maximum obtainable energies for a single-mode fiber, however, are substantially higher than for a semiconductor. The maximum, saturation-fluency-limited energies have already been experimentally produced with some diode pumped Er-fiber chirped pulse amplification systems, yielding pulse energies of more than 10 .mu.j after amplification and recompression. However, for a variety of practical applications, such as micromachining, optical surgery, etc. much higher ultrashort pulse energies are required (typically in the range of 1 to 10 mj).
To obtain these pulse energies, bulk quantum amplifiers have been conventionally used. In a bulk medium, the beam size is substantially larger than the single-mode guided beam in a fiber or a semiconductor structure, alleviating the problem of high peak intensities. Furthermore, certain solid-state gain media have properties which permit design of compact devices. However, a number of limitations, as determined by the general properties of quantum amplifiers, make it practically difficult to implement compact solid-state designs for direct amplification of ultrashort high-energy pu
Bonner Randal A.
Jovanovic Igor
Lee John D.
Scott Eddie E.
The Regents of the University of California
Thompson Alan H.
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