University of Michigan

United States of America as Represented by the Secretary of the Air Force

Hughes Aircraft Company

Stephen C Rand

Joseph A Wysocki

William M Fisher

Richard M Laine

Ricardo C Pastor

Raj Rao Nadakuditi

Eric Michielssen

Thomas Hinklin

Robert A Cronkite

Curtis Jin

Ping Xie

Larry G DeShazer

Guy R Williams

Schemes are described to produce quasi-static charge separation, Terahertz radiation, and programmable magnetic field generation using linearly-polarized light in unbiased, transparent insulators. The methods exploit a recently-observed magneto-electric optical nonlinearity that produces intense magnetization in undoped, homogeneous dielectrics. Analysis reveals that strong magnetic effects can be induced at modest optical intensities even with incoherent light. Consequently, efficient solar power conversion is feasible without the semiconductor processing or electron-hole pair generation that is required in conventional photovoltaic cells. Additionally, conditions and techniques are described to generate intense THz radiation in unbiased substrates and large magnetic fields orientated transverse to the direction of propagation of light, without the need for any external permanent magnetic or electromagnetic apparatus.

Optically-induced charge separation and induced magnetism in dielectrics for optical energy conversion and intense magnetic field generation

The method, system, and computer-readable medium increase transmission of waves through a highly scattering random medium. Transmission is increased by iteratively refining wavefronts using measurements of the backscatter wavefronts resulting from transmission of waves into the medium. The process of double phase conjugation by time-reversing a wavefront, transmitting the time-reversed wavefront into the medium, and time-reversing the reversing backscatter wavefront is leveraged to implement the method in a physical system using a phase conjugate mirror. In an embodiment, transmission may be increased by phase-only modulation of the wavefronts. In an embodiment, the invention may be used to focus transmission through the medium to a location opposite the wave source.

Methods for increasing transmission through scattering random media

Doped, nanosize metal oxide particles have been shown to exhibit stimulated emission and continuous-wave laser action when energized appropriately, for example by electron beams. The doped particles are useful as solid state lasing devices and &ldquo;laser paints&rdquo;. Particles containing homogeneously distributed dopant atoms in concentrations greater than the thermodynamic solubility in the metal oxide matrix, and having in some circumstances, unusual oxidation states, have been produced.

Ultrafine powders and their use as lasing media

Four-fold and higher order lasers pumped by multiphoton absorption, avalanche mechanisms, or other means of internal upconversion for continuous-wave and continuous-wave mode-locked lasers. A solid-state laser system is contained within an astigmatically compensated cavity containing first and second mirrors. The gain medium is formed of a crystal of lithium yttrium fluoride heavily doped (5%) with trivalent erbium, or another form of crystal, such as CaF.sub.2 where the dopant atoms are clustered in quartets. The crystal, in a lithium yttrium fluoride embodiment, is approximately 3 mm thick with both sides thereof being polished flat to a laser grade finish. A pumping source supplies a pumping energy having a wavelength of 1.5 .mu.m to the gain medium, which wavelength is considerable longer than the output wavelength (701.5 nm) of the laser system. The gain medium may additionally be an alkali vapor formed of Cesium or Rubidium.

Four-fold and higher order continuous-wave upconversion lasers

A laser source which operated under the principals of cooperative unconversion produces controllable optical pulses at wavelengths which are shorter than the wavelength of the laser energy which pumps the gain medium. The source is a solid-state laser which employs a five percent Er:LiYF.sub.4 crystal which is arranged in an astigmatically-compensated 3-mirror cavity. Pumping is achieved at 1.5 microns in the infrared, and the system operates in a continuous-wave, mode-locked fashion in the green spectral region at approximately 544 nm. The cooperative inversion mechanism involves energy pooling by trios of excited rare earth dopant ions in the laser medium. Q-switching is achieved with the use of intracavity amplitude modulation so as to achieve three-fold upconversion. A 3-mirror astigmatically-compensated cavity with the gain medium permits modulation of losses in a manner which cannot be achieved with known systems and achieves high stability.

Mode-locked upconversion laser source

Continuous laser action is sustained by a new pumping mechanism which relies exclusively on cooperative electronic transitions of coupled atoms or ions in solids. The present invention is the first of a new class of laser device which depends on energy-sharing interactions between colliding atoms in gases or active dopants in solid laser media to create the population inversion needed for amplification of light. In one specific embodiment, a laser crystal which is formed of calcium fluoride is doped heavily with trivalent erbium, and is provided with reflective coatings on respective first and second surfaces. A pumping energy is supplied whereby a pair of atoms are elevated to an initial excited state. Subsequently, one of the atoms loses energy so as to assume a ground state, the energy released thereby being made available to excite the second atom to a still higher quantum energy state. Thus, a cooperative energy interaction between the pair of atoms results in the double excitation of one of the atoms above the initial excitation state. The excited ion subsequently, upon relaxation to its initial excited energy level, causes the issuance of the laser photon. The invention is not limited to solid laser media, and may be employed in gas or liquid laser systems. Additionally, transition metal ions may be employed as an alternative to rare earth ions.

Continuous-wave pair-pumped laser system

Continuous laser action is sustained by a new pumping mechanism which relies exclusively on cooperative electronic transitions of coupled atoms or ions in solids. The laser depends on energy-sharing interactions between a trio of atoms in gases or active dopants in solid laser media to create the population inversion needed for amplification of light. In one specific embodiment, the laser crystal is formed of calcium fluoride doped heavily with trivalent erbium, and is provided with reflective coatings on respective first and second surfaces. A pumping energy is supplied whereby a three atoms are elevated to an initial excited state. Subsequently, two of the atoms lose energy so as to assume a ground state, the energy released thereby being made available to excite the third atom to a still higher quantum energy state. Thus, a cooperative energy interaction between the trio of atoms results in the double excitation of one of the atoms above the initial excitation state. The excited ion subsequently, upon relaxation to its initial excited energy level, causes the issuance of the laser photon.

Trio upconversion laser system

An improved polarization preserving birefringent fiber optic member is provided having cross-sectional circular cladding and core members of soft glasses. A metallic coating of an approximately circular configuration, that is offset from the axis of the core and cladding members, is provided with sufficient thickness to provide an anisotropic variation in compressional strain on the core member to create the anisotropy of the refracted index of the core member for preserving polarization characteristics. The optical fiber can be formed by heating a mechanical composite of a core rod and cladding tube, drawing the core and cladding to form a fused fiber and transporting the drawn fiber through a coating bath to provide the variation in thickness.

Polarization preserving optical fiber and method of manufacturing

A nonlinear fiber-optic device including a single mode optical fiber having a longitudinal axis, for transmitting light therethrough of a given wavelength, and having a core and a cladding layer, a portion of the cladding layer being removed until a remaining portion of the cladding layer has a thickness of about one half of the given wavelength or less, and a nonlinear optical crystal having an optical axis, in contact with said remaining portion of the cladding layer, the optical axis of the crystal being substantially perpendicular to the longitudinal axis of the fiber.

Phase-matchable, single-mode fiber-optic device

A nonlinear second order signal processing apparatus having a number of high quality optical fibers that are embedded in a nonlinear optical material in such a way that their cores are in evanescent contact with one another and the nonlinear medium.

Nonlinear optical apparatus using optical fibers

A passive laser Q-switch is fabricated from a crystal which can form saturable color centers, such as lithium fluoride. The arbitrarily long crystal is irradiated with electrons from the side, or radially, to impart a radial distribution of saturable color centers therein, with the highest density at the periphery of the crystal. Optionally, the crystal can also be irradiated axially with electrons or in any direction with another form of radiation having greater penetration into the crystal, such as gamma radiation, to establish a base level of saturable color centers throughout the crystal. The crystal having the radial distribution of color centers acts as a Q-switch, but additionally tends to reduce beam divergence and increase the brightness of the laser beam by virtue of the nonlinear bleaching mechanism.

Solid state laser Q-switch having radial color center distribution

A process of fabricating a hybrid single crystal fiber having nonlinear optical properties such as frequency doubling. Said process includes applying a force to a fiber core resting upon a bulk nonlinear crystal such as LiIO.sub.3 in a saturated solution of LiIO.sub.3 in water. After the core is embedded a sufficient distance into the crystal the force is removed.

Hybrid single crystal optic fibers by embedding

A process of fabricating a hybrid single crystal fiber having nonlinear optical properties such as frequency doubling. Said process includes placing a fiber core upon a bulk nonlinear crystal such as LiIO.sub.3 in a saturated growth solution of LiIO.sub.3 in water. After the core is encased a sufficient distance crystal growth is stopped.

Growing community of inventors

Ann Arbor, MI, United States of America

Stephen C Rand