Coherent light generators – Particular active media
Reexamination Certificate
2002-10-01
2004-09-21
Wong, Don (Department: 2828)
Coherent light generators
Particular active media
C372S070000, C372S053000
Reexamination Certificate
active
06795464
ABSTRACT:
TECHNICAL FIELD
These teachings relate generally to the generation of laser action in scattering media and, more specifically, to the use of random laser action for remote sensing and other applications.
BACKGROUND
Various physical phenomena associated with the multiple scattering of electrons have been known for some time. Over the past several years optical analogs of these phenomena have been observed, as reported by Dalichaouch, R., Armstrong, J. P., Schultz, S., Platzman, P. M. & McCall, S. L. Microwave Localization by 2-Dimensional Random Scattering.
Nature
354, 53 (1991); Sparenberg, A., Rikken, G. & van Tiggelen, B. A. Observation of photonic magnetoresistance.
Physical Review Letters
79, 757 (1997); and Scheffold, F. & Maret, G. Universal conductance fluctuations of light.
Physical Review Letters
81, 5800 (1998).
In addition to these effects, it was predicted in 1968 that multiple scattering of light in the presence of amplification could lead to an instability and laser-like emission, Letokhov, V. S.
Sov. Phys. JETP
26, 835 (1968). Such an experimental situation was realized in a number of physical forms included use of powdered laser crystals: Gouedard, C., Husson, D., Sauteret, C., Auzel, F. & Migus, A. Generation of Spatially Incoherent Short Pulses in Laser-Pumped Neodymium Stoichiometric Crystals and Powders.
Journal of the Optical Society of America B
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Optical Physics
10, 2358 (1993), Wiersma, D. S. & Lagendijk, A. Light diffusion with gain and random lasers.
Physical Review E
54, 4256 (1996), and high gain laser dyes in combination with various scattering media: Lawandy, N. M., Balachandran, R. M., Gomes, A. S. L. & Sauvain, E. Laser Action in Strongly Scattering Media (Vol 368, Pg 436, 1994).
Nature
369, 340 (1994). Most recently, experiments using zinc-oxide powders have provided evidence for random laser action in the presence of Anderson localization: Cao, H. et al. Random laser action in semiconductor powder.
Physical Review Letters
82, 2278 (1999). Considerable experimental work on the physical mechanisms and possible uses of the random laser action followed the discovery of the dye based system. Examples of research into this area are found in the following articles: Balachandran, R. M., Perkins, A. E. & Lawandy, N. M. Injection Locking of Photonic Paint.
Optics Letters
21, 650 (1996); de Oliveira, P. C., Perkins, A. E. & Lawandy, N. M. Coherent Backscattering from High Gain Scattering Media.
Optics Letters
21, 1685 (1996); Balachandran, R. M. & Lawandy, N. M. Understanding Bichromatic Emission from Scattering Gain Media.
Optics Letters
21, 1603 (1996). Notably, the inventor was a contributor to each of these articles. Potential applications include identification, remote sensing, displays, and photodynamic therapy, to name a few (see, for example, Balachandran, R. M., Pacheco, D. P. & Lawandy, N. M. Photonics Textile Fibers.
Applied Optics
35, 1991 (1996); and Lawandy, N. M. ‘Paint-On Lasers’ Light the Way for New Technologies.
Photonics Spectra
28, 119 (1994).
Reference can also be had to the following U.S. Patents, wherein the present inventor is either the sole inventor or a co-inventor: U.S. Pat. No. 6,100,973, Methods and apparatus for performing microanalytical techniques using photolithographically fabricated substrates having narrow band optical emission capability; U.S. Pat. No. 6,088,380, Method and apparatus for intracavity pixelated lasing projection; U.S. Pat. No. 6,030,411 Photoemitting catheters and other structures suitable for use in photo-dynamic therapy and other applications; U.S. Pat. No. 5,903,340, Optically-based methods and apparatus for performing document authentication; U.S. Pat. No. 5,448,582, Optical sources having a strongly scattering gain medium providing laser-like action; and U.S. Pat. No. 5,434,878, Optical gain medium having doped nanocrystals of semiconductors and also optical scatterers.
Motivated by the number of such applications, interest has grown in methods to externally control the random laser line-width, intensity, and emission wavelength. The wavelength can be controlled by mechanisms that affect the chromophore emission wavelength, while the line-width and intensity are most directly affected by the sample volume and the scattering length of the active medium. This was previously presented by the inventor and others: Balachandran, R. M., Lawandy, N. M. & Moon, J. A. Theory of Laser Action in Scattering Gain Media.
Optics Letters
22, 319 (1997). Tuning of the output wavelength of a random laser has been demonstrated using a dye dissolved in a polymethylmethacrylate matrix. The 5 nm wide emission could be tuned by over 30 nm and was observed to be linear from 77K to 380K with a slope of approximately 0.09 nm/K, as described in International Patent Application No.: WO 00038283.
It has been proposed to use liquid crystals to control the properties of photonic bandgap crystals, as discussed by Busch, K. & John, S. Liquid-crystal photonic-band-gap materials: The tunable electromagnetic vacuum.
Physical Review Letters
83, 967 (1999). This approach relies on the different optical properties of the various partially ordered liquid crystal phases that exist at various temperatures. The most dramatic effect on the scattering length occurs with the transition from the birefringent nematic phase to the isotropic phase. Unfortunately, the use of this approach for controlling a random laser is limited by the solubility of laser dyes in liquid crystal materials, requires a solid host structure and has a very small range of scattering length variation. This latter parameter is the critical factor in determining the threshold, linewidth, and output of the random laser.
SUMMARY OF THE PREFERRED EMBODIMENTS
The foregoing and other problems are overcome, and other advantages are realized, in accordance with the presently preferred embodiments of these teachings.
A random laser system includes Critical Solution Temperature (CST) material, either a Lower CST (LCST) or an Upper CST (UCST) material, in combination with an optical gain medium, such as a laser dye. A laser-like emission is observed in response to optical pumping only when the CST material is in a scattering state. The random laser is suitable for being microencapsulated, and can be used for, as examples, remote temperature sending applications as well as for visual display applications.
A system is disclosed for creating a random laser media, where the scattering wavelength predictably relates to the temperature of the media. This invention may be used in a variety of applications, such as for the remote sensing of temperature. A preferred embodiment of this invention employs a LCST material as a scattering phase, in combination with an optical gain medium that includes a dye, such as a laser dye.
In a preferred, but non-limiting, embodiment of this invention a random laser action media is formed from a combination of hydroxypropyl cellulose (HPC) as the LCST material and the laser dye known as Kiton Red 620, where the laser dye is dissolved into the HPC. The resulting random laser action media exhibits a temperature dependent shift in scattering wavelength that is both predictable and reproducible.
In accordance with these teachings a random laser is provided within a container that contains an optical gain medium in combination with a LCST material. The random laser, when pumped by an external source, has an emission that exhibits laser characteristics only when a temperature within the container is above the LCST of the LCST material.
The container may be a capsule having a size of microns or tens of microns, and a plurality of such capsules can be disposed within a coating upon an object. In another embodiment an optical filter can be used, and the emission passes through the optical filter. The gain medium may be a laser dye, and the LCST material may comprise an aqueous hydroxypropyl cellulose (HPC) system.
A method is also disclosed for remotely sensing the temperature of an object. The method includes providing the object wit
Harrington & Smith ,LLP
Menefee James
Spectra Systems Corporation
Wong Don
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