Coherent light generators – Particular beam control device – Producing plural wavelength output
Reexamination Certificate
2001-02-27
2003-04-01
Leung, Quyen (Department: 2828)
Coherent light generators
Particular beam control device
Producing plural wavelength output
C372S053000
Reexamination Certificate
active
06542524
ABSTRACT:
FIELD OF THE INVENTION
The invention relates generally to the field of solid state lasers and more specifically to improved methods and devices for converting a pump laser beam to an output beam of a desired wavelength.
BACKGROUND OF THE INVENTION
A wavelength conversion device enables standard single wavelength lasers to perform multiple functions. One application of a wavelength conversion device is to use a common medical laser as a pump laser and to produce output wavelengths in the 570-850 nm range. Such a device can be used to facilitate a variety of medical therapies, such as in ophthalmology for retinal photocoagulation, illumination of photodynamic therapy (“PDT”) drugs for the treatment of Age Related Macular Degeneration (“AMD”) and other disorders, and transpupilary thermo therapy (“TTT”).
When a laser is used to treat diseases of the eye, the laser's power and output wavelength(s) need to be carefully controlled. The wavelength of a laser must be matched to the absorption of a particular PDT drug to stimulate its effect. Ophthalmic laser therapies require a variety of visible and near-infrared wavelengths, depending in part on the desired depth of beam penetration. Ophthalmic PDT treatment of AMD requires about 300 mW of continuous wave laser power.
PDT drugs are typically illuminated with semiconductor diode lasers which output beams with wavelengths in the range of 630-810 nm. A drawback to the use of semiconductor diode lasers for illumination of PDT drugs is that a given diode laser is limited in the wavelength range it can produce. Typically, a single diode laser can provide on the order of 5 nm of wavelength range. Therefore, many diode laser devices would be required to illuminate all possible PDT drugs.
Laser pumped dye lasers can readily provide tunable output beams ranging from blue-green wavelengths in the visible range to near-infrared wavelengths. Laser pumped dye lasers can also be used to create typical PDT wavelengths, but are more typically used in non-ophthalmic PDT applications where an output beam with a higher power is desired. Argon ion lasers are used to optically pump an organic dye liquid in either a continuous or a rapidly pulsed mode of operation. Ultraviolet or green solid state lasers are also used to pump liquid dye lasers, typically in a pulsed mode of operation. Due to rapid decomposition of the dye, thermal-optical effects and triplet state absorption, these dye lasers have fluid circulation systems to refresh, filter and rapidly flow the dye through the lasing area. In many cases, these organic laser dyes are dissolved in solvents, which results in operational and safety problems.
The operational problems associated with liquid dye lasers have spurred research into the development of solid state dye lasers, which can be made by impregnating a variety of materials with laser dye. A solid state laser made by impregnating laser dye into a polymer can produce an optical performance comparable to that of a liquid dye laser. (See, e.g., R. Hermes, T. Allik, S. Chandra, J. Hutchinson,
High Efficiency Pyrromethene Doped Solid State Dye Lasers
, in Appl. Phys. Lett. 63(7), p. 877 (Aug. 16, 1993).) Unfortunately, results to date show that there are significant limitations to the useful lifetime of dye impregnated solid material and severe thermal optical aberrations in the solid dye laser material. (See, e.g., T. Allik, S. Chandra, T. Robinson, J. Hutchinson, G. Sathyamoorthi and J. Boyer,
Laser Performance and Material Properties of a High Temperature Plastic Doped With Pyrromethene-BF
2
-Dyes
, in Mat. Res. Soc. Symp. Proc. Vol. 329, p.291 (1994).)
Techniques such as moving the laser media have been used with solid state crystalline or glass lasers to reduce the average heat loading in the media, thereby reducing thermally induced optical aberrations. (See U.S. Pat. No. 4,890,289, Fiber Coupled Diode Pumped Moving Slab Laser.) The technique of fabricating the laser medium into a dye impregnated plastic rod and slowly rotating the rod has been proposed. This technique decreased the thermally induced optical aberrations at low pulse repetition rates. (S. Chandra, T. Allik, A. Floener, Compact, High Brightness, Solid State Dye Laser, in OSA Proc. on Adv. Solid-State Lasers, Vol. 24 (B.H.T. Chai and S. A. Payne, eds.), Optical Society of America, 1995.) An example of a rotating plastic-disk dye laser has been described. (A. Bank, D. Donskoy, and V. Nechitailo, High Average Power Quasi-CW Tunable Polymer Laser, in Proc. SPE Vol.2380, p. 292 (R. Scheps and M. Kokta, eds.), 1995). However, none of the foregoing examples has achieved more than limited success.
SUMMARY OF THE INVENTION
According to one embodiment of the present invention, an apparatus converts a pumping wavelength of a pump laser beam to a desired output wavelength. This apparatus includes: a solid medium impregnated with at least one type of laser dye; an input optical coating disposed on a first surface of the medium; and an output optical coating disposed on a second surface of the medium. The input optical coating and the output optical coating are configured to form an optical resonator within the solid medium. The output optical coating is partially reflective at the desired output wavelength and highly reflective at the pumping wavelength.
According to a second embodiment of the present invention, another apparatus converts a pumping wavelength of a pump laser beam to a desired output wavelength. The apparatus includes: a rotating device for rotating a disk-shaped solid medium impregnated with at least one type of laser dye; a resonator to resonate light from a pumped volume of the medium; a first optical coupling device for coupling a pump laser beam having a pumping wavelength to the medium; and a second optical coupling device for coupling a laser beam output from the pumped volume of the medium to an output device. The output laser beam has a wavelength different from the pumping frequency. Preferably, the rotating device rotates the medium at a rate fast enough to clear a volume of the medium heated by the pump laser beam in about 1 &mgr;sec.
An input optical coating may be disposed on a first surface of the medium and an output optical coating maybe disposed on a second surface of the medium. The input optical coating and the output optical coating are configured to form an optical resonator within the solid medium. The input optical coating is transmissive (preferably with R<30%) at the pump wavelength and highly reflective (preferably with R>98%) at the desired output wavelength. The output optical coating is partially reflective (typically 90-99%) at the desired output wavelength and may be reflective (for example, with R>90%) at the pumping wavelength to enhance pump absorption.
If optical coatings are not disposed on the medium to form a resonator and external mirrors are used, antireflective coatings may be disposed on the medium.
The medium may be of any convenient shape, but in the preferred embodiment the medium is disk-shaped and has dimensions which approximate those of a conventional compact disk: about 120 mm in diameter and 1.2 mm thick. This allows the disk to be used in combination with many components of a conventional compact disk player, such as the platter, drive motor and disk changer. If the disk is made of plastic (for example, of dye-impregnated polymer), CD manufacturing molds and processes may be used. The ability to use existing components and manufacturing processes greatly reduces the manufacturing cost of the apparatus.
If the medium is larger than a conventional CD, it may be used for a longer time. Therefore, for some applications it is advantageous to form the medium into a size larger than that of a CD, despite the loss of some efficiencies associated with using a standard CD size.
In one embodiment, the device uses a modified version of the tracking servo found in a conventional compact disk player to move the pump laser beam in a radial direction while the disk is rotating. The tracking servo causes the pump laser b
Beck David G.
Bingham & McCutchen LLP
Leung Quyen
LandOfFree
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