Coherent light generators – Particular active media – Amorphous
Patent
1984-12-11
1987-02-17
Scott, Jr., Leon
Coherent light generators
Particular active media
Amorphous
372 35, 372 42, 372 10, 372 5, H01S 317
Patent
active
046445501
DESCRIPTION:
BRIEF SUMMARY
The invention refers to a liquid cooled neodymium-phosphate glass-impulse laser with passive Q-switching, which can be fabricated to a small size, in a portable version and is mainly intended to be used in medicine, particularly in eye operations, furthermore in Spectroscopy, cosmetics, for teaching and in Microtechnology. The laser in the invention makes it possible to generate impulses in the TEM.sub.00 -mode with an impulse length lying below 20 ns, with an angular divergence amounting to less than 3 mrad, with energy boostable up to 50 mJ and with a maximum repetitive frequency, where the wave-length of the coherent light impulses is 1.054 .mu.m.
The repetitive frequency of the laser impulses can be continuously varied up to the maximum values. The cooling of the laser head is accomplished with cooling liquid in a closed circuit. The device can be switched into the normal single phase power supply, its power consumption is typically 50 W, its overall weight approximately 2 kg.
The utilization of photocoagulators is known in eye therapy. Earlier on Xenon-lamp devices were used, whose long exposure periods (250-1000 ms) required a special anesthesia. Apart from that in most cases the focused light spot diameter (500-1000 .mu.m) attainable at the retina is too large. In order to remove these disadvantages laser photocoagulators were developed, with which it is possible to concentrate the light beam of the laser upon a considerably smaller area, in the optimal case having a diameter smaller than 10 .mu.m. Thus the desired biological action is achievable with impulse lengths smaller by several orders of magnitude, thus a special anesthesia is superfluous, it suffices to immobilize the head of the patient and to use means for dilating the pupils. For the successful treatment 1 to 5% of the energy of the light impulse of a Xenon-lamp is sufficient, often even a considerably smaller amount of energy.
In the previous phase of utilization ruby lasers functioning in impulse operation were primarily used, today on the contrary glass lasers designed with ionized Ar or Kr operating continuously are in wide use. With these the exposure periods are comparatively long, of the order of magnitude of 0.1 s, but their light can be focused relatively well. The disadvantage: since the exposure time is short in relation to the operating period, the light energy radiated by the laser is utilized only to a small extent.
Because the energy of the laser impulses utilized for the treatment--and with this also the undesirable side effects--can be reduced by a reduction of the impulse duration, there can be observed in the last two years a growing interest in solid body lasers, primarily in Q-switched, or in mode synchronized Nd:YAG-lasers. The price of these equipments is, however, very high, together with a device for immobilizing the head of the patient and the aiming optics which focus the laser light on the desired spot of the eye, it is of an order of magnitude of 100 000 U.S. dollars. Their dimensions are, however, very large, thus their application is essentially possible only in stationary versions, because besides the considerable weight their current consumption is also very high and generally requires cooling from the existing water mains. Information about these systems can be found in the publications LASER FOCUS (February 1983) and LASERS AND APPLICATIONS (October 1982).
The aim of the present invention is the realiztion of such a laser, which excludes the above-mentioned disadvantages and the creation of an inexpensive, portable device, which can be plugged into the normal single phase power supply and comprises a closed circuit cooling system, which will have broad utilization particularly in eye therapy.
The invention is based on the finding that the Nd-ions can be introduced in high concentrations into the lithium phosphate glass, with which a 2-3 times higher efficiency of the laser function can be achieved on a wavelength of 1.054 .mu.m with typically a 3-5 times smaller beam divergence, than with an Nd:YAG-lase
REFERENCES:
patent: 4022707 (1977-05-01), Deutschbein et al.
patent: 4371965 (1983-02-01), Lempicki et al.
Csery Huba
Czigany Imre
Horvath Zoltan
Kertesz Ivan
Kroo Norbert
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