Solid state UV laser for medical applications

Abstract

Key principles needed for the invention of the laser were discovered in the early 1900's. In 1917 Einstein predicted the existence of stimulated emissionc1,21• Twenty-eight years later, Bloch advanced the principles of population inversion and its effects on radiation c3l . Townes and his colleagues produced the first maser (Microwave Amplification by Stimulated Emission of Radiation) in 1953 c4l. It was an atomic generator of electromagnetic energy at microwave frequencies. SchawlowCSl and Townes predicted the possibility of laser (Light Amplification by Stimulated Emission of Radiation) action by employing a crystal as the active material; two years later Schawlow

proposed the use of ruby as the lasing material. The first laser was demonstrated by T. H. Maiman in 1960 using chromium­doped aluminum oxide, a pale pink ruby. This laser had a wavelength of 694. 3 nmC6l. Lasers generate coherent, focused, monochromatic, high­power light. The first application of a laser in medicine was reported by Goldman in 1962c71• Compared with conventional surgery, laser surgery is much more versatile and precise, and reduces the chance for infections and other complications. The laser has become widely accepted in many specialties and

procedures. one of the most important applications of the laser in medicine is in the area of ophthalmology. Scientists have been studied intensively on laser-tissue interaction. An increased understanding of laser-tissue interaction has led to the use of lasers in treating a wide spectrum of diseases involving both the anterior and posterior segments of the eye. Laser-tissue interaction can be divided into several categories, depending upon the power, pulse duration and wavelength chosenC81• They can generally be grouped into photothermal, photochemical and photoionizing effects. Over the past ten years, laser technology has been increasingly used in ophthalmology. There are several types of laser systems operating at different wavelengths and energy levels in the market. The current applications of lasers in ophthalmology can require up to five different types of lasers including the Excimer laser, Argon ( or Krypton) laser, Dye laser, Infrared lasers (CO2, Er:YAG, HF), and Nd:YAG laser. The ref ore, to achieve all potentialprocedures, ophthalmologists must purchase or have access to up to five different systems. This is very expensive because of duplication costs, and inconvenient because of the need to deal with different companies and suppliers. Furthermore, none of these laser systems are currently compatible with one another due to the wavelength dependent delivery systems.

Current laser systems have additional problems such as the use of gases which are unstable or sometimes dangerous. Excimer lasers, for example, are bulky, require large power supplies, and often need water cooling systems. It would be desirable to develop a compact laser system that allows ophthalmologists to perform many types of surgery. The recent technological advances in laser materials and in frequency conversion techniques (such as optical parametric oscillation (OPO), second harmonic generation (SHG), third harmonic generation (THG), fourth harmonic generation (4HG), fifth harmonic generation (5HG), sum frequency mixing (SFM), and difference frequency mixing (DFM)] make it possible to generate many new coherent laser sources. New nonlinear crystals such as Beta-Barium-Borate (BBO) and Lithium-Borate

(LBO) [see Appendix A] yield high harmonic conversion efficiency over a broad spectrum and make it practical to integrate a multifunctional system which will provide a variety of wavelengths, pulse energy levels, and pulse durations required for ophthalmic applications. Such a versatile laser system could combine with different delivery systems, providing the ophthalmologist with the capability of performing several desired procedures on the eye. The compactness, multifunctionality and portability of the system are major advantages over the fixed wavelength laser presently in use. his thesis describes the solid state UV laser system that has been developed by the author and coworkers using frequency conversion techniques. In the next chapter, laser­tissue interaction and absorption principle will be briefly introduced, and we will review some current ophthalmologic laser systems and how they are used in surgery. In Chapter 3 the properties of LBO and BBO nonlinear crystals are introduced. The improvement of conversion efficiency is also discussed. Chapter 4 details the experimental setup and provides and analysis of the data. Conclusions can be found in Chapter 5.

Notes

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Graduation Date

1991

Semester

Spring

Advisor

Lin, J. T.

Degree

Master of Science (M.S.)

College

College of Arts and Sciences

Department

Physics

Format

PDF

Pages

56 p.

Language

English

Length of Campus-only Access

None

Access Status

Masters Thesis (Open Access)

Identifier

DP0029060

Subjects

Arts and Sciences -- Dissertations, Academic; Dissertations, Academic -- Arts and Sciences

Accessibility Status

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