Mark Oksman

Experimental measurement of quality factor enhancement using slow light modes in one dimensional photonic crystal.

We experimentally investigate the effects of slow light modes within a one dimensional photonic crystal resonator. We show that the slow light mode leads to significant increase in the quality factor of the resonator. We provide a theoretical analysis explaining our experimental results. We also include the effect of disorder to simulate the fabrication imperfection. Further results regarding the properties of the one dimensional photonic crystal are discussed.

Current status of flexible waveguides for IR laser radiation transmission

Minimal invasive surgery (MIS) is the preferred method for performing medical operations today due to its lower cost, fast healing, and minimal post-operative pain and discomfort to the treated patients. It is rapidly expanding with the development and miniaturization of two-dimensional (2-D) and three-dimensional (3-D) endoscopic imaging systems. Laser surgery has also proved itself to be a preferred tool of operation over standard tools in a lot of the cases. Development of a reliable flexible fiber or waveguide will enable surgeons to bring the laser beam transcendoscopically within body cavities. It will combine the endoscopy technique with the advantageous laser interaction with tissue to create a powerful surgical tool which will be the ultimate choice of operating procedure. A number of research groups have suggested flexible waveguides for the mid-IR region between 2.5 and 11 /spl mu/m, which contains very important and useful laser wavelengths and is not covered by silica fibers. The chief goals for the development of such delivery devices are summarized. The different solutions suggested are broadly described and thoroughly analyzed for their performance and potential.

Novel copper hollow waveguides for IR laser radiation

Hollow flexible copper waveguides were developed with two types of dielectric layers (Cu2O and ZnS). Measurements of transmission as a function of coupled power have shown that scattering appears in the Cu2O dielectric waveguides which give losses affecting the time of the outlet power which can be maintained constant. Beam profile measurements were performed using the perspex cubes and Spiricon beam profile methods. It was shown that the type of dielectric layer and wavelength of transmitted energy have an influence on the beam profile. The ZnS dielectric layer waveguides have a beam profile with larger average amplitude and less modes as compared to that of Cu2O dielectric layer. The smaller energy per mode of the Cu2O waveguides compared to that for ZnS makes the application of the perspex cubes method not applicable for beam profile measurements for the Er-YAG laser where the average transmitted energy is smaller than that of the CO2 laser, since the energy per mode is not enough to produce traces. It was shown, from the beam profile measurements made with perspex and Spiricon methods on ZnS dielectric waveguides, that when ER-YAG laser radiation is used, by increasing the energy per pulse, is obtained longer traces in perspex or larger energy per pulse than by increasing the time of irradiation. This can have practical applications for the operation of removing tissue with Er-YAG laser. A method of detection if the maximum average transmitted energy is coupled to the center of cross section of waveguide was developed based on beam profile measurements.

Optical measurements of plastic (polyimide) hollow waveguides for IR radiation

Hollow waveguides for infrared radiation are suitable for high power radiation and large interval of wavelengths. This has enabled to begin its preparation for several practical applications in medicine which are already investigated. One of the types of these waveguides is made from plastic (teflon) tubes and several papers were published in this field. Although the Teflon waveguides have several important advantages (high flexibility and biological suitability) for application in medicine, there are also difficulties in achieving low attenuation (low radiation losses), of the transmitted radiation, which is limiting their applications. One of the main reasons of the large losses of the transmitted radiation through these waveguides is the relative large roughness of the internal wall of the tubes which produce scattering of the incident radiation. Several attempts to reduce the roughness have given only a limited improvement since the internal wall of the Teflon tube is not easy to polish (the needed average roughness is less than 10 nm). In previous papers we have reported first results obtained in developing a new type of hollow waveguide for infrared made from polyimide which is a type of plastic with high melting temperature and which can be prepared with very flat surface roughness, less than 10 nm. In this paper we shall present new results of a study made for developing this type of plastic hollow waveguide. The attenuation was reduced to values less than 1 dB. Data about the process of etching for decreasing the roughness of the internal wall of polyimide tube and new methods of deposition of high adhesive and minimal roughness of the Ag and AgI guiding layers will be presented. Results of measurements of attenuation as a function of bending radius, coupled power and time of transmitted radiation will be shown and discussed. New type of dependence of attenuation on bending due to the mechanical properties of the polyimide tubes will be shown and discussed.

Beam profile dependence on conditions of propagation through hollow flexible IR waveguides

A theoretical ray model of IR radiation propagation and delivered beam shape profile of hollow flexible waveguides was developed. Experimental studies of attenuation of coupled CO2 MID-IR laser (wavelength-10.6 micrometers ) and the influence of losses, internal diameter, coupling and scattering on the shape of propagated beam were performed. The theoretical and experimental results have shown a good concordance.

Characterization of copper waveguides for mid-IR radiation with applications in medicine

Copper hollow waveguides with an inner dielectric layer have been developed by using simple techniques of chemical etching and oxidation for the inner wall of the copper tubes. Transmission properties of hollow waveguides have been measured. It is shown, for the first time that a thin Cu2O layer is obtained by using chemical oxidation techniques. It is also shown that the thickness of a Cu2O layer can be controlled by the oxidation time.

Beam profile analysis of waveguide-delivered IR lasers

The study of output laser beam shape as a function of losses, internal diameter, off-center coupling and scattering is presented in this paper. The conditions where the beam shape has good correlation with the source beam shape were found (low losses, center alignment coupling and low scattering). A theoretical model of the mechanism of propagation of the radiation through the hollow waveguides was developed and the conditions under which the shape of beam is changed was calculated. Good agreement between the theoretical and experimental results was found.