Jürgen Eichler

A Review of Different Lasers in Endonasal Surgery: Ar-, KTP-, Dye-, Diode-, Nd-, Ho- and CO2-Laser

Summary Background and Objective: Endonasal laser surgery is presently performed by seven different laser types with wavelength ranging from about 500 nm to 10.600 nm. It is the purpose of this study to review the clinical applications and to discuss the advantages and problems of each specific laser. Materials and Methods: The interaction of laser radiation and tissue is compared for different laser systems. Clinical applications of endonasal laser surgery are reviewed. Results and Discussions: Absorption and scattering of radiation in tissue depend on the wavelength of the radiation. This has a considerable influence on the radiation field and the temperature distribution during surgery. Different coagulation and evaporation zones arise for each laser system. The study shows that all of these lasers yield good clinical results. This is probably due to the fact that the surgeons properly adapt the power density and the movement of the beam over the tissue.

Nonlinear scattering in hard tissue studied with ultrashort laser pulses.

The back-scattered spectrum of ultrashort laser pulses (800 nm, 0.2 ps) was studied in human dental and other hard tissues in vitro below the ablation threshold. Frequency doubled radiation (SHG), frequency tripled radiation and two-photon fluorescence were detected. The relative yield for these processes was measured for various pulse energies. The dependence of the SHG signal on probe thickness was determined in forward and back scattering geometry. SHG is sensitive to linear polarization of the incident laser radiation. SHG in human teeth was studied in vitro showing larger signals in dentin than in cementum and enamel. In carious areas no SHG signal could be detected. Possible applications of higher harmonic radiation for diagnostics and microscopy are discussed.

Holographic quantum eraser experiment reveals polarization structure of depolarized light

It is shown that a holographic setup for real-time interferometry can be used to realize a quantum eraser (QE) experiment. Circular polarized light is used to distinguish between the photons of the reconstructed image of the object and the direct object wave consisting of scattered photons from the illuminated flat object. To erase the which path information, a linear polarizer is used. The experimental results show that polarized light, after depolarizing reflection from a dielectric surface, contains an internal polarization structure, which can be described extending the well-known Jones vector formalism.

Polarization experiments in holographic interferometry

Experiments of real time holographic interferometry were performed with circular and linear polarized laser radiation. An object with a metallic and dielectric part of the surface was studied. It was found that holographic interferometry on the metallic surface can easily be understood with different combinations of the polarization of the different waves. However, unexpected results were found for experiments with the dielectric. The experiments can be explained assuming that the object wave of a diffuse scattering dielectric is different for illumination with right and left circular polarized radiation. Thus, the interference structure of a hologram originating from these waves is also different, in spite of the fact that the image of the object seems to be the same. A theoretical analysis can be performed extending the well-known Jones matrices for radiation depolarized by dielectrics. Theoretical and practical consequences are discussed that refer to the polarization structure of light and to holographic interferometry.

Einführung in die Gewebeoptik und optische Dosimetrie

Zusammenfassung Die raumliche Strahlungsverteilung in der Lasermedizin wird durch die Strahlparameter, wie Laserleistung, Bestrahlungszeit, Bestrahlungsgeometrie, und die optischen Eigenschaften des Gewebes gegeben. Die Bestrahlungsstarke (irradiance) E (in W/m b ) beschreibt den geschwachten Laserstrahl im Gewebe. Dagegen schliest die diffuse Bestrahlungsstarke (fluence rate) Ф (auch in W/m b ) auch die Streustrahlung mit ein. Die elementaren Grosen der Gewebeoptik sind der Absorptionskoeffizient µa, der Streukoeffizient µs und der Anisotropiefaktor g. Daneben werden abgeleitete Grosen wie totaler Schwachungskoeffizient ut, reduzierter Streukoejfizient us, effektiver Schwachungskoeffizient ueff, mittlere freie Weglange eines Photons d und Eindringtiefe der Strahlung δ benutzt. Weitere Begriffe sind die diffuse Ruckstreuung Rd und der Ruckstreufaktor k. Es wird eine Ubersicht uber diese Grosen und die Beziehungen untereinander gegeben. Im eindimensionalen Modell fallt die diffuse Bestrahlungsstarke Ф naherungsweise exponentiell mit der Eindringtiefe δ ab. An der Oberflache gilt Ф = kE. Dieses Modell wird mit den Ergebnissen eines Rechenprogramms verglichen, das auf dem Verfahren der Finiten Elemente beruht.