Beam broadening in dense scattering media.

The full 3-D integral equation for the spherically symmetric scattering of light in a medium of densely packed uniformly distributed scattering centers is solved for the case of a cylindrically symmetric laser beam (Gaussian profile) directed normally at the slab. After reduction to a 2-D problem, the discretized integral equation for the intensity (irradiance) of the scattered light is solved by a standard iteration procedure. The resulting 2-D distribution is reconverted to 3-D to obtain the r and z dependence of the irradiance. From the solution the angular distribution of backward and forward scattered light is calculated; special emphasis is placed on the radial dependence of the scattered light emerging normal to the surface in both directions. Spot sizes are defined and calculated for various values of beam radius and material parameters, nominally chosen to represent irradiation of white (translucent) biological tissue by a Nd:YAG laser. The effect of increasing the scattering coefficient on the spot profiles and radii is studied.

Endoscopic application of the Nd: YAG laser in urology; theory, results, dosimetry.

We present the results of experimental and theoretical investigations on the interaction of Nd; YAG laser light with biological tissue in general, and with the bladder in particular. A comparison is made between the thermal effects achieved with this laser and those of the argon and CO2 types. A therapeutically safe yet effective dosage for the endoscopic treatment of bladder tumours with the Nd; YAG laser is given. The operating techniques are described along with the first clinical results.

Thermal action of laser irradiation in biological material monitored by egg-white coagulation.

Coagulation of egg white of Nd:YAG and CO(2) laser beams was filmed to illustrate the thermal effect of their radiation and the role of internal scattering caused by the increased structurization of the medium in its non-transparent phase, typical of practically all biological tissue. The purpose was a vivid demonstration of the range of necrosis attainable with these two lasers in surgical and endoscopic applications.

Dosimetry for neodymium: YAG laser applications in urology.

We present the results of experimental and theoretical investigations on the interaction of ND:YAG laser light with biological tissue in general, and with that of the bladder in particular. A comparison is made of the thermal effects achieved with this laser and those of the argon and CO2 types. A therapeutically safe yet effective dosage for the endoscopic treatment of bladder tumours with the Nd:YAG laser is given. The operating techniques are described along with the first clinical results.

Geometrical form factors for the lidar function.

The form factors for the atmospheric backscattering of laser light leaving the exit aperture of a lidar receiving telescope are calculated in the limiting cases of purely geometrical optics and pure TEM(00) laser emission taking axial aperture displacement as well as misalignment of the transmitter axis into account. Some numerical results are plotted, displaying the effects of variations of the telescope's field of view, laser beam divergence, and misalignment.

Thermodynamic analysis of laser irradiation of biological tissue.

A mathematical model is presented for the calculation of the 3-D time-dependent temperature distribution in a biological tissue (slab) irradiated by a laser beam of rectangular or Gaussian profile, which takes into account the different thermooptical properties of the tissue. Detailed consideration is given to the phenomenon of redistributive internal scattering, which is of noticeable magnitude in the irradiation by the argon-ion and Nd:YAG lasers commonly used for tissue coagulation in medicine. Satisfactory agreement is found with temperature measurements performed with a thermocamera, and the CO(2) and Nd:YAG lasers are compared qualitatively and quantitatively.