Laser Power Energy Research Articles

Endophotocoagulation through perfluorodecalin in rabbit eyes

Retinal laser endophotocoagulation through perfluorodecalin was studied in six eyes of three Dutch-belted rabbits after vitrectomy. Both the energy density threshold (EDT/50) and the energy threshold necessary to obtain a therapeutic lesion were evaluated. Both argon and semiconductor diode laser endophotocoagulators were used. The amount of laser power energy and the histology of chorioretinal lesions were similar when photocoagulating through perfluorodecalin, compared to photocoagulation through balanced salt citrate-buffered solution. This experimental study indicates that no extra care is necessary when retinal endophotocoagulation is performed through perfluorodecalin, as long as circular spots are obtained and energy is delivered symmetrically to the target site.

Interstitial laser photocoagulation: Evaluation of a 1320 nm Nd-YAG and an 805 nm diode laser: the significance of charring and the value of precharring the fibre tip

Interstitial laser photocoagulation (ILP) is a new percutaneous technique of thermal destruction (necrosis) of deep-seated tumours, using low power laser energy. Our purpose was to investigate: (i) the effects of different laser wavelengths on the extent of thermal damage produced; and (ii) the role of charring around the fibre tip during ILP. Forty-five normal Wistar rats (250–300 g) had ILP to their liver (exposed at laparotomy) by inserting a 400 μm optical fibre into the liver, and activating the laser at 1, 2 or 3W. This was performed at three laser wavelengths (1064 nm Nd-YAG, 1320 nm Nd-YAG, 805 nm diode) using a clean plane-cleaved fibre, and at two wavelengths (1064 nm and 1320 nm Nd-YAG) using a fibre with pre-charring at its tip. The 805 nm and 1320 nm laser wavelengths produced significantly greater necrosis than the 1064 nm, using a clean fibre tip (mean diameters at 2 W were 21.7 mm, 18.3 mm, 8 mm respectively). Pre-charring the fibre significantly increased the necrotic lesion size at 1064 nm (mean diameter at 2 W was 14.7 mm). Using more strongly absorbed wavelengths (805 nm and 1320 nm) and pre-charring the fibre tip give greater thermal damage during ILP, contrary to previously held views that the optimal wavelength for ILP was 1064 nm in the absence of charring.

LASER FLUORESCENCE OF SAND AND CLAY MATERIALS

Samples of granular materials illuminated with a 20 m Watt (average power) laser energy source at a wavelength of 337.1 nm differed in their fluorescence spectra over a wide range of wavelengths from approximately 380 to 660 nm. The fluorescent yield was usually higher with increased fineness of grain size and with increased concentration of clay (> 10% of under 2-μ grain size). However, sandy soils containing a low content of clay (i.e. < 10%) had a higher yield than the regression estimate. Modifying the fluorosensor for greater resolution at a higher energy level (1 nm bandwidth and 25 m Watt average power) resulted in eight discernible peaks between 384 and 440 nm, at 486 and at 550 nm. Overall fluorescence was markedly increased by removal of Fe coatings from the surface of the grains by a dithionite treatment. Thus, laser-induced fluorescence spectra obtained from various partially vegetated land areas by airborne laser fluorosensing may be influenced by the granular material associated with non-vegetated "open" areas.