Depth of penetration of an 850nm wavelength low level laser in human skin.

Low Level Laser Therapy is used for a wide variety of conditions including superficial skin sores, musculoskeletal and joint problems, and dentistry. Knowledge of the penetration depth of laser radiation in human skin is an essential prerequisite to identifying its method of action. Mathematical simulations and estimates from the literature suggest that the depth of penetration of laser radiation using wavelengths from 630nm up to 1100nm may be up to 50mm. The aim of this study is to directly measure the penetration depth of a Low Level Laser in human tissue. Human abdominal skin samples up to 0.784mm thickness were harvested by dermatome following abdominoplasty procedures. These samples were irradiated by a Gallium Aluminium Arsenide Laser (Wavelength 850nm near infra-red invisible light, 100mW, 24kHz, 0.28mm diameter probe) and the transmitted radiation measured with an Ophir Optronics 'Nova' external energy meter. The intensity of laser radiation reduced by 66% after being transmitted through a 0.784mm sample of human abdominal tissue. In this study most laser radiation was absorbed within the first 1mm of skin.

Monitoring the ups and downs of pulsed dye laser energy output.

The internal energy meter reading of a Chromos pulsed dye laser (PDL) set at 50% of maximum pumping energy was recorded at the start of every clinical session over an 898 day period and compared with the measurement from an Ophir Optronics 'Nova' external energy meter. This quick and inexpensive process improved quality control procedures for the use of the PDL and enabled the performance of laser components such as the dye, pumping mechanism and optics to be monitored. The stability of the laser output energy was also monitored during three simulated clinics on days 665, 870 and 898. External energy meter readings were recorded every 100 pulses during each simulated clinic comprising six series of 500 pulses. As the energy output was shown to be stable during each clinic (SD<4.7%) recalibration during treatments of up to 500 pulses with this laser was deemed to be unnecessary. However, it was noted that this output energy stability was maintained by varying the pumping energy from 42 to 88% of maximum. Subsequent measurements of pulse width conducted with an ET-2000 Silicon Photodetector demonstrated that although the nominal pulse width was 450 mus, this varied from 240 to 390 mus as the pumping energy increased from 20 to 50%.