Development of the Diode Laser System

Abstracted from the work of T. Oshiro in Low-Reactive Level Laser Therapy – Practical Applications, 1991.

Oshiro explains how early diode lasers were made of gallium arsenide (GaAs), a material that usually produced a beam at 904 nm which was difficult to operate for long periods of time because the diode had a tendency to overheat.

Beginning in 1979, however, experiments were carried out with a new type of diode made of gallium aluminum arsenide (GaAlAs) from which a variety of wavelengths ranging from 720 to 904 mn could be operated in a continuous wave without overheating.

It was learned from the data that there is an optimum wavelength for GaAlAs diodes to be used on human tissue at between 820 and 840 nm because of low water absorption rates in that wavelength zone.

Further wavelength experimentation showed a peak penetration effect at 820-840 mn with a corresponding therapeutic effectiveness of laser beams within that waveband. Experiments also showed that power levels of more than 60 mW per laser diode do not increase effectiveness and add the potential for some undesirable side-effects such as exacerbation of the pain, involuntary muscular spasms, and nerve syncope.

Oshiro reports that a battery-powered hand-held 15mW 830 nm continuous wave “system” containing a GaAlAs diode was first introduced at an international congress known as “Laser Tokyo ’81.”