#3-1. History of medical laser in the 1980s

Following the introduction of the concept of laser in 1917 by Albert Einstein (1879-1955), Maiman developed the world’s very first laser (ruby) in 1960. In the early 1960s, Dr. Goldman showed the possibility of laser’s application in medicine and laser’s clinical safety was established through numerous studies. In 1983, Dr. Richard Rox Anderson (dermatologist) pioneered the theory of selective photothermolysis in his study published in Science¹, which opened an era of rapid and extensive development of medical laser in both theory and practice. Based on the theoretical basis of selective photothermolysis, the second generation of lasers have enjoyed a hay day in the field of aesthetic dermatology from the mid 1980s to present.

Dr. Anderson, who led the era of second generation medical lasers, earned a degree in physics from MIT in 1972 and went on to work as an assistant to Dr. John A Parrish at Harvard Medical School. Anderson at the time was still planning to continue his studies in physics at the graduate school of MIT. However, meeting Parrish changed his course of life, which changed the course of history for medical lasers. Parrish was one of the scholars studying psoralen (plant-extracted photosensitizer) and PUVA (psoralen and ultraviolet A radiation) at the medical school. He wanted to study laser or light sources that stimulates psoralen. Anderson with his background in physics was a great addition to the research team who soon started producing important results.

The first important result was related to skin optics, that is, the interaction between the skin and light. The paper on this subject was published in 1981² and was the very first report on the wavelength-dependent absorption coefficient of melanin, the most important aspect of treating pigmented lesions. Melanin in the epidermis absorbs wavelengths in the range of 250-1200nm, with a greater absorption in short wavelength rather than long wavelengths. According to their paper, short-wavelength visible light was more effective in treating epidermal pigmented lesions compared to long-wavelength infrared light.

Long wavelengths exceeding 1200nm are not absorbed in melanin and reach the dermis without the function of infrared filter. Moreover, they also found that the ultraviolet light with short wavelengths fails to penetrate into the dermis due to scattering, whereas near infrared light with long wavelength can penetrate into the dermis. Their finding is significant in that it provided the first guideline for selecting the right type of laser for pigment treatments.