What Is A Laser?

Posted Friday, September 14, 2007 to INDUSTRY > Medical Devices

Posted by The Original Anti-Aging & Cosmetic Surgery Magazine

There are many lasers available to treat a range of skin problems. Jodi Thiessen explains what they are and how they work.

Laser is an acronym for Light Amplification for the Stimulated Emission of Radiation. Laser light is different to normal light for many reasons. It travels in a synchronized fashion, it retains its intensity over a long distance, it is monochromatic (of the same wavelength/color) and it can be pulsed.

The principle of lasers is based on light absorption. The same as a black car will be hotter than a white car because it is absorbing more wavelengths of light certain target tissues will absorb certain wavelengths of light more effectively. As the laser light is monochromatic the target tissue will take on maximum absorption while the surrounding tissues won't. This allows the target to be isolated and treated.

It's the color in the structure that is absorbing the color of the wavelength. There are absorption spectra (level of absorption of particular wavelengths) that can be out of our normal color vision range.We can't see ultraviolet light but it's there and is absorbed by particular structures. C02 and Erbium lasers emit frequencies way out of our visible range; water is a very strong target tissue for them.

What is a target tissue?

Different wavelengths allow delivery of energy to different structures. These structures are target tissues known as chromophores and for cutaneous laser therapy these are: hemoglobin - (blood both oxygenated and deoxygenated), water, melanin (pigment in hair and brown spots) and protein (tattoos).

As each chromophore absorbs different wavelengths of light, different lasers are used for different treatments. The treatments usually fall into four categories. 1. Resurfacing the skin, minimizing wrinkles and scars (chromophore - water). 2. Vascular lesions such as spider veins (chromophore hemoglobin). 3. Pigmented lesions such as brown spots and unwanted hair (chromophore - melanin) and 4. Tattoos (chromophore - protein).

So why does absorbing light treat a problem?

The light energy is transformed into heat energy. This energy heats the chromophore and causes damage. As a process of absorption it transfers the light energy into heat energy and this heat energy then does all the work. In the case of hair removal it heats up the hair follicle to a critical temperature at which point there is irreversible damage to the hair follicle and only the hair follicle. Surrounding structures will be heated but ideally not to a level where there is irreversible damage otherwise blistering will appear.

For blood vessels the hemoglobin is targeted by green or yellow light as these wavelengths are predominantly absorbed by the blood. The blood in the vessel rises to a critically high temperature, it causes damage, and this causes clotting, coagulation and closing down of that small vessel.

For resurfacing the skin the target tissue is water. The laser delivers enough energy to heat the water in skin, vaporizing it and in turn vaporizing skin tissue.

Similarly with each treatment, the heat causes damage of the target tissue creating the desired result.

However without energy (watts) to deliver the wavelength nothing will happen. More energy increases the heat and damage, so there is a trade off. The more energy used can potentially give a better result but the greater the risk of an adverse result.

As one of the special qualities of laser light is its ability to be pulsed, often the beam can target the chromophore for long enough to heat it, then stop before surrounding tissues absorb too much of the light, then this process is repeated. The duration of pulse is proportional to the size of the target.

A laser is usually named for the internal substance that gives it its specific wavelength and treatment properties. These substances are gas (eg. Carbon Dioxide - C02 laser) liquid (eg. Dye) and solid (eg. Ruby).

The physician needs to assess exactly the appropriate wavelength so as to have the energy predominantly delivered to the chromophore and not to any other structure. For example if the desired result is hair removal and the patient has dark skin and fair white hair, by using a laser that is predominantly absorbed by pigment, the hair follicle won't absorb much of that heat energy,but the skin will.

Similarly, when treating tattoos that are multicoloured, different wavelengths are needed for maximum absorption by each of the different pigments.

History of Laser

Many of the required scientific principles for the advent of lasers were set in place by the 19th and early 20th centuries. Descriptions of wave theory by Maxwell in 1864,quantum theory by Planck in 1905 and atomic structure by Bohr in 1913 paved the way for the future development of this technology.

The true father of lasers was Einstein, who theorized on the stimulated emission of radiation in 1917 as part of his paper on quantum theory.

His theories evolved into practice with the development of masers (Microwave Amplification of the Stimulated Emission of Radiation) by Gordon in 1955 and lasers by Maiman in 1960.

Maiman's initial work with the ruby wavelength ushered in a tide of new lasers over the next few years.

These included the HeNe and Nd:YAG lasers in 1961,the argon laser in 1962 and the C02 laser in 1964.

They were employed as dermatological systems virtually from the time of their introduction.

- Dr Greg Goodman (Australian Doctor, 26 November 1999)

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