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Laser Components USA, Inc.
116 South River Road
Building C
Bedford, NH 03110
USA
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Photodynamic Therapy

Photodynamic therapy is used in ophthalmology, oncology, and dermatology. Light treatment is advantageous for a patient due to the noninvasive or minimally invasive methods used. It leads to faster healing and recovery than other methods.

Dermatological Treatment with High-Power Laser Diode Systems

If certain wavelengths are required for treatment, we rely on the light of a monochromatic laser.

In dermatology, the absorption of laser light results in an increase in temperature in the treated areas of the body. This rise in temperature, therefore, has to be monitored in order to make sure that the desired temperature is achieved in the intended area, without sustaining damage to the surrounding area.

The wavelengths of laser systems commonly available on the market at 810 nm, 940 nm, and 1064 nm result in a high absorption of light and thus overheating due to the amount of melanin in the skin. This can lead to an increased risk in damage to the surrounding tissue.

Laser systems in the range of 800 nm to 1100 nm are particularly advantageous because they are available commercially at high power levels. In dermatology, it is, therefore, possible to achieve sufficient absorption and depth of penetration to produce the desired reaction.

The application of longer wavelengths at or near 1460 nm is even more advantageous because at this wavelength the absorption of water is at least two orders of magnitude higher than that of melanin and hemoglobin [7]. The depth of penetration of lasers at approximately 1460 nm is absorbed at the depth of the actual subcutaneous target area [8]. The greater absorption thus allows the application of 1460 nm lasers with a smaller power than laser systems in the spectral range of 800 nm to 1100 nm and still achieves the same energy absorption.

During radiation, the energy level applied to the skin plays a crucial role in combination with the chosen wavelength. Effective treatment of an area (i.e., treatment of an area that does not cause undesired damage to the surrounding areas) requires controlled heating of the adjacent tissue. Localized heating can be controlled by turning on and off the laser (pulse duration) at a certain frequency (repetition frequency). During the duration of the pulse, the light is absorbed and the temperature of the target area increases. Heat expands from the target area to the surrounding area. If the pulse duration is too long, the target area and the surrounding area are heated to a point where both areas can sustain damage. Turning off the laser pulse for a certain length of time allows the heat to dissipate and thus reduces the risk of damage to the non-target area. By optimally adjusting the pulse duration and the repetition frequency, the desired temperature range in the target area can be achieved, while maintaining a temperature range in the surrounding area that is low enough to prevent damage.

In addition to optical power and treatment time, the size of the radiated light spot in the tissue plays an important role in treatment. A small spot size releases a high concentration of optical energy onto the radiated surface. While a small spot results in a high concentration of optical energy, the depth of penetration is reduced due to increased dispersion. Larger light spots, on the contrary, are suited for deeper target areas within the skin because they cause less dispersion. At the same time, a larger treatment area can be covered in one session. The disadvantage is a reduction in optical energy applied to the target area.

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