Biophotonics_Concepts_to_Applications

thickening, varicose veins, vascular lesions, unwanted hair, age spots, surgical and
acne scars, and pigmented lesions. The photorejuvenation process uses intense
pulses of light to ablate a skin area through thermal interactions by inducing
controlled wounds on the skin, thereby stimulating the skin to heal itself through the
creation of new cells. Two lasers that have been used historically in free-space or
direct-beam setups are the Er:YAG laser (emitting at 2940 nm) and the CO 2 laser
(emitting at 10.6 μm). Other sources such as a neodymium-doped yttrium
ortho-vanadate laser also have been used.
To reduce the side effects associated with large-area irradiation, techniques using
tools such as fractional lasers andfiber-coupled lasers have been introduced [ 39 ]. In
thefractional laser technique, the skin is irradiated with a dense array of pinpoints
of light, as shown in Fig.6.24[ 45 ]. This process leaves healthy skin between the
ablated areas so that more rapid healing can take place.
The use of an opticalfiber for transmitting the laser light enables a precise
delivery of this light to a localized skin area. Various types offiber-coupled lasers
are available for research on the basic cell photorejuvenation mechanisms and for
clinical use [ 46 – 52 ]. The following devices are some examples of such lasers [ 39 ].
The particular opticalfibers that are coupled to these sources depend on the effi-
ciency with which thefibers transmit light in the spectral emission region of the
source.

• A Q-switched alexandrite laser emits pulses of 50 to 100 ns duration at a
  wavelength of 755 nm. The spot size emerging from the coupled opticalfiber is
  2 – 4 mm in diameter. This laser can be used for treatment of superficial pig-
  mented lesions and is effective at removing black, blue, and most green tattoo
  inks.


• GaAs-based laser diodes emitting at 808 and 810 nm are effective for treating
  dentine hypersensitivity, venous insufficiency, varicose veins, and hair removal.


• Micropulsed Nd:YAG lasers emitting at 1444 nm are used for fat removal
  during facial and body contouring procedures.


• InP-based laser diodes emitting at 1460 nm are effective for skin treatments
  such as collagen regeneration, removal of surgical and acne scars, and wrinkle
  removal.

Irradiated spots

Tissue

surface

Tissue

volume

Zones of

ablation

Zones of

thermal damage

Fig. 6.24 Concept of the
effects from a fractional laser
treatment

182 6 Light-Tissue Interactions