There has been the great increase in the number of lasers and their applications in dermatology over recent years.  It is useful to group the lasers by their clinical applications:

1. Lasers for the Treatment of Cutaneous Vascular Lesions

The Pulsed Tunable Dye Laser is currently the treatment of choice for Port Wine Stains and some vascular ectasias.  The wavelength of light is selectively absorbed by haemoglobin.  By using micro-second pulses it is possible to confine thermal injury to blood vessels without heat diffusion to surrounding tissue.
Treatment parameters: Wavelength:                  585 nm
                                    Pulsed duration:             450 ms
                                    Spot size:                  5-10 mm
                                    Fluence:                       5-8 J/cm²

 The original optimistic results in the treatment of Port Wine Stains with this laser have not been maintained.  Multiple treatments are required and although significant lightning occurs in the majority, only a minority clear their Port Wine Stain completely. The major disadvantage of the laser is prominent bruising, but it is safe and can be used in children.  

(ii) Argon Laser
The argon laser is primarily of historical interest now, having been superseded by recent lasers.  The blue green light at 488 and 514 nm is absorbed by haemoglobin and melanin. The long pulse durations of the continuous wave laser result in non-selective thermal injury with a high incidence of adverse reactions.

 (iii) Argon Pumped Dye Laser
The argon laser can be used to pump a dye laser using a rhodamine dye to produce yellow light at 577 nm or 585 nm.  This light is well absorbed by haemoglobin and relatively deeply penetrating.  Some form of shuttering or automated scanning delivery device is needed to shorten the pulse duration to acceptable levels.  In the treatment of facial telangectasia this Laser is preferred to be pulsed dye laser by patients because of the absence of bruising.

 (iv) Copper Vapour Laser
The copper vapour laser is another yellow light source used in a similar way to the argon pumped dye laser. The copper vapour laser emits a train of pulses with the duration of 20 to 25 ns at 10 to 15 Hz.  Because of the very short gap between each pulse of light the biological effect of this Laser is similar to that of a continuous wave laser, (quasi-continuous).

 (v) Frequency doubled Nd:YAG laser
The Nd:YAG laser is a solid state laser emitting light in the infra-red at 1064 nm.  Frequency doubling of the Nd:YAG laser produces green light at 532 nm, half the wavelength of the primary light.  The KTP laser  uses a potassium titanyl phosphate crystal to produce green light.  This is a quasi-continuous laser with individual pulses of 200 ns at 25 Hz.  By shuttering the beam macro pulses of 2 – 50 ms can be delivered.

B. Lasers for leg vein telangiectasia

Leg vein telangiectasias are deeper and larger than vessels in a Port Wine Stain.  In general longer wavelengths and pulse durations are required to produce improvement in leg veins.  In many patients sclerotherapy remains the treatment of choice.

(i) The Long Pulsed Dye Laser
The pulsed dye laser has been modified to deliver longer wavelengths (590 to 600 nm) and pulse durations (1.5 ms).  The ultra-long pulse laser (4 ms) has also been used to treat leg veins.

 (ii) Long Pulsed Alexandrite Laser
This laser emits light at 755 nm and when Q-switched is used to remove tattoos.  Using pulses of 5 to 20 ms leg veins have been treated with this laser.

 (iii) Nd:YAG Laser
The long pulsed Nd:YAG laser (1064 nm with 1 to 50 ms pulses) has been reported to improve leg veins, as has the KTP and long pulsed frequency doubled Nd:YAG lasers at 532 nm.

 (iv) Diode Lasers
A number of diode lasers are now gaining prominence in dermatology.  These lasers are highly efficient and often small portable.  Diode lasers at 800 to 815 nm with 10 to 50 ms pulses have been used to treat leg veins.

 With all long wavelength lasers used to treat leg veins high fluences are required which can cause epidermal blistering unless cooling of the skin is employed.

2. Lasers for the Treatment of Cutaneous Pigmented Lesions  and Tattoos

Because melanin absorbs over broad spectrum a variety of lasers of different wavelength can be used to treat pigmented lesions.  The target of melanosomes within the cell requires pulse durations in the nanosecond domain. Blue-black tattoo pigment is disrupted by nanosecond pulses and the same lasers can frequently be used for the treatment of both pigmented lesions and tattoos.

(i) Q-switched Ruby Laser
This laser produces red light at 694 nm which is deeply penetrating and were absorbed by melanin.  Q-switching produces pulse durations of 28 to 40 ns.  Fluences of  5 to 6 J/cm² are effective in treating lesions such as lentigines and freckles.  This laser can improve blue-black tattoos and some green inks, multiple treatments are necessary.

 (ii) Q-switched Nd:YAG laser
When Q-switched this laser emits light with a pulse duration of 10 to 20 ns.  The primary infra-red light at 1064 nm is most appropriate for blue-black tattoos and dermal pigmented lesions.  The frequency doubled green light at 532 nm can be used to treat epidermal pigmented lesions and some red tattoo inks.

 (iii) Q-switched Alexandrite Laser
This laser emits light at 755 nm with a pulse duration of 100 ns.  It can be used for the treatment of pigmented lesions and blue-black tattoos.  It may be an effective laser for the removal of green tattoos.

3. Resurfacing and Ablative Lasers

(i) Carbon Dioxide Laser
The carbon dioxide laser emits infra-red light at 10,600 nm.  This light is strongly absorbed by tissue water.  The original output from carbon dioxide lasers was continuous, now ultra-pulsed or flash scanned lasers with short tissue dwell times are much more widely used.  The laser can be used in a focused mode with a small spot size and a very high fluence for haemostatic tissue cutting, or de-focused for precise tissue ablation of photo damaged skin.

(ii) Erbium:YAG laser
The Erbium:YAG laser is a recently introduced laser with a wavelength of 2940 nm which is in the mid-infra-red.  This wavelength corresponds to the main peak of absorption by water.  This wavelength has 10 to 15 times greater water absorption than the CO2 Laser. The penetration depth into tissue of the Erbium:YAG laser is limited to a small volume of tissue.  Using fluences of 5 to 15 J/cm² very superficial skin ablation occurs with minimal residual thermal damage.

4. Lasers for Hair Removal

(i) Ruby Laser
The ruby laser is used in long pulse (non Q-switched) mode for hair removal.  Typical parameters are:                                     Wavelength:     694 nm
                                    Pulse duration 0.7 to 3 ms
                                    Spot size:      5 to 10 mm
                                    Fluence:           10 to 40 J/cm²

Repeated treatment of anagen hairs are required to produce hair reduction.

(ii) Alexandrite Laser
The alexandrite laser has a longer wavelength of 755 nm than the ruby laser and is more deeply penetrating.  Pulse durations of 2 to 20 ms are used.  The laser has the advantage of large spot sizes and a rapid repetition rates to reduce treatment times.

(iii) Nd:YAG laser
The Q-switched Nd:YAG laser has been used in combination with a topical preparation containing micro-particulate carbon.  All hair types can be treated but there are insufficient long-term studies to assess response.

A long pulsed Nd:YAG laser can also be used with fluences of 20 to 50 J/cm2 with all hair colours reported to respond.  High fluences with epidermal cooling are needed.

(iv) Diode lasers
Diode lasers have been marketed for hair removal.  Typical parameters are:                                                            Wavelength:                 800 nm
                                    Pulse duration:            5 to 30 ms
                                    Spot size:                  9 mm

The longer wavelength may allow treatment of dark skin types with reduced epidermal absorption.