Page 99 - Chapter 3 - Fundamentals of Laser/IPL Hair Removal

Absorption filter
Dielectric filter
Fluorescent filter
- this type absorbs the unwanted wavelengths and converts the light energy into heat within the filter. Most IPL systems use this type of filter.
- this type of filter reflects the unwanted wavelengths out of the filter and does to allow them to transmit through. Hence the filter does not heat up during use.
- this filter absorbs some of the unwanted wavelengths and re-emits them as longer wavelengths. This type is only used in a very small number of IPLs.
Chapter 3 – Fundamentals of Laser/IPL Hair Removal 1st Edition
Another useful aspect of water cooling is that water is a natural filter of IR light (i.e. heat). Since the Xenon lamp generates a large quantity of IR light it must be removed to prevent it reaching the skin surface. Consequently, water-cooled devices are inherently safer than air-cooled systems. The flashlamps in these systems are also likely to last longer than in air-cooled systems.
Multiple Flashlamps
Some IPL systems utilise more than flashlamp in their handpieces. This is simply to increase the overall power output of the unit. These systems tend to use smaller flashlamps than others for operational reasons. The lamps are usually positioned side by side and are fired simultaneously. The only real advantage of such a set-up is that the effective spot size may be a bit larger than a system with only one lamp. It really depends on the dimensions of the handpiece’s light guide.
Filtering the Flashlamp Output
When an IPL system is fired the flashlamp produces a full visible spectrum of light from blue to infrared. In many clinical applications not all of this light is useful – in fact, in some cases it is undesirable.
The way we get around this problem is by the use of filters. These are small devices specially designed to stop the wavelengths we don’t want, thus allowing through those wavelengths which are useful.
For example, for hair removal we only really want the red and infrared light so we use a filter which blocks all the other wavelengths below red (yellow, green and blue). For blood vessels we want the yellow light which is strongly absorbed in haemoglobin; so we block the lower wavelengths in this case. Using the red is fine for this treatment since it does not interfere with the treatment.
There are, essentially, three types of filter available today:
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