The light source is typically a flash lamp such as Xenon, and various manufacturers have their own unique protocols of spectral filtering, pulse timing, and beam delivery systems, all optimized for specific types of treatment. IPL sources are not quite lasers, but with many tens of J/cm2 zapping human skin, they can still do serious harm if the system is behaving even a little bit differently than it’s meant to. Even in non-medical, unregulated cosmetic applications, there is a real need to regularly monitor the IPL’s performance. Thermal laser sensors are a standard solution for measuring the energy of a so-called single-shot pulse of light. When it comes to measuring the energy of an IPL pulse, though, there are some unique challenges:
- Broad angular distribution – which makes it difficult to capture the full beam
- Broad spectral distribution – which makes it difficult to maintain accurate calibration
- High energy and energy density – so the sensor’s absorber had better be able to take it, without damage
- Many (if not most) IPL applications involve the use of optical coupling gel on the patient's skin to reduce reflective losses as the light goes from one optical medium (air) to another (skin), by reducing the step size of the refractive index. For the measurement to have maximum clinical meaning, it should be performed under similar optical conditions to those of the IPL's clinical use. That means using gel (or water) on the sensor – without destroying it.