Dear Kevin, In the end, my advice is dependent on what you seek to treat. It is correct to say that the Class 4 lasers used for photobiomodulation (PBM) therapy do not yet have a robust evidence-base. I'm open-minded, yet question the need for high-powered/high-intensity light (with probably sub-clinical rise in tissue temperature) when I know that the lower powers work very well (without the risk of tissue warming in the vast majority of cases).
So, back to what is it that you mostly treat? If it's mostly musculoskeletal conditions in a private practice then that would be different to say lots of pressure wounds in an aged care facility, or a mainly lymphoedema-focused practice. If it's musculoskeletal practice, then I most heartily recommend an infrared wavelength, probably in the range of 810-830nm with a reasonably high power output (say 50-100mW) which is where the evidence mostly lies at present and is congruent with the absorption spectra. I have been using 904nm mid-powered lasers recently with good effect on Msk conditions as well. My personal opinion regarding hands-free is based on the following discussion.
Photons will be reflected at the skin interface. Therefore, not only will you lose an increasing percentage of your photonic energy the further away from your target tissue that you hold the device (depending on Class of laser and the diode divergence) but you will also diminish the amount of photons that may reach the target lesion by having the diode situated away from the skin surface. In the end, you want to optimise the amount of photons that reach your target site thus increasing the potential for a beneficial clinical outcome. So, holding the PBM device stationery and in contact (if possible) and at 90 degrees over the target tissue is better than less accurate methods of application. Scanning of PBM over large areas for example, means that theoretically you will reduce the amount of photons that will affect any given amount of target tissue during the overall treatment duration.
Perhaps these factors (scanning, and at a distance) is why some of the new Class 4 laser need to be of a higher power - that is, to overcome the issue of photon loss. Something to reflect on - pardon the pun!