Flattop laser irradiance profile for stimulation of cutaneous nociceptors

Objective: A nerve stimulator based on a CO2 laser has been developed for use in human pain research. A flattened irradiance profile was generated for safer and more uniform pain stimulation. The pain evoked by the flattened profile was compared to a TEM00 profile. Background Data: The CO2 laser normally operates in TEM00 mode. This is not ideal for thermal stimulation, since the beam will generate a temperature that has a peak in the center of the irradiance profile. This will result in non-uniform activation of nerve fibers. Materials and Methods: A lens system has been designed to redistribute the energy of the beam to produce a flattened supergaussian irradiance profile for uniform heating of the skin. The lenses work by refracting the more intense central part of the beam towards the periphery. Psychophysical techniques were used to compare the pain evoked with a flattop irradiance profile and a TEM00 profile. Results: It was found that the supergaussian beam evokes pain at a lower energy level than a TEM00 beam. Conclusion: A flattop irradiance profile is a safer source than a gaussian beam for evoking pain in human pain studies. © 2008 Mary Ann Liebert, Inc.