Summary: Dynamic Measurements of Laser Light Attenuation by Cryogen Film and
Bernard Choi1,2, Guillermo Aguilar1,3, Gracie Vargas2, A.J. Welch2, and J. Stuart Nelson1,3
1Beckman Laser Institute and Medical Clinic, University of California, Irvine, CA 92612
2Department of Biomedical Engineering, The University of Texas, Austin, TX 78712
3Whitaker Center for Biomedical Engineering, University of California, Irvine, CA 92612
The purpose of this study was to investigate the dynamics of laser light attenuation during cryogen spray cooling (CSC).
Two detection schemes were used to approximate collimated and diffuse light transmittance measurements of
continuous-wave ( = 594 nm) and pulsed ( = 585 nm) laser light during application of short (20-100 ms duration)
cryogen spurts on a glass substrate. High-speed video images were also obtained during CSC. Collimated light
transmittance varied considerably during CSC. Comparison of collimated and total transmitted light detection indicated
that the diffuse component was substantial. Light attenuation occurred despite transparency of the liquid cryogen layer.
Light scattering by cryogen results in a diverging laser beam incident on the skin surface. Since specular reflectance at
the cryogen-skin interface may differ for diffuse light, further study of light scattering during CSC is warranted. Due to
the differences in optical properties of glass and skin, experiments on skin need to be performed to extrapolate our
results to the clinical scenario. For dermatologic procedures such as laser port wine stain and vascular lesion removal,
hair removal, and nonablative skin rejuvenation, recommended d are 10-80 ms. This range of d appears to be
appropriate, although more studies are required to arrive at a definite conclusion.
Keywords: cryogen spray cooling, port wine stains, transmittance, dermatology, skin