Spectral filtering in pulsed photothermal temperature profiling of collagen tissue phantoms.

We present an experimental comparison of pulsed photothermal (PPT) profiling in collagen-based tissue phantoms utilizing different midinfrared spectral bands. Laser-induced temperature profiles are reconstructed using a custom optimization code within the customary monochromatic approximation. Both experimental results and a detailed numerical simulation of the procedure demonstrate that, despite the associated reduction of signal-to-noise ratio, appropriate spectral filtering reduces the broadening of temperature peaks and thus improves the accuracy of temperature profiling. For our experimental system, best performance is obtained when applying a long-pass filter with cut-on wavelength at 3.4-3.8 microm. Because our collagen gel mimics infrared and thermal properties of human skin, we believe that this conclusion is transferrable to PPT radiometric profiling of human skin in vivo.