Dynamic optical absorption characteristic of human blood in visible- and near-infrared light with variable temperature

The knowledge and data of optical properties of skin tissue are critical for optical diagnosis of dermatosis and laser dermatology. In the wavelengths of visible- and near-infrared region, the major chromorphore for light absorption in human skin is the red cells in blood. This paper presents an experimental investigation for the effect of temperature on the optical absorption of human blood. A testing system was setup for measuring the optical absorption of human blood. In experiments, the human blood was slowly heated in a water bath from room temperature to 80°C at a heating rate of about 0.5-1.0°C·min^-1 and the blood absorption spectra were recorded every 5°C of increase in the blood temperature for a wavelength range of 400-1000 nm. The results at the room temperature captured three major absorption peaks well known in literature, demonstrating the validity of the system. A strong dynamic variation of the blood optical absorption characteristics with temperature has been observed, showing four different patterns of change: (1)small change when the temperature is below 50°C; (2)disappearance of selectivity of the blood absorption with wavelength at 50-58°C; (3)a dramatic increase of the absorption over the most of region at 58-65°C; (4)little change when higher than 65°C. An absorption peak is observed over the wavelength from 800 nm to 1060 nm, though the peak is fairly small and broadened significantly. Such an absorption peak in the near-infrared region may lead to the development of new lasers of long wavelength with deep penetration into the skin.