We have applied an electronically tuned Ti:sapphire (ETT) laser controlled with a dual radio-frequency driving (DRD) method to noninvasive measurements of the transmission spectra of a whole human hand in which the bands due to hemoglobin and lipid were identified. Spectra of a human hand that is more than 3 cm thick were obtained in the spectral range from 700 to 1000 nm, allowing one to probe the oxygenation of hemoglobin (Hb). Our study demonstrates that an ETT laser may be used as a potential light source for near-infrared (NIR) spectroscopy in biomedical applications. For the acquisition of NIR transmission spectra of Hb with a good signal-to-noise ratio, the laser emission was programmed electronically to fill up strong absorption bands due to water, and baseline undulation due to detection sensitivity and light scattering. The present study required more stable control of the ETT laser, so we developed the DRD method, achieving high reliability in wavelength (< 0.1 nm) and in intensity (<±2% per average in 10 pulses).
Hidetoshi Sato, Satoshi Wada, Mingyi Ling, and Hideo Tashiro, "Noninvasive Measurement of Oxygenation of Hemoglobin by Direct Transmission of Near-Infrared Energy (700–1000 nm) from an Electronically Tuned Ti:Sapphire Laser Driven by a Dual Radio-Frequency Driving Method," Appl. Spectrosc. 54, 1163-1167 (2000)