Abstract
We describe a spectroscopic technique called interferometric photothermal spectroscopy (IPTS) that can measure the absorption coefficient of pulsed laser radiation in nonscattering tissue samples. The technique is suitable for measuring effective absorption coefficients from 10(3) to 10(5) cm(-1). IPTS is particularly attractive because it requires minimal disturbance of the sample. These features indicate potential use for in vivo measurements of tissue absorption coefficients. To validate the technique, the absorption coefficient of pulsed Q-switched Er:YSGG (2.79-microm) radiation in pure water was measured to be 5200 (+/-500) cm(-1) when IPTS was used, in agreement with other published values. IPTS was also used to measure the absorption coefficient of pulsed ArF excimer laser radiation (193 nm) in bovine corneal stroma (in vitro), giving a value of 1.9 (+/-0.4) x 10(4) cm(-1).
Highlights
There is strong interest within the medical community in developing minimally invasive techniques for probing living tissue
We have developed a novel technique called interferometric photothermal spectroscopyIPTSfor measuring the absorption coefficient of pulsed laser radiation in nonturbid tissue samples or the effective absorption coefficient in turbid samples
The fact that the a values obtained from the various traces agreed with one another indicates that the model is a correct description of the dynamics of Er: YSGG laser irradiation of tissue and can be used to estimate a for similar laser–tissue interactions
Summary
There is strong interest within the medical community in developing minimally invasive techniques for probing living tissue. The thermal response of tissue to pulsed laser irradiation can be used to obtain information about tissue thermophysical properties and structure. An example of this is pulsed photothermal radiometry in which the radiative emission from a tissue sample heated by a laser pulse is used to infer the depth, location, and absorption of tissue chromophores.[1,2] We have developed a novel technique called interferometric photothermal spectroscopyIPTSfor measuring the absorption coefficient of pulsed laser radiation in nonturbid tissue samples or the effective absorption coefficient in turbid samples. In IPTS an interferometer is used to measure surface displacement resulting from thermal expansion induced by a pump laser pulse This interferometer is similar to an instrument developed by
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