Voltage signal recorded with a wideband focusing ultrasonic transducer (3.5 MHz) in response to pulsed optical irradiation of a light-scattering phantom. Photoacoustic response of a subsurface chromophore with μ a = 2 cm−1 is indicated with the arrow.
Maximum permissible exposure of human skin (solid curve) and exposure level as a function of time for two values of optical irradiance I 0 = 9 W/cm2 (line 1) and 4 W/cm2 (line 2).
Normalized spectrum of a chirped signal with frequency sweep 1–5 MHz and constant amplitude (curve 1) and the spectrum of a chirp weighted according to Eq. (7) with μ a c a = 1 MHz (curve 2). Normalization was done with respect to maximum value.
Result of correlation processing of two chirps with the spectra shown in Fig. 3 and the input SNR = –40 dB. Normalized correlation function of a chirp with constant amplitude (a) and the chirp with spectrum weighted according to Eq. (7) (Fig. 3, curve 2) (b).
Experimental correlation function of a chirped photoacoustic response received from a planar chromophore with μ a = 2 cm−1 immersed in tissuelike Intralipid solution 2 cm deep. Focusing transducer: 0.5 MHz and focus: 5.08 cm; chirp parameters: Δf = 0.2–0.8 MHz, T ch = 1 ms.
Optimization of SNR in frequency-domain chirped photoacoustics with respect to laser power (laser spotsize = 2.8 mm) and chirp duration: (a) safe chirp duration for the given laser power and laser spotsize, (b) SNR as a ratio of correlation peak to noise standard deviation for the laser power and chirp duration varied according to the safety curve.
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