by Prof. /Dr. Mohammad E. Khosroshahi.
Abstract
Combined probe beam deflection (PBD) and wavefront sensor (WFS) techniques are used to investigate the thermal distribution of gold nanourchins (GNU) in physiological saline (PS) using a low-power continuous NIR diode laser. Three different samples were prepared for the experiment: (S1) 0.5 mg/mL GNU only, (S2) 0.5 mL PS and 0.3 mL GNU, and (S3) 0.5 mL PS and 0.1 mL GNU.
The laser transmission initially increases linearly as S3 > S2 > S1 but reaches a plateau and remains constant. The probe beam response in an adaptive statistical process exhibited stochastic behavior at different positions and constant power in the x- and y-directions. The beam view profiles showed a non-uniform intensity distribution, and the addition of PS dramatically caused a blue shift, indicating its cooling effect: S1 (20) warmer > S1 (10) medium > S2 (20) cooler. S1 (10), S1 (20), and S2 (20) correspond to the samples irradiated with the laser power (mW) shown in the brackets.
The peak-to-valley (PV) and root-mean-square (RMS) values demonstrated a non-linear intensity distribution during the scanning process. The greater PV values at deeper positions may well be due to agglomeration, hence the sedimentation process. The Zernike coefficients with high absolute values represent the aberrations that cause the greatest distortion of the wavefront, found in the order of S2 (20) > S1 (10) > S1 (20). This is consistent with the PV wavefront slope and spatial period aberration relation. The opto-thermal coefficients were obtained as follows: S2 (-7.86 × 10⁻⁴) > S3 (0.5 mL PS and 0.1 mL GNU: -6.3 × 10⁻⁴), respectively.