Optical manipulation of the heat flow followed by the thermoelastic photoacoustic response of n-type silicon

• Changes in the heat flow direction in n -type silicon due to changes in its transparency. • Heat flow monitoring through the thermoelastic photoacoustic response of the sample. • Direct correlation between the sample temperature differences and the absorbance values. • Equal effect of excess carriers and direct light-to-heat conversion at red light wavelengths. • Increasing influence of excess carriers at infrared wavelengths. We model and quantify the combined impact of the free carriers and absorption coefficient of n -type silicon on the heat flux generated by its light illumination periodically modulated in time. The light penetration depth is shown to significantly affect the temperature difference between the illuminated and unilluminated surfaces of the sample. Consequently, the frequency response of the thermoelastic component of the photoacoustic signal changes and becomes a reliable indicator of the heat flux variations. Our numerical calculations illustrate how these variations can be achieved by adjusting the wavelength of the light source.