Wavelength dependence of photothermal deflection in Au/Si bimaterial microcantilevers

[Display omitted] •Role of incident laser parameters (λ, power and frequency) on the deflection response of Au/Si microcantilevers is studied.•Increase in deflection sensitivity with decreasing wavelength is explained on the basis of associated temperature rise.•Temperature rise at the free end of microcantilever is independently validated through micro-Raman thermometry.•A deflection sensitivity of ∼ 0.13 pm/nW (equivalently ∼109 μK/pm) was achieved.•Deflection sensitivity is compromised, when modulating frequency of the incident laser is greater than 100 Hz. In the present work, effect of incident laser parameters (wavelength, power and modulating frequency) on the photothermal deflection response of Au/Si bimaterial microcantilevers (MCs) is investigated. Wavelength dependent studies were performed by exposing the free end of Au coated Si MCs to five different laser diode sources (406 nm (UV) – 984 nm (near IR)), at constant laser power of 2 mW. Dynamic response and incident laser power dependence studies were performed by varying the modulating frequency (DC to 2 kHz) and power of the actuating laser, respectively. MC deflection response was found to reduce with increasing wavelength and is explained on the basis of wavelength dependent absorptivity of the exposed MC surface and the corresponding temperature rise at the free end of MC. Experimental results were compared with various theoretical models and were found to be in good agreement when heat dissipation to the environment, through convection losses, was included. Similarly, at a given wavelength, MC deflection magnitude was found to roll off for laser modulating frequencies > 100 Hz. These observations are explained on the basis of reduction in absorbed power per unit time at high frequencies, which in turn reduces the temperature rise. Temperature rise at the free end of MC was independently estimated from micro-Raman measurements and corroborated with MC deflection measurements.