Frequency Domain Non-Contact Photoacoustic Microscopy

We present a non-contact "frequency domain photoacoustic microscope" (Fd-PAM) in which photoacoustic signal is generated by an amplitude modulated continuous-wave (CW) laser and detected at the sample surface using two wave mixing (interferometer) in a photorefractive crystal (PRC). The optical detection eliminates the need for a coupling medium, thus making the probe contactless and mitigates loss in signal-to-noise ratio (SNR) resulting from attenuation associated with wave propagation from the sample to the sensor. The single frequency excitation enables the use of extremely narrow band detection techniques like a lock-in amplifier for noise suppression. Our approach also can image multi-layered specimen and directly produce an image that is equivalent to the maximum-intensity projection of the 3D image volume.