Sensing photoacoustic waves brings a lot of loss since the detector distance is in the order of millimeters which also leads to noise in the measured signal. To solve this problem, we used an optically trapped silica particle as a transducer in this study. We used two laser sources, one for optical tweezers (976 nm, CW) and a fiber laser for photoacoustic imaging (SHG output: 532 nm, pulsed). The fiber laser was produced in our laboratory whose pulse duration is 8 ns, pulse energy is 10 µJ, and pulse repetition frequency is 65 kHz. The separation between them in the sample plane is 8 µm. The green laser excited several absorbing mediums such as trypan blue, horse hair, black ink and gold thin film. We tracked the position of trapped silica particle (5µm diameter) when the green laser is on and off. We observed dramatic difference between two states. We have validated that this effect is fully photoacoustic by changing the frequency of the green laser with a chopper which led to the exact same frequency when we calculated the Fourier transform of the position distribution of the trapped silica particle. Also, when we change the power of the green laser, the amplitude of the Fourier transformation of the position distribution of the trapped silica particle changes in the same way.
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