Photon Counting Elastography

We demonstrate a non-contact elastography with low-intensity illumination, mode-selective single photon detection, and acoustic excitation. It probes target samples with milliwatt, picosecond laser pulses and measures the backscattered photons via quantum parametric mode sorting and upconversion detection. As the acoustic frequency is swept, the samples' vibrational responses are mapped onto the photon counting histograms from which their mechanical properties--including elasticity--can be derived. By lateral and longitudinal laser scanning at a fixed frequency, an elastogram can be reliably reconstructed upon photon level signals. This technique has the potential for remote sensing and imaging of tissues and materials with differential mechanical properties in photon starved or restricted environment.