Compressed Ultrafast Spectral-Temporal Photography

Acquiring ultrafast and high spectral resolution optical images is key to measure transient physical or chemical processes, such as photon propagation, plasma dynamics, and femtosecond chemical reactions. At a trillion Hz frame rate, most ultrafast imaging modalities can acquire only a limited number of frames. Here, we present a compressed ultrafast spectral-temporal (CUST) photographic technique, enabling both an ultrahigh frame rate of 3.85 trillion Hz and a large frame number. We demonstrate that CUST photography records 60 frames, enabling precisely recording light propagation, reflection, and self-focusing in nonlinear media over 30 ps. CUST photography has the potential to further increase the frame number beyond hundreds of frames. Using spectral-temporal coupling, CUST photography can record multiple frames with a subnanometer spectral resolution with a single laser exposure, enabling ultrafast spectral imaging. CUST photography with high frame rate, high spectral resolution, and high frame number in a single modality offer a new tool for observing many transient phenomena with high temporal complexity and high spectral precision.

Figure 1

Principle of compressed ultrafast spectral-temporal photography. (a) Spectral-shaping module selects wavelengths for imaging. (b) Pulse-stretching module stretches the fs laser pulse to the full imaging time. (c) Compressed camera: a DMD encodes the laser beam with a pseudo-random binary pattern. A grating disperses the encoded graphs spatially by different wavelengths. A CCD sensor records the compressed 2D image. Caption: beam splitter (BS).

Figure 2

Ultrafast imaging of light propagation. (a) Three sets of temporal snapshots of flying light pulse. (b) Estimated trajectories of light pulse centers. (c) Snapshots of reflected light pulse. Total frame number, 60; frame interval, 414 fs. The arrows show the light propagation direction. The yellow dashed line presents the boundary of Kerr gate medium (${\mathrm{CS}}_2$). A reflecting mirror is placed out of the medium container with a small gap. The photons outside of the ${\mathrm{CS}}_2$ medium are not recorded due to the absence of the Kerr gate effect. Scale bars: 0.5 mm.

Figure 3

Single-shot spectral image. (a) Spectral imaging of near-infrared dye DyLight@800 and blood samples from 795.21 to 806.60 nm. (b) Average transmittances of power meter (solid lines) measurements and CUST spectral images (scattered points). (c) Principle of ultrafast spectral imaging in a spectral tailoring system. Illumination spectrum is selected via tuning the time delay between the pump and probe pulses generated by the (pulse stretching module) PSM. (d) Four sets of single-shot spectral images with central wavelengths from 796.60 to 805.47 nm. Each column is acquired with one laser exposure. The time delays for the four sets of spectral images change from 4 to 20 ps.