Among the various parameters of photography, the continuous imaging of microscopic ultrafast dynamic process needs high frame rate and high spatio-temporal resolution. In current imaging systems, these features are compromised.
However, scientists from Shenzhen University in China have recently developed an all-optical ultrafast imaging system with high spatial-temporal resolution and high frame rate. Because this method is all-optical, it gets rid of the bottleneck caused by scanning with mechanical and electronic components.
The design emphasis of these inventions is nonlinear optical parametric amplifier (OPA). OPA is a kind of crystal. When a desired signal beam and a higher-frequency pump beam are irradiated at the same time, this amplifier can amplify the signal beam and generate another beam, which is the so-called idler beam.
Because the crystal used in this study is nonlinear, the emission direction of idle frequency signal is different from that of signal beam. However, how can such devices play a role in high-speed imaging systems? The answer lies in cascaded operational amplifiers. When the pump beam is activated, the target information contained in the signal beam is mapped to the idler beam through OPA. Because of the different direction of the idler, when the signal beam moves to the next level of OPA cascade, it can be captured by traditional CCD camera.
Just like the water in a waterfall, the signal beam reaches the OPA below, which is activated by the pump beam generated by the same laser source. At this time, a delay line makes the pump beam arrive later, which causes the CCD camera next to the second OPA to take pictures later. By cascading four operational amplifiers, four related CCD cameras and four different pump laser delay lines, scientists have created a system that can take four photos in succession very quickly.
The speed of capturing continuous pictures is limited by how small the difference between two laser delay lines is. In this respect, this system has achieved an effective frame rate of 15 trillion frames per second, thus creating a shutter speed record for high spatial resolution cameras. On the contrary, the temporal resolution depends on the duration of laser pulses that trigger OPA and generate idle signals. In this case, the pulse width is 50fs (millionth of a nanosecond). Coupled with the incredibly fast frame rate, this method can observe ultra-fast physical phenomena, such as air plasma gratings and rotating light fields rotating at 10 trillion radians per second.
This imaging method still has room for improvement, but it can easily become a new microscopic technology. Future research will release the potential of this method and let us have a clearer understanding of ultrafast transient phenomena.
The scientific journal Advanced Photonics published this research report. Anatoly Zayaz, co-editor of the journal, personally introduced: "The team of Shenzhen University demonstrated ultra-fast photographic imaging, and the shutter speed set a record for the fastest time. This research provides new opportunities for ultrafast process research in various fields. "