26 June 2017

In one quadrillionth of a second

The new femtosecond camera allows you to take pictures of biological processes occurring inside living cells


Researchers from the St. Petersburg National Research University of Information Technologies, Mechanics and Optics (ITMO) have created a new installation, which is a femtosecond camera that allows you to shoot everything that happens inside living cells at great speed. This camera works by analyzing the distortions of the femtosecond laser pulses that have passed through the sample under study, and in the resulting images you can see all the smallest details without the need to use special contrast agents.

The processes of vital activity of living cells are complex sequences of biochemical reactions and physical processes, some of which take place at a fairly high speed. Electron microscopes are usually used to study such processes, but this requires the use of special coloring agents that make the images more contrasting. In addition to improving the quality of images, the use of agent substances can have a negative effect on the metabolism of the studied cells. New digital holographic microscopes do not have the drawback mentioned above, but they provide low-resolution images.

The new camera, created by scientists from ITMO, allows you to register even the fastest biochemical processes by adjusting its resolution. Its only limitation is that the samples under study must be transparent. The device synthesizes images based on data from the analysis of distortions of the femtosecond laser light pulse that occur when it travels through an object, and the main data source is the phase shift of light. 

Drawings from the New femto-camera press release
with quadrillion fractions of a second resolution
– VM

The initial pulse of laser light is split into three beams before use. The first beam contains 95 percent of the total pulse energy, and this beam is used for diagnostic and calibration purposes. The second beam passes through the test sample, and the third is directed past the sample using a system of mirrors. The second beam that passed through the sample and the third, acting as a reference, are folded, and a holographic picture appears at the place of their superposition, consisting of a series of maxima and minima of light waves. 


By changing the position of the mirrors, you can force the reference beam to come to the "meeting place" with a certain delay. In other words, the beam that has passed through the sample under study is scanned using a reference beam. Each step of such scanning generates another holographic image and a series of these images turns into an image using a fast computer algorithm.

Scientists from ITMO are going to continue working on improving the camera they created. But even in the form in which it exists today, it already represents a very powerful scientific tool. In addition to the fact that the new camera outstrips all available similar tools in terms of speed and resolution, its design is much simpler than the design of any of the powerful modern microscopes.

Article by Petrov et al. Time-resolved image plane off-axis digital holography is published in the journal Applied Physics Letters – VM.

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