Manufacturing Bits: Jan. 28

Fast photography; measuring light waves; counting photons.


Fast photography
The California Institute of Technology has developed a high-speed camera that can take pictures of transparent objects.

The technology, called phase-sensitive compressed ultrafast photography (pCUP), can take up to 1 trillion pictures per second of transparent objects. Potentially, the technology from Caltech could be used in several applications, such as taking photos of shockwaves and neurons in the brain.

Ultrafast photography is emerging. Last year, Caltech and the Institut national de la recherche scientifique (INRS) in Canada developed the world’s fastest camera. The camera, called T-CUP, is capable of capturing ten trillion frames per second.

Phase-sensitive imaging isn’t new. It is used in biological microscopy, optical metrology and astronomy.

In a new twist, Caltech combined phase-sensitive dark-field imaging with compressed ultrafast photography (CUP). This in turn results in a technique called pCUP.

“CUP is based on the compressed sensing theory and the streak camera technology to achieve receive-only single-shot ultrafast imaging of up to 350 frames per event at 100 billion frames/s (Gfps),” according to researchers from Caltech in Science Advances, a technology journal. “Since CUP operates as a passive detector, it can be coupled to many optical imaging systems.”

With pCUP, Caltech has overcome those limitations. The technology consists of a dark-field microscope and a lossless-encoding CUP detection system. This in turn can image phase signals with a noise-equivalent sensitivity of 3 mrad and at 1 trillion frames/s (Tfps), according to researchers.

Researchers have also demonstrated the technology. They imaged phase signals from transparent beads in immersion oil. In addition, the technology was used to image phase signals induced in a crystal. Finally, it was used to image shock waves in water.

In the future, the neuron activity in brain cells is a potential application. “As signals travel through neurons, there is a minute dilation of nerve fibers that we hope to see. If we have a network of neurons, maybe we can see their communication in real time,” said Lihong Wang, a professor at Caltech.

Measuring light waves
LMU, Max Planck Institute and TU Wien have developed a technology to measure the shape of a laser light wave.

Lasers are used in various applications. For example, a free electron laser (FEL) fires electrons through a long magnetic structure. An FEL is tunable and ranges in various frequencies. They are used for advanced spectroscopy and other applications.

Lasers also have short light pulses. Measuring the shape of the laser light wave with high accuracy is critical. But this is often complex and requires a large experimental setup.

One way to measure an infrared laser pulse is using a wavelength in the X-ray range. A gas is sent through the infrared and X-ray pulse. “The X-ray pulse ionizes individual atoms, electrons are released, which are then accelerated by the electric field of the infrared laser pulse,” according to officials from TU Wien. “The motion of the electrons is recorded, and if the experiment is carried out many times with different time shifts between the two pulses, the shape of the infrared laser pulse can eventually be reconstructed.”

There is an easier way to do this—it can be done with a tiny crystal.

The idea is to measure light pulses in a solid. First, researchers obtained tiny crystals of silicon oxide. The crystals are hit by two different laser pulses.

The first pulse is the one that needs to be measured. This pulse can have a wavelength from the ultraviolet to the infrared ranges.

This pulse is fired and penetrates the crystal, followed by a second pulse. “This second pulse is so strong that non-linear effects in the material can change the energy state of the electrons so that they become mobile. This happens at a very specific point in time, which can be tuned and controlled very precisely,” explained Joachim Burgdörfer of TU Wien.

“As soon as the electrons can move through the crystal, they are accelerated by the electric field of the first beam. This produces an electric current which is measured directly at the crystal. This signal contains precise information about the shape of the light pulse,” according to TU Wien.

Counting photons
The National Institute of Standards and Technology (NIST) has published new ways to measure the efficiency of single-photon detectors (SPDs).

This is a prelude to offering an official calibration service for SPDs. SPDs are used in various applications, including the demonstration of the existence of photons, single-photon interference, among others.

“This is a first step towards implementation of a quantum standard — we produced a tool to verify a future single-photon detection standard,” NIST physicist Thomas Gerrits said. “There is no standard right now, but many national metrology institutes, including NIST, are working on this.

“There have been journal papers on this topic before, but we did in-depth uncertainty analyses and described in great detail how we did the tests,” Gerrits said. “The aim is to serve as a reference for our planned calibration service.”

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