Abstract-Hyperspectral terahertz microscopy via nonlinear ghost imaging

Luana Olivieri, Juan S. Totero Gongora, Luke Peters, Vittorio Cecconi, Antonio Cutrona, Jacob Tunesi, Robyn Tucker, Alessia Pasquazi, and Marco Peccianti

Conceptual description of the TNGI approach. (a) Key experimental components and methodology; (b) volumetric representation of the nonlinear generation of THz patterns; (c) fixed-time reconstruction with a field of view 2mm×2mm$2\mathrm{m}\mathrm{m}\times 2\mathrm{m}\mathrm{m}$ and 32×32$32\times 32$ spatial sampling; (d) backpropagated hyperspectral image, averaged between 1 and 2 THz.

https://www.osapublishing.org/optica/abstract.cfm?uri=optica-7-2-186

Ghost maging, based on single-pixel detection and multiple pattern illumination, is a crucial investigative tool in difficult-to-access wavelength regions. In the terahertz domain, where high-resolution imagers are mostly unavailable, ghost imaging is an optimal approach to embed the temporal dimension, creating a “hyperspectral” imager. In this framework, high resolution is mostly out of reach. Hence, it is particularly critical to developing practical approaches for microscopy. Here we experimentally demonstrate time-resolved nonlinear ghost imaging, a technique based on near-field, optical-to-terahertz nonlinear conversion and detection of illumination patterns. We show how space–time coupling affects near-field time-domain imaging, and we develop a complete methodology that overcomes fundamental systematic reconstruction issues. Our theoretical-experimental platform enables high-fidelity subwavelength imaging and carries relaxed constraints on the nonlinear generation crystal thickness. Our work establishes a rigorous framework to reconstruct hyperspectral images of complex samples inaccessible through standard fixed-time methods.

© 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Researchers combine lasers and terahertz waves in camera that sees 'unseen' detail

The time-resolved nonlinear ghost imaging camera uses a nonlinear crystal to convert standard laser light to terahertz patterns, allowing the reconstruction of complex samples using a single terahertz pixel. Credit: University of Sussex

https://phys.org/news/2020-02-combine-lasers-terahertz-camera-unseen.html


A team of physicists at the University of Sussex has successfully developed the first nonlinear camera capable of capturing high-resolution images of the interior of solid objects using terahertz (THz) radiation.

Led by Professor Marco Peccianti of the Emergent Photonics (EPic) Lab, Luana Olivieri, Dr. Juan S. Totero Gongora and a team of research students built a new type of THz camera capable of detecting THz electromagnetic waves with unprecedented accuracy.

Images produced using THz radiation are called 'hyperspectral' because the image consists of pixels, each one containing the electromagnetic signature of the object in that point.

Lying between microwaves and infrared in the electromagnetic spectrum, THz radiation easily penetrates materials like paper, clothes and plastic in the same way X-rays do, but without being harmful. It is safe to use with even the most delicate biological samples. THz imaging makes it possible to 'see' the molecular composition of objects and distinguish between different materials—such as sugar and cocaine, for example.

Explaining the significance of their achievement, Prof Peccianti said: "The core challenge in THz cameras is not about collecting an image, but it is about preserving the objects spectral fingerprint that can be easily corrupted by your technique. This is where the importance of our achievement lies. The fingerprint of all the details of the image is preserved in such a way that we can investigate the nature of the object in full detail. "

Artistic rendering of the terahertz field transmitted by an abstract object. Credit: University
of Sussex

 

Until now, cameras capable of capturing a hyperspectral image preserving all the fine details revealed by THz radiation had not been considered possible.

The EPic Lab team used a single-pixel camera to image sample objects with patterns of THz light. The prototype they built can detect how the object alters different patterns of THz light. By combining this information with the shape of each original pattern, the camera reveals the image of an object as well as its chemical composition.

Sources of THz radiation are very faint and hyperspectral imaging had, until now, limited fidelity. To overcome this, The Sussex team shone a standard laser onto a unique non-linear material capable of converting visible light to THz. The prototype camera creates THz electromagnetic waves very close to the sample, similar to how a microscope works. As THz waves can travel right through an object without affecting it, the resulting images reveal the shape and composition of objects in three dimensions.

Dr. Totero Gongora said: "This is a major step forward because we have demonstrated that all the possibilities explored in our previous theoretical research are not only feasible, but our camera works even better than we expected. While building our device, we discovered several ways to optimise the imaging process and now the technology is stable and works well. The next phase of our research will be in speeding up the image reconstruction process and taking us closer to applying THz cameras to real-world applications; like airport security, intelligent car sensors, quality control in manufacturing and even scanners to detect health problems like skin cancer."

Abstract-Super-resolved terahertz microscopy by knife-edge scan

V. Giliberti; M. Flammini; C. Ciano; E. Pontecorvo; E. Del Re; M. Ortolani

https://www.spiedigitallibrary.org/conference-proceedings-of-spie/10383/103830P/Super-resolved-terahertz-microscopy-by-knife-edge-scan/10.1117/12.2273796.short


We present a compact, all solid-state THz confocal microscope operating at 0.30 THz that achieves super-resolution by using the knife-edge scan approach. In the final reconstructed image, a lateral resolution of 60 μm ≈ λ/17 is demonstrated when the knife-edge is deep in the near-field of the sample surface. When the knife-edge is lifted up to λ/4 from the sample surface, a certain degree of super-resolution is maintained with a resolution of 0.4 mm, i.e. more than a factor 2 if compared to the diffraction-limited scheme. The present results open an interesting path towards super-resolved imaging with in-depth information that would be peculiar to THz microscopy systems.

© (2017) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.

University of New Mexico Spinout Aims to Develop Nanopore Sequencing Technology

Monica Heger

https://www.genomeweb.com/sequencing/university-new-mexico-spinout-aims-develop-nanopore-sequencing-technology

SAN FRANCISCO (GenomeWeb) – Armonica Technologies, a startup that has spun out of the University of New Mexico, is looking to develop nanopore sequencing technology that relies on stretching DNA through nanochannels that have a porous roof.

In August, the firm received $1.5 million in seed investment from New Mexico's Catalyst Fund.

The nanopore technology will be based on work from several UNM researchers: Steven Brueck, a professor of electrical and computer engineering at UNM's Center for High Technology Materials with an expertise in nanofabrication; Yuliya Kuznetsova, a research assistant professor whose expertise is in microscopy imaging techniques; Alexander Neumann, a postdoctoral fellow in the department of electrical and computer engineering; and Jeremy Edwards, a professor in the department of chemistry and chemical biology who focuses on sequencing technologies. Scott Goldman, associate principal of commercial effectiveness at Symphony Health Solutions, is president and CEO.

The design of the instrument will be based on porous nanochannels, which Brueck described in a 2008 study published in Nano Letters. The nanochannels, which have a porous roof that is made out of silica beads, enable DNA to be manipulated while it is captured inside. The enzyme lambda exonuclease is introduced through the roof of the nanochannel and converts double-stranded to single-stranded DNA, Brueck said. The channel also includes a barrier at one end, and after creating ssDNA, a voltage is applied to force the DNA through the porous roof.Brueck said that the goal is to commercialize the sequencing technology in around two years.

Brueck described the process as a piece of yarn threading its way through a stack of oranges. This "extended and convoluted" transport is actually an advantage, Brueck said, because it slows the DNA down.

A metal film and an insulator are built on top of the nanochannels with gaps that align with the nanochannel holes. Ultimately, Brueck said, some of the holes will have to be sealed, to keep the DNA molecules far enough apart from each other so that each is detected and read independently.

The insulator atop of the nanochannel will be just 1 nanometer thick, Brueck said, to give spatial resolution. To detect individual bases, the firm plans to use surface-enhanced coherent anti-Stokes Raman scattering (SECARS), a vibrational imaging technique that takes advantage of the fact that each nucleotide has a unique vibrational frequency. Cameras then capture the DNA moving through the pores.

The detection piece is the biggest remaining challenge, Brueck said. Surface enhancement of the insulator improves the sensitivity of detection, he said, but "whether we can get down to single-molecule detection remains to be proven."

In the Nano Letters study, Brueck's team demonstrated that the nanochannel constructs could be built and that DNA would go through them. In that study, they tested lambda phage DNA that had been fluorescently stained. The DNA was 48.5 kilobase pairs long, which is the read length the firm is targeting initially.

In addition, In 2013, Brueck's team published a study in IEEE, to show that Terahertz microscopy could detect absorption signatures of DNA in the nanochannel chips, which helped lay the initial groundwork for detection, but "terahertz microscopy cannot resolve individual bases," he said. The researchers are now working on developing the SECARS-based detection technique, but have so far not yet demonstrated it on the single-molecule level or coupled it with the nanochannel constructs.

The initial platform will be a large laboratory instrument that uses lasers and a microscope for detection, Brueck said, but the ultimate goal is to shrink that down to a handheld device.

Brueck said that the next step is to refine the process of moving the DNA through the nanochannels and up through the porous roof and metal insulator — to quantify the translocation and figure out the exact configuration of the pores. After that, he said, the company will tackle the detection process.

Armonica has discussed both developing a device on which it would offer services as well as commercializing a platform. Which model it ends up pursuing will "depend on how robust we can make the device," Brueck said.

One advantage of the technology is that sample prep will be minimal — all that will be required is an initial DNA purification step, as well as some fragmentation to generate the long DNA fragments. Brueck said that although 50 kilobases is the starting point for read lengths, the team does not yet know whether that's the limit.

In terms of applications, Brueck said that the company is targeting a sequencing instrument that reads individual bases, but if it identifies intermediate applications with commercial potential, it would pursue those.

Terahertz microscopy breakthrough revealed

Image: nanostructured optical materials boost photonic device efficiencies for THz microscopy
By: Rebecca Pool
http://www.microscopy-analysis.com/editorials/editorial-listings/terahertz-microscopy-breakthrough-revealed

Researchers from University College London, UK, and Sandia National Laboratories, US, have demonstrated optoelectronic probes for high spatial resolution terahertz microscopy.

 

Similar to infra-red waves and x-rays, terahertz waves allow observing objects and phenomena invisible to the human eye, but the clarity of THz images is limited by diffraction.

 

To advance resolution capabilities of near-field scanning probe microscopy with terahertz waves, Dr Mitrofanov and colleagues have developed a nanostructured terahertz detector and integrated it into the near-field microscopy probe.

 

The detector structure contains an array of optical nanoantennas and a distributed Bragg reflector.

 

When illuminated by a short optical pulse, this structure traps optical photons and activates a small terahertz detector, which allows sampling terahertz waves on the scale over 100 times smaller than the terahertz wavelength.

 

The researches anticipate that applications of these probes with terahertz time-domain spectroscopy will enable further scientific investigations of terahertz phenomena.

 

The technique of near-field scanning probe microscopy was pioneered using radio waves by Professor Sir Eric Ash in the Department of Electronic and Electrical Engineering at UCL, more than 40 years ago. This technique opened doors to investigations of sub-wavelength scale objects.

 

Research is published in ACS Photonics.