Abstract-Observation of the Terahertz Pulse Shaping Due to Intensity-Induced Additional Phase in Two-Color Filaments

 

Chen Gong, Takahiro Teramoto, Masayoshi Tonouchi, 

https://link.springer.com/article/10.1007/s10762-021-00797-4

As a promising terahertz (THz) source, two-color laser filamentation in gases attracts an exponential growth of interest because of the scalability of output THz pulse energy and bandwidth with input parameters. However, nonlinear effects within the laser filament on the THz pulse generation process, such as intensity-dependent refractive index change induced additional phase, have never been studied in depth. In this paper, we experimentally investigate the THz waveform evolution with input infrared pump energy from 1.75 ~ 2.75 mJ were recorded by an air biased coherent detection (ABCD) sampling setup. We observe that the magnitude ratio of the positive and negative peaks increases with the pump pulse energy, and the smooth peak at the tail gradually disappears. Based on the photocurrent model, our calculation shows that the modulation is caused by the plasma-induced additional phase that varies with incident laser intensity. Additionally, the smooth peak at the tail is considered to be caused by the fading of the residual current after the negative peak.

Abstract-Label-Free Observation of Micrometric Inhomogeneity of Human Breast Cancer Cell Density Using Terahertz Near-Field Microscopy

 

Kosuke Okada, Quentin Cassar, Hironaru Murakami, Gaëtan MacGrogan , Jean-Paul Guillet, Patrick Mounaix, Masayoshi Tonouchi, Kazunori Serita

https://www.mdpi.com/2304-6732/8/5/151

Terahertz-light imaging is attracting great attention as a new approach in non-invasive/non-staining biopsy of cancerous tissues. Positively, terahertz light has been shown to be sensitive to the cell density, the hydration content, and the chemical composition of biological samples. However, the spatial resolution of terahertz imaging is typically limited to several millimeters, making it difficult to apply the technology to image biological tissues which have sub-terahertz-wavelength-scale inhomogeneity. For overcoming the resolution, we have recently developed a terahertz near-field microscope with a spatial resolution of 10 µm, named scanning point terahertz source (SPoTS) microscope. In contrast to conventional far-field terahertz techniques, this microscope features the near-field interactions between samples and point terahertz sources on a sub-terahertz-wavelength scale. Herein, to evaluate the usefulness of terahertz imaging in cancer tissue biopsy in greater detail, we performed terahertz near-field imaging of a paraffin-embedded human-breast-cancer section having sub-terahertz-wavelength-scale inhomogeneity of the cancer cell density using the SPoTS microscope. The observed terahertz images successfully visualized local (~250 µm) inhomogeneities of the cell density in breast invasive ductal carcinoma. These results may bypass the terahertz limitation in terms of spatial resolution and may further motivate the application of terahertz light to cancer tissue biopsy.

Abstract-Simplified formulas for the generation of terahertz waves from semiconductor surfaces excited with a femtosecond laser

Masayoshi Tonouchi

https://arxiv.org/abs/2005.07878

We derive simple formulas to explain terahertz (THz) emission from semiconductor surfaces excited by a femtosecond (fs) laser. Femtosecond optical pulses with energies larger than the bandgap create photocarriers which travel and generate THz radiation, according to the time derivative of the photocurrent. By assuming that only electrons traveling in an ultrafast time scale, less than a few hundred fs, contribute to THz radiation, one can obtain simple expressions for the emission originating from the photocarrier drift accelerated with a built-in field or from the photocarrier diffusion. The emission amplitude of the former is in proportion with electron mobility, the Schottky-Barrier height, and the laser intensity and one of the latter with the laser intensity and diffusion coefficient squared. We also discuss the formula for emission from metal-insulator-semiconductor structures. The derived expressions are useful in understanding the THz emission properties observed by a laser THz emission microscope (LTEM), bringing LTEM into real applications in the field of semiconductor research and development.

Abstract-Terahertz Excitonics in Carbon Nanotubes: Exciton Autoionization and Multiplication

Filchito Bagsican, Michael Wais, Natsumi Komatsu, Weilu Gao, Weilu Gao, Lincoln W. Weber, Kazunori Serita,  Hironaru Murakami, Karsten. Held, Frank A. Hegmann, Masayoshi Tonouchi, Junichiro Kono, Iwao Kawaya, Marco Battiato

https://pubs.acs.org/doi/10.1021/acs.nanolett.9b05082

Excitons play major roles in optical processes in modern semiconductors, such as single-wall carbon nanotubes (CNTs), transition metal dichalcogenides, and 2D perovskite quantum wells. They possess extremely large binding energies (>100 meV), dominating absorption and emission spectra even at high temperatures. The large binding energies imply that they are stable, that is, hard to ionize, rendering them seemingly unsuited for optoelectronic devices that require mobile charge carriers, especially terahertz emitters and solar cells. Here, we have conducted terahertz emission and photocurrent studies on films of aligned single-chirality semiconducting CNTs and find that excitons autoionize, i.e., spontaneously dissociate into electrons and holes. This process naturally occurs ultrafast (<1 ps) while conserving energy and momentum. The created carriers can then be accelerated to emit a burst of terahertz radiation when a dc bias is applied, with promising efficiency in comparison to standard GaAs-based emitters. Furthermore, at high bias, the accelerated carriers acquire high enough kinetic energy to create secondary excitons through impact exciton generation, again in a fully energy and momentum conserving fashion. This exciton multiplication process leads to a nonlinear photocurrent increase as a function of bias. Our theoretical simulations based on nonequilibrium Boltzmann transport equations, taking into account all possible scattering pathways and a realistic band structure, reproduce all of our experimental data semiquantitatively. These results not only elucidate the momentum-dependent ultrafast dynamics of excitons and carriers in CNTs but also suggest promising routes toward terahertz excitonics despite the orders-of-magnitude mismatch between the exciton binding energies and the terahertz photon energies.

Abstract-A Terahertz-Microfluidic Chip with a Few Arrays of Asymmetric Meta-Atoms for the Ultra-Trace Sensing of Solutions

Kazunori Serita,  Hironaru Murakami, Iwao Kawayama, Masayoshi Tonouchi

https://www.mdpi.com/2304-6732/6/1/12/htm

Biosensing with terahertz (THz) waves has received large amounts of attention due to its potential to detect the functional expression of biomolecules in a label-free fashion. However, many practical challenges against the diffraction limit of THz waves and the strong absorption of THz waves into polar solvents still remain in the development of compact biosensors. Here, we present a non-linear, optical, crystal-based THz-microfluidic chip with a few arrays of asymmetric meta-atoms, an elementary unit of metamaterials, for the measurement of trace amounts of solution samples. A near-field THz emission source, that is locally generated in the process of optical rectification at a fs (femtosecond) laser irradiation spot, induces a sharp Fano resonance and modifies the resonance frequency of the meta-atoms when the channel is filled with solution samples of different concentrations. Using this chip, we successfully detected minute changes in the concentration of trace amounts of mineral water and aqueous sugar solutions by monitoring the shift in the resonance frequency. A higher detectable sensitivity of 1.4 fmol of solute in a 128 pL volume of solution was achieved. This was an improvement of one order of magnitude in the sensitivity compared to our previous experiment.

Abstract-Plasmon-induced transparency in metamaterials: Active near field coupling between bright superconducting and dark metallic mode resonators

Applied Physics Letters

Wei Cao, Ranjan Singh,  Caihong Zhang, Jiaguang Han,  Masayoshi Tonouchi, Weili Zhang

https://aip.scitation.org/doi/abs/10.1063/1.4819389

Structured plasmonic metamaterial devices offer the design flexibility to be size scaled for operation across the electromagnetic spectrum and are extremely attractive for generating electromagnetically induced transparency and slow-light behaviors via coupling of bright and dark subwavelength resonators. Here, we experimentally demonstrate a thermally active superconductor-metal coupled resonator based hybrid terahertz metamaterial on a sapphire substrate that shows tunable transparency and slow light behavior as the metamaterial chip is cooled below the high-temperature superconducting phase transition temperature. This hybrid metamaterial opens up the avenues for designing micro-sized active circuitry with switching, modulation, and “slowing down terahertz light” capabilities.

Abstract-Reflection type scanning laser terahertz near-field spectroscopy and imaging system for bio-applications

Kosuke Okada, Kazunori Serita, Iwao Kawayama, Hironaru Murakami, and Masayoshi Tonouchi

https://www.osapublishing.org/abstract.cfm?URI=cleo_si-2018-SW3D.4

We developed a reflection type scanning laser THz near-field spectroscopy and imaging system and evaluated its basic performance. We found that this system has huge potential for high-resolution, high-sensitive and high-speed biological measurements.

© 2018 The Author(s)

Sensing Method Could Detect Cancer & Diabetes Earlier

https://www.azosensors.com/news.aspx?newsID=12364

By Louise SaulFeb 27 2018

Scientists at Osaka University have developed a new sensing method, which has the potential to detect both cancer and diabetes earlier than ever possible before.

The use of terahertz (THz) waves for biosensing is currently of great interest to scientists and is receiving considerable attention. The team in Osaka have developed a THz microfluidic chip with arrays of meta-atoms that can be used for microanalysis. It is highly sensitive, and label-free, for measurements of biological samples. The new chip can detect trace amounts of known materials and minimal changes in optical constants. The research was published in APL Photonics.

THz radiation lies in between infrared and microwave radiation. The terahertz region provides essential information that clarifies biological reaction dynamics, including the hydrogen bonds and hydrophobic interactions, and it is at comparatively lower energy than that of infrared absorption. They can detect molecular vibrations and rotations, without using labels that can affect the properties of the substances of interest.

Microfluidic devices only need a very low sample volume for measurements, so they are seen as very promising analytical systems. The group from Osaka University have now developed a nonlinear optical crystal (NLOC) chip, combining the THz waves with a microfluidic device, meaning that the proximity of the THz wave source and the solution of interest in a microchannel can be combined.

The early and rapid detection of common diseases is set to be a major application of the technique. There is the potential that cancer, diabetes, and even the influenza virus would be able to be detected with very small volumes of bodily fluid. The sample volume needed allows for the patients to have their pain and discomfort from exploratory procedures reduced. The new technique also has another major benefit of allowing living cells to be analyzed in a non-destructive way.

The technique has been limited previously due to the diffraction limit of THz waves and their strong absorption by water. The new research has shown that THz time-domain spectroscopy (THz-TDS) is a technique that can give new insights into the functional expression and structural change of water, biopolymers, and DNA. When THz methods can be combined with microfluidic devices, it allows for the development of compact THz sensors, as well as new analytical THz devices that have a higher sensitivity.

Using our technique, we have been able to detect solution concentrations of several femtomoles in volumes of less than a nanoliter. Such high-sensitivity detection without the need for labeling moieties has great potential for future low-invasivity clinical techniques.

Professor Masayoshi Tonouchi, Professor of the Tonouchi lab at Osaka University

The sensor chip compared frequency shifts resulting from the presence of ions to those of pure water to analyze mineral concentrations. The chip was tested by using both distilled water and commercial mineral water, and when observing the amount of shift from the resonance frequency of pure water, they found that the solute can be detected with a sensitivity of up to 31.8 femtomoles. The sensitivity of the technique is comparable to standard fluorescence systems, but it can be improved by further optimization of the structure and the arrangement of meta-atoms. Altering the channel depth to reduce the THz absorption into the water can also optimize results.

Achieving high sensitivity without the need for a high-power optical or THz source, near-field probes or prisms opens up a number of possibilities.

Kazunori Serita, Co-Author

Serita explains how their potential findings could lead to rapid detection and compact device designs. He believes the results will lead to an acceleration in the development of THz lab-on-a-chip devices. The new adaptable technology has the potential to have a wide range of uses across many areas, including biochemistry, analytical chemistry, cell biology, and clinical medicine. The low cost of NLOC chips would also allow for disposable and compact sensors, which would be highly beneficial to both fields of medicine and biology.

Thumbnail Image Credit: GiroScience/Shutterstock

Disclaimer: The views expressed here are those of the author expressed in their private capacity and do not necessarily represent the views of AZoM.com Limited T/A AZoNetwork the owner and operator of this website. This disclaimer forms part of the Terms and conditions of use of this website.

Microanalysis of biological samples for early disease detection

A schematic drawing of solution measurement by using fabricated terahertz microfluidic chip. The chip consists of a local THz radiation point source, a single microchannel and a few arrays of split ring resonators. The THz waves are generated by irradiating laser beam from the backside of the crystal and efficiently interact with the solution flowing inside the microchannel. The optical microscope image of fabricated microfluidic chip is also shown.

Credit: Osaka University

https://www.sciencedaily.com/releases/2018/02/180219103211.htm

The use of terahertz (THz) waves for biosensing is currently receiving considerable attention. THz waves are able to detect molecular vibrations and rotations, without using labels that can affect the properties of the substances of interest.

However, until now, the diffraction limit of THz waves and their strong absorption by water have constrained this technique.

Microfluidic devices are also promising analytical systems because of the low sample volumes needed for sample measurement.

A group of researchers from Osaka University has now developed a nonlinear optical crystal (NLOC) chip, which combines THz waves with a microfluidic device, utilizing the close proximity of the THz wave source and the solution of interest in a microchannel. Their work was published in APL Photonics.

"Using our technique, we have been able to detect solution concentrations of several femtomoles in volumes of less than a nanoliter," corresponding author Masayoshi Tonouchi says. "Such high-sensitivity detection without the need for labelling moieties has great potential for future low-invasivity clinical techniques."

Early and rapid detection of a number of common diseases is expected to be one of the major applications of the technique. Cancer, diabetes, and the influenza virus could potentially be detected with only very small volumes of bodily fluid, reducing the pain and discomfort of numerous exploratory procedures for patients. In addition, the technique allows living cells to be analyzed in a non-destructive way, which has numerous potential benefits in research.

The developed NLOC chip is able to locally generate the THz radiation in close proximity to the single microchannel device, improving efficiency. The sensor chip was used to analyze mineral concentrations by comparing frequency shifts resulting from the presence of ions to those of pure water. Using this technique they determined a sensitivity of 31.8 femtomoles.

"Achieving high sensitivity without the need for a high-power optical or THz source, near-field probes or prisms, opens up a number of possibilities," lead author Kazunori Serita says. "We are very excited about the potential of our findings to lead to rapid detection and compact device design. In particular, we see our results accelerating the development of THz lab-on-a-chip devices."

This highly adaptable technology is likely to ripple out into many areas of analytical and biochemistry, as well as cell biology, and clinical medicine.

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Story Source:

Materials provided by Osaka University. Note: Content may be edited for style and length.

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Journal Reference:

1. Kazunori Serita, Eiki Matsuda, Kosuke Okada, Hironaru Murakami, Iwao Kawayama, Masayoshi Tonouchi. Invited Article: Terahertz microfluidic chips sensitivity-enhanced with a few arrays of meta-atoms. APL Photonics, 2018; 3 (5): 051603 DOI: 10.1063/1.5007681

Abstract-Invited Article: Terahertz microfluidic chips sensitivity-enhanced with a few arrays of meta-atoms

Kazunori Serita, Eiki Matsuda, Kosuke Okada, Hironaru Murakami, Iwao Kawayama, Masayoshi Tonouchi,

http://aip.scitation.org/doi/abs/10.1063/1.5007681

We present a nonlinear optical crystal (NLOC)-based terahertz (THz) microfluidic chip with a few arrays of split ring resonators (SRRs) for ultra-trace and quantitative measurements of liquid solutions. The proposed chip operates on the basis of near-field coupling between the SRRs and a local emission of point like THz source that is generated in the process of optical rectification in NLOCs on a sub-wavelength scale. The liquid solutions flowing inside the microchannel modify the resonance frequency and peak attenuation in the THz transmission spectra. In contrast to conventional bio-sensing with far/near-field THz waves, our technique can be expected to compactify the chip design as well as realize high sensitive near-field measurement of liquid solutions without any high-power optical/THz source, near-field probes, and prisms. Using this chip, we have succeeded in observing the 31.8 fmol of ion concentration in actual amount of 318 pl water solutions from the shift of the resonance frequency. The technique opens the door to microanalysis of biological samples with THz waves and accelerates development of THz lab-on-chip devices.

Abstract-Imaging Polarization in GaN Surfaces by Laser Terahertz Emission Microscopy

Yuji Sakai, Iwao Kawayama, Hidetoshi Nakanishi, and Masayoshi Tonouchi

https://www.osapublishing.org/abstract.cfm?uri=cleo_si-2017-SM4J.6&origin=search

Polarizations in GaN surfaces are visualized using terahertz emission microscopy. A non-radiative-inversion domain that is hardly distinguishable with photoluminescence imaging was clearly observed with this method.

© 2017 OSA

Abstract-Measurable lower limit of thin film conductivity with parallel plate waveguide terahertz time domain spectroscopy

Manjakavahoaka Razanoelina, Shohei Ohashi, Iwao Kawayama, Hironaru Murakami, Annick F. Dégardin, Alain J. Kreisler, and Masayoshi Tonouchi

https://www.osapublishing.org/ol/abstract.cfm?uri=ol-42-15-3056&origin=search

Parallel plate waveguide (PPWG) terahertz (THz) time domain spectroscopy (TDS) is a powerful tool to investigate the properties of thin and low conductive materials. In this Letter, we determine the lower limit of detection of the PPWG–THz–TDS approach. We provide a closed-form expression of the minimal measurable conductivity by the system. The experimental results of amorphous YBa2Cu3O7−𝛿${\mathrm{YBa}}_2{\mathrm{Cu}}_3{\mathrm{O}}_{7-\delta }$ films indicate that the factor limiting the spectroscopic modality is the waveguide device misalignment. On the other hand, the expression of the minimal detectable conductivity provides a clear scheme of optimization by increasing the waveguide length and therefore enhancing the sensitivity of the system.

© 2017 Optical Society of America

Abstract-High Efficient Terahertz Generation Using Tilted-Pulse-Front Photoexcitation of Semiconductor Surface

Yuri Avetisyan, Armen Makaryan, and Masayoshi Tonouchi

https://www.osapublishing.org/abstract.cfm?uri=cleo_at-2017-JW2A.109&origin=search

It is shown that photoexcitation of InAs surface with tilted-front laser pulses allows controlling the direction of terahertz emission and by that way achieving significant increase in the generated power.

© 2017 OSA

Abstract-Probing low-density carriers in a single atomic layer using terahertz parallel-plate waveguides

Manjakavahoaka. Razanoelina, Filchito Renee Bagsican, Iwao Kawayama, Xiang Zhang, Lulu Ma, Hironaru Murakami, Robert Vajtai, Pulickel M. Ajayan, Junichiro Kono, Masayoshi Tonouchi, 

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-24-4-3885

As novel classes of two-dimensional (2D) materials and heterostructures continue to emerge at an increasing pace, methods are being sought for elucidating their electronic properties rapidly, non-destructively, and sensitively. Terahertz (THz) time-domain spectroscopy is a well-established method for characterizing charge carriers in a contactless fashion, but its sensitivity is limited, making it a challenge to study atomically thin materials, which often have low conductivities. Here, we employ THz parallel-plate waveguides to study monolayer graphene with low carrier densities. We demonstrate that a carrier density of ~2 × 1011 cm−2, which induces less than 1% absorption in conventional THz transmission spectroscopy, exhibits ~30% absorption in our waveguide geometry. The amount of absorption exponentially increases with both the sheet conductivity and the waveguide length. Therefore, the minimum detectable conductivity of this method sensitively increases by simply increasing the length of the waveguide along which the THz wave propagates. In turn, enabling the detection of low-conductivity carriers in a straightforward, macroscopic configuration that is compatible with any standard time-domain THz spectroscopy setup. These results are promising for further studies of charge carriers in a diverse range of emerging 2D materials.

© 2016 Optical Society of America

Full Article  |  PDF Article

Focus on Superconductor Terahertz Science and Applications

Focus on Superconductor Terahertz Science and Applications

http://iopscience.iop.org/0953-2048/focus/Focus-on-Superconductor-Terahertz-Science-and-Applications

Guest Editors

Masayoshi Tonouchi, Osaka University, Japan Boris S Karasik, Jet Propulsion Laboratory, USA Michael Siegel, Karlsruhe Institute of Technology, Germany Jian Chen, Nanjing University, China

Scope

SUST invites manuscripts that document the state-of-the-art in superconductor terahertz science and applications. Terahertz technology in the frequency range 0.3–30 THz has attracted much interest owing to potential applications in many fields for astronomy, medical diagnostics and biology, quantum communications, security, defense, non-destructive testing, and so on. Terahertz frequency range lies in between microwave and optical ranges, and shares some characteristics of both regimes. The nature of terahertz waves that bridges electronics and photonics has made the terahertz science and technology an important area of research. Terahertz devices with better performance, such as e.g. narrow-band high-brightness sources, or highly-sensitive broad-band detectors are now available. Terahertz technology is presently employed in space science to explore the universe, as well as for many terrestrial applications.

Our special issue aims at highlighting all developments in the broad area of superconductor THz science and applications. We will consider theoretical, numerical, and experimental papers that cover but are not limited to the following topics:

• Novel THz sources and detectors
• THz imaging and spectroscopy techniques and systems
• New THz materials and devices
• New phenomena in superconductors probed by THz waves
• Nonlinear THz interactions with superconductors
• Development of THz devices, components, and systems
• Applications of THz radiation in astronomy, physics, life sciences, and industries 

How to submit

Either go to add or click on 'Submit an article' on the right hand side of this page, and select 'Special Issue Article' as the article type, then 'Superconductor Terahertz Science and Applications'.

Important dates and deadlines

Submission deadline 1 August 2016.
Approximate online publication January 2017. 

More information about Superconductor Science and Technology can be found on our website: www.iopscience.org/sust

Abstract-Comparison between laser terahertz emission microscope and conventional methods for analysis of polycrystalline silicon solar cell

Hidetoshi Nakanishi^1,a), Akira Ito^1,b), Kazuhisa Takayama^2,c), Iwao Kawayama^2,d), Hironaru Murakami^2,e) and Masayoshi Tonouchi^2,f)
http://scitation.aip.org/content/aip/journal/adva/5/11/10.1063/1.4935913?TRACK=RSS
a) nakanisi@screen.co.jp, Tel:+81-75-931-7925(ext.8303427). 322 Furukawa-cho, Hazukashi, Fushimi-ku, Kyoto 612-8486, Japan
b) a.ito@screen.co.jp, Tel:+81-75-931-7925(ext.8306049)
c) takayama.k0123@gmail.com, Tel:+81-6-6879-7983
d) kawayama@ile.osaka-u.ac.jp, Tel:+81-6-6879-7983. 2-6 Yamadaoka, Suita, Osaka 565-0871, Japan
e) hiro@ile.osaka-u.ac.jp, Tel:+81-6-6879-7982
f) tonouchi@ile.osaka-u.ac.jp, Tel:+81-6-6879-7981.
AIP Advances 5, 117129 (2015); http://dx.doi.org/10.1063/1.4935913

A laser terahertz emission microscope (LTEM) can be used for noncontact inspection to detect the waveforms of photoinduced terahertz emissions from material devices. In this study, we experimentally compared the performance of LTEM with conventional analysis methods, e.g.,electroluminescence (EL), photoluminescence (PL), and laser beam induced current (LBIC), as an inspection method for solar cells. The results showed that LTEM was more sensitive to the characteristics of the depletion layer of the polycrystalline solar cell compared with EL, PL,and LBIC and that it could be used as a complementary tool to the conventional analysis methods for a solar cell