Abstract-Excitation of multiple phonon modes in copper metaborate CuB 2 O 4 via nonresonant impulsive stimulated Raman scattering

Kotaro Imasaka, Roman V. Pisarev, Leonard N. Bezmaternykh, Tsutomu Shimura, Alexandra M. Kalashnikova, and Takuya Satoh

https://journals.aps.org/prb/accepted/62070Od9Oae1523411b61fc481644a9591593bae3

The excitation of four coherent phonon modes of different symmetries are realized in copper metaborate CuB${}_2$O${}_4$ via impulsive stimulated Raman scattering (ISRS). The phonons are detected by monitoring changes in the linear optical birefringence using the polarimetric detection (PD) technique. We compare the results of the ISRS-PD experiment to the polarized spontaneous Raman scattering spectra. We show that agreement between the two sets of data obtained by these allied techniques in a wide phonon frequency range of 4--14\,THz can be achieved by taking into account the symmetry of the phonon modes and corresponding excitation and detection selection rules. It is also important to account for the difference between incoherent and coherent phonons in terms of their contributions to the Raman scattering process. This comparative analysis highlights the importance of the ratio between the frequency of a particular mode, and the pump and probe spectral widths. We analytically demonstrate that the pump and probe pulse durations of 90 and 50 fs, respectively, used in our experiments limit the highest frequency of the excited and detected coherent phonon modes to 12 THz, and define their relative amplitudes.

Abstract-Narrowband terahertz radiation by impulsive stimulated Raman scattering in an above-room-temperature organic ferroelectric benzimidazole

M. Sotome, N. Kida, S. Horiuchi, and H. Okamoto

https://journals.aps.org/pra/accepted/5307fYe8D141d06616b992a17369297dd547b7888

In noncentrosymmetric media, optical rectification is known to be a general mechanism of the generation of terahertz electromagnetic waves. Here, we show that effective terahertz radiation is possible via a different mechanism in a hydrogen-bonded organic molecular ferroelectric 5,6-dichloro-2-methylbenzimidazole (DCMBI). By the irradiation of a femtosecond laser pulse on a single crystal of DCMBI at room temperature, we observe a strong terahertz radiation. The emitted terahertz wave consists of three oscillatory components, the frequencies of which agree with those of Raman- and infrared-active phonon modes. This suggests that the terahertz radiation is attributed to polarization modulations by infrared-active phonons excited via impulsive stimulated Raman scattering processes. By taking into account the Raman polarizability tensor and dipole-moment for each phonon, we succeeded in reproducing not only the spectrum of the terahertz radiation, but also its time characteristic. The analysis method is discussed in detail. Our result provides a new way for the light-induced terahertz radiation in organic ferroelectrics. {I.

Abstract-Anharmonic phonon-polariton dynamics in ferroelectric LiNbO 3 studied with single-shot pump-probe imaging spectroscopy

T. Kuribayashi, T. Motoyama, Y. Arashida, J. Takeda,

https://www.researchgate.net/publication/325007933_Anharmonic_phonon-polariton_dynamics_in_ferroelectric_LiNbO_3_studied_with_single-shot_pump-probe_imaging_spectroscopy

We demonstrate that single-shot pump-probe imaging spectroscopy with an echelon mirror enables us to disclose the ferroelectric phonon-polariton dynamics across a wide temperature range from 10 K to 375 K while avoiding the photorefractive effects that appear prominently at low temperatures. The E-mode phonon-polaritons corresponding to the two transverse optical modes, TO1 and TO3, up to ∼7 THz were induced in LiNbO3 through an impulsive stimulated Raman scattering process. Subsequently, using single-shot pump-probe imaging spectroscopy over a minimal cumulative time, we successfully visualized the phonon-polariton dynamics in time-wavelength space even at low temperatures. We found that the phase-matching condition significantly affected the observed temperature-dependent phonon-polariton frequency shift. The anharmonicity of the TO1 and TO3 modes was then evaluated based on an anharmonic model involving higher-order interactions with acoustic phonons while eliminating the influence of the frequency shift due to the phase-matching condition. The observed wavenumber-dependent damping rate was analyzed by considering the bilinear coupling of the TO1 or TO3 modes with the thermally activated relaxation mode. We found that the phonon-polariton with a higher frequency and wavenumber had a higher damping rate at high temperatures because of its frequent interaction with the thermally activated relaxation mode and acoustic phonons. The TO3 mode displayed greater bilinear coupling than the TO1 mode, which may also have contributed to the observed high damping rate. Thus, using our unique single-shot spectroscopy technique, we could reveal the overall anharmonic characteristics of the E-mode phonon-polaritons arising from both the acoustic phonons and the relaxation mode.

Abstract-Impulsive Raman spectroscopy via precision measurement of frequency shift with low energy excitation

Dekel Raanan, Liqing Ren, Dan Oron, and Yaron Silberberg

https://www.osapublishing.org/ol/abstract.cfm?uri=ol-43-3-470&origin=search

Stimulated Raman scattering (SRS) has recently become useful for chemically selective bioimaging. It is usually measured via modulation transfer from the pump beam to the Stokes beam. Impulsive stimulated Raman spectroscopy, on the other hand, relies on the spectral shift of ultrashort pulses as they propagate in a Raman active sample. This method was considered impractical with low energy pulses since the observed shifts are very small compared to the excitation pulse bandwidth, spanning many terahertz. Here we present a new apparatus, using tools borrowed from the field of precision measurement, for the detection of low-frequency Raman lines via stimulated-Raman-scattering-induced spectral shifts. This method does not require any spectral filtration and is therefore an excellent candidate to resolve low-lying Raman lines (

<200  cm−1$<200{\mathrm{cm}}^{-1}$), which are commonly masked by the strong Rayleigh scattering peak. Having the advantage of the high repetition rate of the ultrafast oscillator, we reduce the noise level by implementing a lock-in detection scheme with a wavelength shift sensitivity well below 100 fm. This is demonstrated by the measurement of low-frequency Raman lines of various liquid samples.

© 2018 Optical Society of America

Abstract-Terahertz Sum-Frequency Excitation of a Raman-Active Phonon

Sebastian Maehrlein, Alexander Paarmann, Martin Wolf, and Tobias Kampfrath

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.119.127402

In stimulated Raman scattering, two incident optical waves induce a force oscillating at the difference of the two light frequencies. This process has enabled important applications such as the excitation and coherent control of phonons and magnons by femtosecond laser pulses. Here, we experimentally and theoretically demonstrate the so far neglected up-conversion counterpart of this process: THz sum-frequency excitation of a Raman-active phonon mode, which is tantamount to two-photon absorption by an optical transition between two adjacent vibrational levels. Coherent control of an optical lattice vibration of diamond is achieved by an intense terahertz pulse whose spectrum is centered at half the phonon frequency of 40 THz. Remarkably, the carrier-envelope phase of the THz pulse is directly transferred into the phase of the lattice vibration. New prospects in general infrared spectroscopy, action spectroscopy, and lattice trajectory control in the electronic ground state emerge.

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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.

Abstract-Creation of twisted terahertz carrying orbital angular momentum via stimulated Raman scattering in a plasma vortex

H Sobhani

http://iopscience.iop.org/article/10.1088/1555-6611/aa7f04/pdf

Here, a scheme for the generation of twisted terahertz radiation in a plasma vortex with a helical structure is proposed. Based on stimulated Raman scattering, the incident laser decays into the Langmuir wave. Beating the Langmuir wave with the plasma wave of the media causes the production of current density. The current density can excite twisted radiation at the terahertz frequency. For an incident laser with Gaussian envelops, the orbital angular momentum of terahertz radiation is provoked by the helicity of the plasma vortex. Furthermore, for the Laguerre–Gaussian laser, the orbital angular momentum of terahertz radiation is equal to the difference between the topological charge of the lasers and the electron plasma vortex.

Abstract-Longitudinal Optical Phonon-Plasmon Coupled Mode in Undoped GaAs/n-Type GaAs Epitaxial Structures Observed by Raman Scattering and Terahertz Time-Domain Spectroscopic Measurements: Difference in Observed Modes and Initial Polarization Effects

Hideo Takeuchi,   Takahiro Sumioka,   Masaaki Nakayama,

http://ieeexplore.ieee.org/document/7829414/

We investigated longitudinal optical (LO) phonon-plasmon coupled (LOPC) mode in undoped GaAs/n -type GaAs epitaxial structures using Raman scattering and terahertz time-domain spectroscopic measurements. In the Raman measurement, the LOPC mode, the frequency of which is determined by the doped electron density in the n -type layer, was observed in addition to the LO phonon in the undoped layer. Contrastingly, in terahertz time-domain measurements, the frequency of the observed coherent LOPC mode is dominated by a photogenerated electron density: frequency-tunable LOPC mode. This indicates that the LOPC mode is generated in the undoped layer. Thus, the probing mechanisms for the LOPC mode are different in the Raman and terahertz time-domain measurements. The built-in electric field exists in the undoped layer. This field enlarges the initial polarization of the LO phonon and, as a result, enables to observe the coherent LOPC mode generated in the undoped layer with the use of the terahertz time-domain spectroscopy.

Abstract-Terahertz radiation induced by coherent phonon generation via impulsive stimulated Raman scattering in paratellurite

M. Sotome, N. Kida, R. Takeda, and H. Okamoto
https://journals.aps.org/pra/abstract/10.1103/PhysRevA.90.033842

We report on the observation of terahertz radiation in a noncentrosymmetric insulating oxide, paratellurite (α−TeO2), by irradiation of a femtosecond laser pulse at room temperature. In the power spectrum of the terahertz radiation, an intensity fringe pattern with a period of ∼0.25 THz shows up below 3 THz. It can be reproduced by taking into account the effective generation length for the terahertz radiation with a poor phase-matching condition. In addition, a temporal oscillation component appears in the radiated terahertz wave with a frequency of ∼3.71 THz, which is in good agreement with the center frequency of the Raman active longitudinal optical E mode. On the basis of comprehensive polarized optical and Raman spectroscopic studies, we explain the generation mechanism of the temporal oscillation component in terms of the coherent phonon generation via impulsive stimulated Raman scattering.

DOI: http://dx.doi.org/10.1103/PhysRevA.90.033842

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OT- Raman scattering key to next-gen laser optical comms

http://global.ofweek.com/news/Raman-scattering-key-to-next-gen-laser-optical-comms-13900

The improvements in the performance of powerful lasers, optical fibres and peripheral technology have provided a sizable contribution to the proliferation of global telecommunications based on the transmission of 10GHz pulses of light. Particularly, the three most important properties of lasers for telecommunications are high power, single frequency and ultra-short pulse width.

Innovations pertaining to this technology can be found in the research being conducted by Professor Masayuki Katsuragawa, at the department of applied physics and chemistry, UEC.

"My research is focused on the manipulation of light-matter interaction for producing ultra-short pulses of laser light," stated Katsuragawa. "Our recent experiments on adiabatic stimulated Raman scattering in parahydrogen show potential for the realisation of laser light sources producing pulses at terahertz repetition-rate frequencies. These ultra-short pulses offer a new 'axis' in the evolution of laser based optical science."

Here, the 'axis' refers to ultrahigh-repetition-rate trains of monocycle pulses with precise control of the phase of the laser light pulses. Recently, Katsuragawa and his colleagues have reported on the realisation of ultrashort pulse trains of 1.8fs in duration and repetition frequency of 125THz by stimulated Raman scattering (SRSs) produced in parahydrogen. "The critical point in these experiments was driving Raman coherence adiabatically, that is, without dissipation," said Katsuragawa. "We achieved this by developing an injection-locked laser capable of emitting arbitrary pairs of two frequencies to irradiate the hydrogen gas, in order to control two photon detuning from the Raman resonance."

Recently, the UEC team has produced higher order series of stimulated Raman scattering using two driving lasers by the introduction of a second harmonic in one of the lasers. The resulting emission referred to as a 'Raman comb,' covered an octave spectrum range from the infrared to the ultraviolet.

"I am confident that our research has laid the foundations for the development of practical systems for the generation of trains of monocycle pulses with total control of the phase," noted Katsuragawa.

"Raman comb" generated by modulating single-frequency laser radiation with coherent molecular oscillations.