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2. Terahertz emission from transient currents and coherent phonons in layered MoSe$_2$ and WSe$_2$

Author

Afalla, Jessica, Muldera, Joselito, Takamizawa, Semmi, Fukuda, Takumi, Ueno, Keiji, Tani, Masahiko, and Hase, Muneaki

Subjects
Condensed Matter - Materials Science
Abstract

Terahertz (THz) time-domain emission spectroscopy was performed on layered 2H-MoSe2 and 2H-WSe2. The THz emission shows an initial cycle attributed to surge currents and is followed by oscillations attributed to coherent interlayer phonon modes. To obtain the frequencies of the interlayer vibrations, analysis of the THz emission waveforms were performed, separating the two contributions to the total waveform. Results of the fitting show several vibrational modes in the range of 5.87 to 32.75 cm-1 for the samples, attributed to infrared-active interlayer shear and breathing modes. This study demonstrates that THz emission spectroscopy provides a means of observing these low frequency vibrational modes in layered materials.

Published
2023
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5. Effect of heteroepitaxial growth on LT-GaAs: ultrafast optical properties

Author

Afalla, Jessica, Prieto, Elizabeth Ann, Husay, Horace Andrew, Gonzales, Karl Cedric, Catindig, Gerald, Abulikemu, Aizitiaili, Somintac, Armando, Salvador, Arnel, Estacio, Elmer, Tani, Masahiko, and Hase, Muneaki

Subjects
Condensed Matter - Materials Science
Abstract

Epitaxial low temperature grown GaAs (LT-GaAs) on silicon (LT-GaAs/Si) has the potential for terahertz (THz) photoconductive antenna applications. However, crystalline, optical and electrical properties of heteroepitaxial grown LT-GaAs/Si can be very different from those grown on semi-insulating GaAs substrates (reference). In this study, we investigate optical properties of an epitaxial grown LT-GaAs/Si sample, compared to a reference grown under the same substrate temperature, and with the same layer thickness. Anti-phase domains and some crystal misorientation are present in the LT-GaAs/Si. From coherent phonon spectroscopy, the intrinsic carrier densities are estimated to be ~$10^{15}$ cm$^{-3}$ for either sample. Strong plasmon damping is also observed. Carrier dynamics, measured by time-resolved THz spectroscopy at high excitation fluence, reveals markedly different responses between samples. Below saturation, both samples exhibit the desired fast response. Under optical fluences $\geq$ 54 $\mu$ J/cm$^2$, the reference LT-GaAs layer shows saturation of electron trapping states leading to non-exponential behavior, but the LT-GaAs/Si maintains a double exponential decay. The difference is attributed to the formation of As-As and Ga-Ga bonds during the heteroepitaxial growth of LT-GaAs/Si, effectively leading to a much lower density of As-related electron traps., Comment: 8 pages, supplementary info separate

Published
2021
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6. Terahertz emission improvement of gallium-arsenide-based bowtie photoconductive antenna by AAO-patterned gold nanoparticles integration on the photoconducting gap

Author

Dela Rosa, Lourdes Nicole, Alaba, Kenneth Jay, Cabello, Neil Irvin, Loberternos, Regine, Ferrolino, John Paul, Verona, Ivan Cedrick, Juguilon, Vince Paul, Salvador, Arnel, Somintac, Armando, Kitahara, Hideaki, De Los Reyes, Alexander, Bardolaza, Hannah, Tani, Masahiko, and Estacio, Elmer

Published
2024
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11. Efficient Terahertz Generation Using Fe/Pt Spintronic Emitters Pumped at Different Wavelengths

Author

Papaioannou, Evangelos Th., Torosyan, Garik, Keller, Sascha, Scheuer, Laura, Battiato, Marco, Mag-usara, Valynn Katrine, L'huillier, Johannes, Tani, Masahiko, and Beigang, René

Subjects
Physics - Applied Physics, Condensed Matter - Mesoscale and Nanoscale Physics
Abstract

Recent studies in spintronics have highlighted ultrathin magnetic metallic multilayers as a novel and very promising class of broadband terahertz radiation sources. Such spintronic multilayers consist of ferromagnetic (FM) and non-magnetic (NM) thin films. When triggered by ultrafast laser pulses, they generate pulsed THz radiation due to the inverse spin-Hall effect, a mechanism that converts optically driven spin currents from the magnetized FM layer into transient transverse charge currents in the NM layer, resulting in THz emission. As THz emitters, FM/NM multilayers have been intensively investigated so far only at 800-nm excitation wavelength using femtosecond Ti:sapphire lasers. In this work, we demonstrate that an optimized spintronic bilayer structure of 2-nm Fe and 3-nm Pt grown on 500 {\mu}m MgO substrate is just as effective as a THz radiation source when excited either at {\lambda} = 800 nm or at {\lambda} = 1550 nm by ultrafast laser pulses from a fs fiber laser (pulse width close to 100 fs, repetition rate around 100 MHz). Even with low incident power levels, the Fe/Pt spintronic emitter exhibits efficient generation of THz radiation at both excitation wavelengths. The efficient THz emitter operation at 1550 nm facilitates the integration of such spintronic emitters in THz systems driven by relatively low cost and compact fs fiber lasers without the need for frequency conversion.

Published
2018
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14. Terahertz emission from transient currents and coherent phonons in layered MoSe2 and WSe2.

Author

Afalla, Jessica, Muldera, Joselito, Takamizawa, Semmi, Fukuda, Takumi, Ueno, Keiji, Tani, Masahiko, and Hase, Muneaki

Subjects
PHONONS, EMISSION spectroscopy, FREQUENCIES of oscillating systems, OSCILLATIONS
Abstract

Terahertz (THz) time-domain emission spectroscopy was performed on layered 2H-MoSe 2 and 2H-WSe 2. The THz emission shows an initial cycle attributed to surge currents and is followed by oscillations attributed to coherent interlayer phonon modes. To obtain the frequencies of the interlayer vibrations, an analysis of the THz emission waveforms was performed, separating the two contributions to the total waveform. Results of the fitting show several vibrational modes in the range of 5.87–32.75 cm − 1 for the samples, attributed to infrared-active interlayer shear and breathing modes. This study demonstrates that THz emission spectroscopy provides a means of observing these low-frequency vibrational modes in layered materials. [ABSTRACT FROM AUTHOR]

Published
2023
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17. Optimization of terahertz emission from spintronic Fe/Pt hetero-structures

Author

Tani, Masahiko, primary, Talara, Miezel, additional, Bulgarevich, Dmitry, additional, Mag-usara, Valynn K., additional, Escaño, Mary C., additional, Kitahara, Hideaki, additional, Furuya, Takashi, additional, Nakajima, Makoto, additional, Watanabe, Makoto, additional, Torosyan, Garik, additional, and Beigang, René, additional

Published
2023
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24. Enhanced terahertz emission of a gallium arsenide thin film on a porous silicon distributed Bragg reflector designed at 800nm wavelength

Author

Jose, Ameera, Montecillo, Anthony, De Los Reyes, Alexander, Bacaoco, Miguel, Lopez, Joybelle, Cafe, Arven, Faustino, Maria Angela, Husay, Horace Andrew, Vasquez, John Daniel, Gonzales, Karl Cedric, Catindig, Gerald Angelo, Afalla, Jessica Pauline, Mag-usara, Valynn Katrine, Kitahara, Hideaki, Tani, Masahiko, Somintac, Armando, Salvador, Arnel, and Estacio, Elmer

Published
2019
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25. Temperature Dependence of the Conductivity of InSb Measured by Terahertz Time-Domain Spectroscopy

Author

Liu, Shuang, primary, Agulto, Verdad C., additional, Iwamoto, Toshiyuki, additional, Kato, Kosaku, additional, Mag-Usara, Valynn Katrine, additional, Ota, Masato, additional, Dolas, Shamika, additional, Newman, Nathan, additional, Nedelcu, Liviu, additional, Tani, Masahiko, additional, Yoshimura, Masashi, additional, and Nakajima, Makoto, additional

Published
2023
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27. Highly Efficient THz Waves Using Laser Chaos

Author

Kuwashima, Fumiyoshi, primary, Jarrahi, Mona, additional, Cakmakyapan, Semih, additional, Morikawa, Osamu, additional, Shirao, Takuya, additional, Iwao, Kazuyuki, additional, Kurihara, Kazuyoshi, additional, Kitahara, Hideaki, additional, Furuya, Takeshi, additional, Wada, Kenji, additional, Kawakami, Yuki, additional, Moriyasu, Takeshi, additional, Nakajima, Makoto, additional, and Tani, Masahiko, additional

Published
2023
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29. Attempt to Generate Narrow Linewidth, CW Terahertz Radiation by Using Optical Frequency Comb

Author

Iftiquar, S. M., Sakai, Kiyomi, Tani, Masahiko, Widiyatmoko, Bambang, Kourogi, Motonobu, and Otsu, Motoichi

Subjects
Physics - Optics
Abstract

We report on an attempt to generate highly stable continuous terahertz (THz) wave by using optical frequency comb (OFC). About 10-nm wide OFC has been generated through a deep phase modulation of a 852 nm laser line in lithium niobate crystal cavity. The multiple optical modes (side bands) of the OFC, which are equally separated from each other by the modulation frequency (=6 GHz) are taken as the frequency reference. When another semiconductor laser is frequency locked, the stability of the difference frequency between the master laser and the second laser is improved on the same order of the RF modulator. An ultra-narrow line and tunable THz radiation source can be achieved by photomixing of this stable difference-frequency optical beat in a photoconductive antenna., Comment: 3 pages, 3 figures

Published
2003

30. A modulation-doped heterostructure-based terahertz photoconductive antenna emitter with recessed metal contacts

Author

Afalla, Jessica, De Los Reyes, Alexander, Cabello, Neil Irvin, Vistro, Victor DC Andres, Faustino, Maria Angela, Ferrolino, John Paul, Prieto, Elizabeth Ann, Bardolaza, Hannah, Catindig, Gerald Angelo R., Gonzales, Karl Cedric, Mag-usara, Valynn Katrine, Kitahara, Hideaki, Somintac, Armando S., Salvador, Arnel A., Tani, Masahiko, and Estacio, Elmer S.

Published
2020
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37. Production of high power femtosecond terahertz radiation

Author

Neil, George R., Carr, G.L., Gubeli, Joseph F., Jordan, K., Martin, Michael C., McKinney, Wayne R., Shinn, Michelle, Tani, Masahiko, Williams, G.P., and Zhang, X.-C.

Subjects
Linac THz Coherent Recirculation
Abstract

The terahertz (THz) region of the electromagnetic spectrum is attracting interest for a broad range of applications ranging from diagnosing electron beams to biological imaging. Most sources of short pulse THz radiation utilize excitation of biased semiconductors or electro-optic crystals by high peak power lasers. For example, this was done by using an un-doped InAs wafer irradiated by a femtosecond free-electron laser (FEL) at the Thomas Jefferson National Accelerator Facility. Microwatt levels of THz radiation were detected when excited with FEL pulses at 1.06 mm wavelength and 10W average power. Recently substantially higher powers of femtosecond THz pulses produced by synchrotron emission were extracted from the electron beamline. Calculations and measurements confirm the production of coherent broadband THz radiation from relativistic electrons with an average power of nearly 20W, a world record in this wavelength range by a factor of 10,000. We describe the source, presenting theoretical calculations and their experimental verification. Potential applications of this exciting new source include driving new non-linear phenomena, performing pump-probe studies of dynamical properties of novel materials, and studying molecular vibrations and rotations, low frequency protein motions, phonons, superconductor band gaps, electronic scattering, collective electronic excitations (e.g., charge density waves), and spintronics.

Published
2002

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