39th Int. Conf. on Infrared, Millimeter, and THz Waves
September 14-19, 2014
The University of Arizona, Tucson, AZ
M3/E - 12. Material Science I
Monday, September 15, 2014 2:00 pm to 3:30 pm
Room: Santa Rita Room
Chairperson: Rene Beigang
2:00 pm 2:00 pm : Intense Terahertz Magnetic Fields Are Used To Control The Magnetization State Of Ferromagnetic Cobalt Thin Film. The Dynamics Visualized By Magneto Op
Presenter: Mostafa Shalaby

controlling magnetization dynamics by an ultrashort stimulus is attracting interest both in fundamental and applied sciences because of the potential to achieve magnetic switching at ever-faster speed. Femtosecond laser pulses have been used in the past to induce fast de-magnetization in ferromagnets [1]. In those experiments optical pulses manipulate incoherently the magnetization by ultrafast heating the electronic system above the Curie temperature. The subsequent cooling dynamics were orders of magnitude slower and limit re-access time to nanoseconds. A novel laser-matter magnetization control is possible thanks to the advent of non-ionizing, high-field Terahertz (THz) pulses. In the presented results, the unique THz pulses [2] induce non-resonant ultrafast magnetization dynamics. The magnetization response is phase-locked to the THz magnetic field carrier and thus follows exactly the ultra-strong, phase-stable oscillation. Moreover the laser's field phase and magnitude are directly imprinted onto the magnetization response, in absence of any resonant mode. This becomes possible since the off-resonant phase-locking mechanism presented here, injects only minor entropy into the system.

Author(s):
Mostafa Shalaby - PSI
Clemens Ruchert - PSI
Peter Derlet - PSI
Christoph Hauri - PSI/EPFL
B Tudu - UPMC
Jan Luning - UPMC
Carlo Vicario - PSI
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2:30 pm 2:30 pm : Progress On Mn-Co-Ni-O Infrared Thin Films And Detectors
Presenter: Zhiming Huang

High quality Mn-Co-Ni-O (MCN) spinel films are prepared on Al2O3 substrate by RF magnetron sputtering (RF) and chemical solution deposition (CSD). The microstructural characterizations reveal the films present excellent crystallization and compact surface. The variable temperature electrical results show the films have temperature coefficient of resistance (TCR) of --3.8 %/K at 295 K. Based on the electrical results of CSD-MCN films in 130~304 K, we find that the hopping exponent p of small polaron hopping conduction shows a clear variation from a value of 0.46 in the paramagnetic to 0.91 in the ferromagnetic phase at around 200 K. The mid-infrared optical properties of the films are obtained by fitting the measured ellipsometric parameter data using the classical infrared model. MCN film detectors are fabricated by photolithography follow by wet etching process to evaluate the applications for infrared detection. It exhibits a noise equivalent temperature difference as low as 2.1?10-7 K/Hz1/2, responsivity of 330 V/W, and detectivity of 0.6?108 cmHz1/2/W at 30 Hz. The 8?1 element MCN detector array is also successfully fabricated, and the response uniformity is about 5.9 %.

Author(s):
Zhiming Huang - Shanghai Institute of Technical Physics, CAS
Cheng OuYang - Shanghai Institute of Technical Physics, CAS
Wei Zhou - Shanghai Institute of Technical Physics, CAS
Jingchao Tong - Shanghai Institute of Technical Physics, CAS
Jingguo Huang - Shanghai Institute of Technical Physics, CAS
Junhao Chu - Shanghai Institute of Technical Physics, CAS
Jing Wu - Shanghai Institute of Technical Physics, CAS
Yanqing Gao - Shanghai Institute of Technical Physics, CAS
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2:45 pm 2:45 pm : Carrier Multiplication In Bulk Silicon Investigated By Terahertz Spectroscopy
Presenter: Genki Yamashita

We studied the carrier multiplication efficiency in bulk silicon using optical-pump/THz-probe spectroscopy. By the close analysis of the time resolved data, we observed the enhancement of the quantum efficiency due to carrier multiplication for incident photon energy above 4.1 eV. It agrees well with the results of photo current measurements. We believe that the present results enable us to correlate the results of quantum efficiency measurements of nano-structured materials and bulks.

Author(s):
Genki Yamashita - Osaka University
Eiichi Matsubara - Osaka Dental University
Masaya Nagai - Osaka University
Yoshihiko Kanemitsu - Kyoto University
Masaaki Ashida - Osaka University
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3:00 pm 3:00 pm : Time-resolved THz Dynamics In Thin Films Of Bi2Se3
Presenter: Dmitry Yarotski

Topological insulators represent a new state of matter where bulk insulators exhibit metallic surfaces that are protected by time reversal symmetry. However, in common transport measurements residual bulk conductivity hinders the properties of the topologically protected surfaces. Alternatively, terahertz spectroscopy has recently been shown to be capable of discerning the bulk and surface carrier conductivity. Here we use time-resolved optical pump-THz probe spectroscopy at low temperatures to study the hot carrier response of thin films of Bi2Se3 of several thicknesses and separate the bulk from the surface response. We find that for thinner films the photo excitation changes the transport scattering rate and reduces the surface conductivity. For thicker films, this process competes with the photoinduced increase in bulk conductivity, which occurs on shorter timescales and scales with the increase in both the film thickness and optical excitation fluence. These different dynamics of the surface and bulk electrons indicate a decoupling of surface and bulk carriers, and present the possibility of accessing long-lived surface photo-carriers for optoelectronic applications.

Author(s):
Dmitry Yarotski - Los Alamos National Laboratory
Rolando Valdes Aguilar - Ohio State University
Jingbo Qi - The PEAC Institute of Multiscale Sciences
Matthew Brahlek - Rutgers University
Namrata Bansal - Rutgers University
Abul Azad - Los Alamos National Laboratory
Seongshik Oh - Rutgers University
Antoinette Taylor - Los Alamos National Laboratory
Rohit Prasankumar - Los Alamos National Laboratory
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3:15 pm 3:15 pm : Pump Polarization Dependence Of Optical Rectification For 112A GaAs
Presenter: John Mabon

A general theory for the probe polarization angle dependence of optical rectification has been constructed. Measurements have been taken of 112A GaAs and compared to this theory. The terahertz radiation generated is a mixture of bulk (second order) and surface (third order) contributions. From this data, and a previous investigation into the azimuthal angle dependence of these samples, a value of the term in the third order non-linear polarization can be achieved.

Author(s):
Colin Bleasdale - University of Wollongong
John Mabon - University of Wollongong
Roger Lewis - University of Wollongong
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