Abstract-Porosity dependence of terahertz emission of porous silicon investigated using reflection geometry terahertz time-domain spectroscopy

• Arvin I. Mabilangan¹, 
• Lorenzo P. Lopez Jr.², 
• Maria Angela B. Faustino², 
• Joselito E. Muldera¹, 
• Neil Irvin F. Cabello^1, , , 
• Elmer S. Estacio^1, 2, 
• Arnel A. Salvador^1, 2, 
• Armando S. Somintac^1, 2

• ¹ Condensed Matter Physics Laboratory, National Institute of Physics, University of the Philippines, Diliman 1101, Quezon City, Philippines
• ² Materials Science and Engineering Program, University of the Philippines, Diliman 1101, Quezon City, Philippines
• http://www.sciencedirect.com/science/article/pii/S0749603616312629
• 
  

Porosity dependent terahertz emission of porous silicon (PSi) was studied. The PSi samples were fabricated via electrochemical etching of boron-doped (100) silicon in a solution containing 48% hydrofluoric acid, deionized water and absolute ethanol in a 1:3:4 volumetric ratio. The porosity was controlled by varying the supplied anodic current for each sample. The samples were then optically characterized via normal incidence reflectance spectroscopy to obtain values for their respective refractive indices and porosities. Absorbance of each sample was also computed using the data from its respective reflectance spectrum. Terahertz emission of each sample was acquired through terahertz - time domain spectroscopy. A decreasing trend in the THz signal power was observed as the porosity of each PSi was increased. This was caused by the decrease in the absorption strength as the silicon crystallite size in the PSi was minimized.

Abstract-Confined photocarrier transport in InAs pyramidal quantum dots via terahertz time-domain spectroscopy

Jorge Michael M. Presto, Elizabeth Ann P. Prieto, Karim M. Omambac, Jessica Pauline C. Afalla, Deborah Anne O. Lumantas, Arnel A. Salvador, Armando S. Somintac, Elmer S. Estacio, Kohji Yamamoto, and Masahiko Tani

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-23-11-14532

We present experimental demonstration of photocarrier dynamics in InAs quantum dots (QDs) via terahertz (THz) time-domain spectroscopy (TDS) using two excitation wavelengths and observing the magnetic field polarity characteristics of the THz signal. The InAs QDs was grown using standard Stranski-Krastanow technique on semi-insulating GaAs substrate. Excitation pump at 800 nm- and 910 nm-wavelength were used to distinguish THz emission from the InAs/GaAs matrix and InAs respectively. THz-TDS at 800 nm pump revealed intense THz emission comparable to a bulk p-InAs. For 910 nm pump, the THz emission generally weakened and upon applying external magnetic field of opposite polarities, the THz time-domain plot exhibited anomalous phase-shifting. This was attributed to the possible current-surge associated with the permanent dipole in the QD.

© 2015 Optical Society of America

Full Article  |  PDF Article

Abstract-Fast-Scan Terahertz Time Domain Spectrometer Based on Laser Repetition Frequency Modulation

Takashi Furuya1, Elmer S. Estacio1, Kazuki Horita1, Christopher T. Que1, Kohji Yamamoto1, Fumiaki Miyamaru2, Seizi Nishizawa2,3 and Masahiko Tani1

1 Research Center for Development of Far-Infra Red Region, University of Fukui, Fukui 910-8507, Japan
2 Shinshu University, Matsumoto, Nagano 390-8621, Japan
3 Advanced Infrared Spectroscopy Co., Ltd., Hachioji, Tokyo 193-0835, Japan 

http://iopscience.iop.org/1347-4065/52/2R/022401/

We propose a high-speed scanning terahertz (THz) time-domain spectrometer (TDS) based on optical sampling by repetition frequency modulation (OSREFM) using a repetition-frequency-tunable femtosecond fiber laser. Repetition frequency modulation is controlled by a highly stabilized external sweep generator. The fast scan of the time-delay between the pump and probe pulses is similar to an optical sampling with cavity tuning (OSCAT) THz-TDS system. However, the advantage of this technique is that it does not require physically moving components and uses only one laser system having an electronically modulated repetition rate. The time window and scanning time of this system depend on the modulation frequency range and the sweeping speed of the laser. In this study, we demonstrate the acquisition of a ~300 ps-window THz time waveform within 3 ms at a scan rate of 333 Hz.