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Ramakrishnan, G. (author), Chakkittakandy, R. (author), Planken, P.C.M. (author)
Generation of subpicosecond terahertz pulses is observed when graphite surfaces are illuminated with femtosecond near-infrared laser pulses. The nonlinear optical generation of THz pulses from graphite is unexpected since, in principle, the material possesses a centre of inversion symmetry. Experiments with highly oriented pyrolytic graphite...
journal article 2009
document
Ramakrishnan, G. (author), Planken, P.C.M. (author)
Emission of pulses of electromagnetic radiation in the terahertz range is observed when ultrathin gold films on glass are illuminated with femtosecond near-IR laser pulses. A distinct maximum is observed in the emitted terahertz amplitude from films of average thickness just above the percolation threshold. Our measurements suggest that the...
journal article 2011
document
Ramakrishnan, G. (author), Kumar, N. (author), Planken, P.C.M. (author), Tanaka, D. (author), Kajikawa, K. (author)
Emission of terahertz radiation is observed when surface plasmons are excited on a thin film of gold, in the Kretschmann geometry. When a hemicyanine-terminated alkanethiol self-assembled monolayer of thickness 1.2 nm is deposited on the gold film, stronger terahertz emission is observed. Our experimental results confirm that enhanced terahertz...
journal article 2012
document
Ramanandan, G.K.P. (author), Ramakrishnan, G. (author), Planken, P.C.M. (author)
Terahertz (THz) transmission spectroscopy is used to measure the oxidation kinetics of copper thin films evaporated on silicon substrates. The transmission of broadband THz pulses from 1 to 7 THz through the copper film is measured while it gets oxidized at an elevated temperature in ambient air. The change in the transmitted THz electric field...
journal article 2012
document
Kajikawa, K. (author), Nagai, Y. (author), Uchiho, Y. (author), Ramakrishnan, G. (author), Kumar, N. (author), Ramanandan, G.K.P. (author), Planken, P.C.M. (author)
Electromagnetic wave emission based on optical rectification at terahertz (THz) wavelengths was observed from surface-immobilized gold nanospheres (SIGNs) above a gold surface. Although the excitation wavelength is off-resonant with the localized surface plasmons, the THz emission field was observed to be approximately 4.8 times greater than...
journal article 2012
document
Ramakrishnan, G. (author), Planken, P.C.M. (author)
patent 2012
document
Ramakrishnan, G. (author), Ramanandan, G.K.P. (author), Adam, A.J.L. (author), Xu, M. (author), Kumar, N. (author), Hendrikx, R.W.A. (author), Planken, P.C.M. (author)
We report on the surprisingly strong, broadband emission of coherent terahertz pulses from ultrathin layers of semiconductors such as amorphous silicon, germanium and polycrystalline cuprous oxide deposited on gold, upon illumination with femtosecond laser pulses. The strength of the emission is surprising because the materials are considered to...
journal article 2013
document
Ramanandan, G.K.P. (author), Adam, A.J.L. (author), Ramakrishnan, G. (author), Petrik, P. (author), Hendrikx, R. (author), Planken, P.C.M. (author)
We show that the interface between gold and thermally formed cuprous oxide, which emits terahertz radiation when illuminated with ultrafast femtosecond lasers, is in fact an AuCu/Cu2O interface due to the formation of the thermal diffusion alloy AuCu. The alloy enables the formation of a Schottky-barrier-like electric field near the interface...
journal article 2014
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