Optical rectification in self-assembled monolayers probed at surface plasmon resonance condition

Uzawa, Ryohei; Tanaka, Daisuke; Okawa, Haruki; Hashimoto, Kazuhiko; Kajikawa, Kotaro

doi:10.1063/1.3179466

Cited by 8 publications

(13 citation statements)

References 16 publications

(23 reference statements)

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“…No measurable amount of THz radiation is observed when the film is excited directly from the airside, strongly suggesting that surface plasmon excitation increases the THz yield. When the Au surface is covered with a SAM of hemicyanine terminated alkanethiol molecules, the emitted THz electric field amplitude increases by a factor of about three, confirming the prediction made earlier by Uzawa et al [15,16]. The results emphasize the role played by surface plasmons in the generation of THz radiation and show that even a single (oriented) monolayer of molecules with a thickness of 1.2 nm can lead to significantly enhanced THz emission in this geometry, compared to a bare Au surface [17].…”

Section: Introductionsupporting

confidence: 78%

“…The dip in the reflected pump power observed around θ = 42°corresponds to the angle where surface plsmons are excited at the Au surface. We note that compared to the results reported in references [15,16], a broader resonance is seen in Fig. 4(a).…”

Section: Thz Emission From Self-assembled Monolayer Of Hemicyaninementioning

confidence: 57%

“…This enhancement is very similar to the surface-plasmon mediated enhancement of other nonlinear processes like SHG and Raman scattering reported from metal surfaces [21,23]. The ATR geometry is very suitable for the excitation of very thin (of a few nanometers) layers of nonlinear materials, because of the strong field localization near the metal surface [15]. In the ATR geometry, the pump beam is focused on the hypotenuse side of the prism to a spot size of diameter ∼ 1 mm.…”

Section: Thz Emission From Self-assembled Monolayer Of Hemicyaninementioning

confidence: 85%

“…In this context, it is very interesting that, recently, Uzawa et al reported OR of nanosecond laser pulses by a self-assembled monolayer (SAM) of hemicyanine-terminated alkanethiol molecules on an Au coated glass prism, using surface plasmon excitation in the attenuated total reflection (ATR) geometry [15]. The authors suggested that the same geometry could, in principle, be used to generate THz radiation from such a layer if femtosecond laser pulses are used.…”

Section: Introductionmentioning

confidence: 99%

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Surface plasmon-enhanced terahertz emission from a hemicyanine self-assembled monolayer

Ramakrishnan¹,

Kumar²,

Planken³

et al. 2012

Opt. Express

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Abstract: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 emission is possible from planar gold surfaces when surface plasmons are excited.

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Section: Introductionsupporting

confidence: 78%

Section: Thz Emission From Self-assembled Monolayer Of Hemicyaninementioning

confidence: 57%

Section: Thz Emission From Self-assembled Monolayer Of Hemicyaninementioning

confidence: 85%

Section: Introductionmentioning

confidence: 99%

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Surface plasmon-enhanced terahertz emission from a hemicyanine self-assembled monolayer

Ramakrishnan¹,

Kumar²,

Planken³

et al. 2012

Opt. Express

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“…Optical rectification (OR) is a second-order nonlinear optical (NLO) phenomenon that produces static dipoles by illumination with a high power laser pulse [1,2]. When ultrafast laser pulses are used, electromagnetic (EM) waves are radiated in the terahertz (THz) range because the laser pulses are rectified.…”

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confidence: 99%

Terahertz emission from surface-immobilized gold nanospheres

et al. 2012

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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 offresonant with the localized surface plasmons, the THz emission field was observed to be approximately 4.8 times greater than that from a percolated gold thin film of 10 nm thickness. A theoretical calculation predicts that the light electric field is enhanced in the SIGN system, even at off-resonance wavelengths. The observed THz field amplitude was quadratic with the illumination light field, suggesting that the THz generation is due to a second-order nonlinear optical process. showed THz generation at gold and silver surfaces [3]. A metallic surface shows second-order NLO activity because of the lack of an inversion center near the surface. Later they reported OR-based THz generation in thick metal films (100-200 nm thick), and attributed the optical nonlinearity to nonlocal effects [4]. On the other hand, Ramakrishnan and Planken have reported THz emission from a thin percolated gold film of 10 nm thickness, having localized surface plasmon (LSP) hot spots [5]. Recently Ramakrishnan et al. observed THz emission from ordered NLO chromophores in a molecular monolayer at the surface plasmon resonance condition [6]. In these studies, the THz emission amplitude is quadratic in the excitation field, suggesting that the THz emission is based on the second-order NLO process. On the contrary, Welsh et al. [7] and Polyushkin et al.[8] observed a non-quadratic dependence of the THz emission amplitude on the incident electric field. They attributed the THz emission from the metallic surface to multiphoton ionization and ponderomotive acceleration of electrons in the evanescent field produced by surface plasmons. This process may be called gindirect OR. These different observations suggest that different THz generation mechanisms are possible at gold surfaces.In this letter, we report THz emission from surfaceimmobilized gold nanospheres (SIGNs) above a gold surface with a gap distance of less than 1 nm. The SIGN structure is schematically illustrated in Fig. 1(a). The gap between the SIGN and the surface is supported by an aminoundecanethiol (AUT) self-assembled monolayer (SAM). The SIGNs show an intense resonance of LSPs, as a result of the EM interaction between the SIGNs and the gold surface [9][10][11][12][13]. Second-order NLO optical phenomena, second-harmonic generation (SHG) [10,11], OR and the Pockels effect [12], have been observed from the SIGNs, since the SIGN structure is noncentrosymmetric. Here, THz emission was observed from the SIGNs and its amplitude was found to be quadratic in the excitation field amplitude. This indicates that the THz generation is due to a second-order NLO process.The SIGN sample was prepared by the following procedure: As a substrate, a 100 nm thick thin gold film was vacuum-evaporated on a glass slide. The surface was covered with an AUT SAM, by dipping the gold subs...

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Formation Process of Self-Assembled Monolayer on Gold Nanosphere Probed by Second Harmonic Generation

et al. 2010

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The formation process of a hemicyanine-terminated alkanethiolate self-assembled monolayer (SAM) on gold nanospheres immobilized on a glass substrate was studied by absorption spectroscopy, optical second harmonic generation, and Monte Carlo simulation. It was found that hemicyanine thiolate SAMs mainly form in the upper hemisphere region of the gold nanospheres in the early stage, followed by the additional SAM formation in the lower region of gold nanospheres. The hemicyanine SAM does not homogeneously form over the nanosphere surface and does not fully cover the nanospheres even after long exposure to the hemicyanine solution. This is because of the narrow space under the nanosphere, where the binding of the alkane disulfide to the gold surface is considered to be a diffusion-controlled reaction. The orientation of the hemicyanine molecules on gold nanospheres is similar to that of hemicyanine on a flat gold substrate. These results are important to understand the surface chemistry at nanostructure surfaces as well as the localized surface plasmon biosensing using metallic nanostructures.

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Optical rectification in self-assembled monolayers probed at surface plasmon resonance condition

Cited by 8 publications

References 16 publications

Surface plasmon-enhanced terahertz emission from a hemicyanine self-assembled monolayer

Surface plasmon-enhanced terahertz emission from a hemicyanine self-assembled monolayer

Terahertz emission from surface-immobilized gold nanospheres

Formation Process of Self-Assembled Monolayer on Gold Nanosphere Probed by Second Harmonic Generation

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