Terahertz imaging with nanometer resolution

Chen, Hou-Tong; Kersting, R.; Cho, Gyu Cheon

doi:10.1063/1.1616668

Cited by 480 publications

(204 citation statements)

References 16 publications

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“…Very recently, there have been reports showing how ANSOM can be adapted for the terahertz (THz) frequency domain, by combining it with THz time-domain spectroscopy. [4][5][6][7] This is an exciting development, as it is becoming increasingly clear that many systems of interest, including biological molecules and a variety of artificial nanostructures, have absorption features in the THz frequency range, but are far smaller than the wavelength of the THz radiation. [8][9][10][11] These developments therefore offer great promise for THz microscopy.…”

mentioning

confidence: 99%

Antenna effects in terahertz apertureless near-field optical microscopy

Wang

Mittleman

Valk

et al. 2004

Applied Physics Letters

124

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We have performed measurements on terahertz (THz) apertureless near-field microscopy that show that the temporal shape of the observed near-field signals is approximately proportional to the time-integral of the incident field. Associated with this signal change is a bandwidth reduction by approximately a factor of 3 which is observed using both a near-field detection technique and a far-field detection technique. Using a dipole antenna model, it is shown how the observed effects can be explained by the signal filtering properties of the metal tips used in the experiments. Apertureless near-field scanning optical microscopy (ANSOM) is an attractive technique for obtaining subwavelength resolution in optical imaging at visible and midinfared wavelengths. [1][2][3] In this technique, light is scattered off a subwavelength-sized metal tip which is held close to a surface. The scattered light is collected in the far-field, giving subwavelength resolution in the immediate neighborhood of the tip apex. Very recently, there have been reports showing how ANSOM can be adapted for the terahertz (THz) frequency domain, by combining it with THz time-domain spectroscopy. [4][5][6][7] This is an exciting development, as it is becoming increasingly clear that many systems of interest, including biological molecules and a variety of artificial nanostructures, have absorption features in the THz frequency range, but are far smaller than the wavelength of the THz radiation. [8][9][10][11] These developments therefore offer great promise for THz microscopy. In the THz ANSOM experiments, two different detection techniques are currently employed: THz electric fields are either detected in the nearfield of the tip using electro-optic sampling, or in the far-field of the tip with a receiver. In the latter case, near-field information from the tip apex is obtained by vibrating the metal tip at a high frequency, followed by phase-sensitive detection at this frequency. However, an important aspect of both experiments remains unexplained: The measured temporal profile of the near-field signals is very different from that of the incident THz pulses. Associated with this shape change is a bandwidth reduction of about a factor of 3, which could limit the utility of the technique in spectroscopic measurements. For practical applications, such as THz microscopy, it is essential that the origin of this bandwidth reduction is understood.Here, we present measurements and calculations which demonstrate that the observed bandwidth reduction is a consequence of the antenna properties of the metal tips used in the experiments. We demonstrate that, regardless of whether the near-field signal is observed directly under the tip or in the far-field, it is approximately proportional to the timeintegral of the incident THz signal. Near-field calculations based on a dipole antenna model qualitatively reproduce all the essential features observed in the measurements and provide insight into ANSOM experiments in general.The two THz ANSOM configurations, used ...

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mentioning

confidence: 99%

Antenna effects in terahertz apertureless near-field optical microscopy

Wang

Mittleman

Valk

et al. 2004

Applied Physics Letters

124

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“…Accordingly, development of s-SNOM in the few THz region was initiated by employing the "time-domain" THz spectrometer where a train of sub-ps near-infrared pulses is used for both the generation of broadband 0.1-7 THz pulses, as also for their time-resolved sampling via a mechanical delay stage. One study of metal stripes was interpreted to demonstrate 150 nm spatial resolution, nonwithstanding the fact that the image was taken at a 1200 nm high topographical edge and also appeared in a faint contrast of only 0.5% [42]. When a sample modulation was employed higher contrast was reported but at deteriorated resolution of 1800 nm [43].…”

Section: Apertureless Near-field Microscopy Development From Microwavmentioning

confidence: 99%

Nanoscale Conductivity Contrast by Scattering-Type Near-Field Optical Microscopy in the Visible, Infrared and THz Domains

Keilmann

Huber

Hillenbrand

2009

J Infrared Milli Terahz Waves

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We demonstrate the wide application potential of optical near-field microscopy for mapping samples with locally varying conductivity. The apertureless, scattering-type optical near-field microscope (s-SNOM) operates on an AFM basis with an added lightscattering channel, wherein a standard cantilevered tip suffices to accomodate the full spectral range from visible to THz frequencies. The optical maps appear in amplitude and phase contrast, simultaneously with the topography map, at a spatial resolution of typically 20 nm. Visible and near-infrared operation is best suited for distinguishing metals, while a sensitive response to semiconductors is ideally provided with infrared and THz operation. Various types of conductivity spectral features can be explored in specific regions, corresponding to the elementary excitation linked to e.g. superconductivity, electron correlation, or low-dimensional conduction.

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“…Theoretical prediction is also important to estimate the behavior of the near-field light and the scanning probe [83]. The spatial resolution of apertureless THz imaging was reported to be 150 nm for 2 THz pulses by Kersting et al [84].…”

Section: Near-field Experiments In Thz Regionmentioning

confidence: 99%

Imaging and spectroscopy through plasmonic nano-probe

Saito

Verma

2009

Eur. Phys. J. Appl. Phys.

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Abstract. This article is a comprehensive review of the subject of near-field nano imaging and spectroscopy by surface plasmon polaritons induced on a metallized probe. The emphasis of the review is on fundamental aspects of plasmon enhancement and near-field spectroscopy, which are categorized as optical antenna structures, polarization properties in near-field, resonance frequency of surface plasmons, etc. Most recent studies that contribute to the understanding and interpretation of these phenomena are highlighted. Applications of near-field optics as newly established analytical tools for biology, materials sciences and plasmonic superlenses are included in the article.

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Terahertz imaging with nanometer resolution

Cited by 480 publications

References 16 publications

Antenna effects in terahertz apertureless near-field optical microscopy

Antenna effects in terahertz apertureless near-field optical microscopy

Nanoscale Conductivity Contrast by Scattering-Type Near-Field Optical Microscopy in the Visible, Infrared and THz Domains

Imaging and spectroscopy through plasmonic nano-probe

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