L. Salomon

An Evanescent Field Optical Microscope

We present a new form of optical microscope. An evanescent field is produced in the lower index medium of an ATR system and modulated by a sample deposited on the hypotenuse of the prism. A sharpened fiber optic probes this field and gives information about the topography of the surface.

Sample–tip coupling efficiencies of the photon-scanning tunneling microscope

The photon-scanning tunneling microscope is the photon analog to the electron-scanning tunneling microscope. It uses the evanescent field due to the total internal reflection of a light beam in a prism, modulated by a sample attached to the prism. The exponential decay of the evanescent field is characterized by the penetration depth dp and depends on the angle of incidence θ, the wavelength, and the polarization of the incident beam. The 1/e decay lengths range from 150 to 265 nm as deduced from the expression of the electric-field intensity in the rarer medium for θ = π/2. If we place another optically transparent medium near the surface, frustrated total reflection occurs. It is shown theoretically and experimentally that, if we choose an appropriate angle of incidence θ(θ ≠ π/2) and change the index of refraction of one of the media, the decay length of the electric field can be extremely small, so that images with an improved resolution can be produced.

Analysis of the Bloch mode spectra of surface polaritonic crystals in the weak and strong coupling regimes: grating-enhanced transmission at oblique incidence and suppression of SPP radiative losses

The Bloch mode spectrum of surface plasmon polaritons (SPPs) on a finite thickness metal film has been analyzed in the regimes of weak and strong coupling between SPP modes on the opposite film interfaces. The SPP mode dispersion and associated field distributions have been studied. The results have been applied to the description of the light transmission through thick and thin periodically structured metal films at oblique incidence. In contrast to normal incidence, all SPP Bloch modes on a grating structure participate in the resonant photon tunnelling leading to the transmission enhancement. However, at the angle of incidence corresponding to the crossing of different symmetry film SPP Bloch modes, the far-field transmission is suppressed despite the enhanced near-field transmission. The combined SPP mode consisting of the two film SPPs having different symmetries that is achieved at the crossing frequency exhibits no radiative losses on a structured surface.

Resolution of the photon scanning tunneling microscope: influence of physical parameters

Abstract The photon scanning tunneling microscope (PSTM) is the photon analogue of the electron scanning tunneling microscope (ESTM). It uses the evanescent field due to total internal reflection (TIR) of a light beam in a prism modulated by a sample placed on the base of the prism. Our experimental results shown details which present a lateral size as small as 200 A. The PSTM axial resolution is more difficult to evaluate. It is a function of the roughness of the sample. For very smooth samples, images shown an axial resolution of about 10 A. At last we discuss how both lateral and axial resolution can be affected by several parameters such as the tip surface distance and the roughness of the sample itself. This paper shows the necessity to find for each sample a good working distance where the profile follows as close as possible the shape of the sample.

How light gets through periodically nanostructured metal films: a role of surface polaritonic crystals.

The physical origin of the enhanced optical transmission of periodically structured films related to surface plasmon polaritons is discussed from first principles. The enhancement of transmission through smooth, randomly rough and periodically nanostructured films is considered. Analysis shows that any metal (or dielectric) nanostructured film can exhibit enhanced transmission in certain spectral ranges corresponding to surface plasmon (or phonon) polariton Bloch mode states on a periodic structure. Resonant tunnelling via these states is responsible for the transmission enhancement. The properties of surface polaritonic crystals are analogous to those of photonic crystals and can find numerous applications for scaling down optical devices to nanometric dimensions as well as for designing novel nanostructured materials whose optical properties are determined by surface polariton interaction in a periodic structure.

Observation of optical waveguides by using a photon scanning tunneling microscope

The photon scanning tunneling microscope (PSTM) is based on the frustration of total internal reflection by the apex of an optical fiber placed near the surface of reflection. It has so far been used to obtain topographic information. This article shows that it also allows one to reach local variations of the refractive index of the sample. The PSTM, like many local probes, is operated on a constant intensity level. In that case a theoretical analysis based on a simple model shows that a change of the refractive index can actually be seen with the PSTM. The authors find that the corrugation height depends on the distance between the tip and the sample surface. The local refractive index of microguides diffused in glass has been studied experimentally with the PSTM. Relative variations in the order of 10-3 have been observed.

Imaging of test quartz gratings with a photon scanning tunneling microscope. Experiment and theory

We use the differential formalism of the electromagnetic theory of gratings to interpret the images of test sinusoidal or lamellar quartz gratings obtained with a photon scanning tunneling microscope. The period of the grating is 0.5 μm, and the height of the rule is 0.2 μm. It is shown that the images depend strongly on several parameters, such as polarization or angle of incidence, with respect to the ruling direction. A systematic study of the isointensity lines above the gratings as a function of polarization is presented, and it is shown that the image contrast can be increased or decreased depending on the sample–probe distance. To model the interaction of the fiber probe with the electromagnetic field, we consider a second grating facing the grating under study, and by varying the periodicity of the second grating we calculate the intensity of the collected light and compare it with the experimental results.

Photon scanning tunneling microscope using incoherent polychromatic light

Abstract A photon scanning tunneling microscope (PSTM) using an incoherent polychromatic light source has been constructed and used to image submicronic structure in a constant intensity mode. The experimental values of the penetration depth of the incident electromagnetic field of the system are in good agreement with the theoretical values obtained with a three-media model. This new method for operating a PSTM offers a wide range of applications: determination of local indexes of refraction or local spectroscopies.

A dark field photon scanning tunneling microscope under incoherent light illumination

Abstract A new kind of photon scanning tunneling microscope which reduces the asymmetrical effects due to the illumination is described. The evanescent electromagnetic field is produces through a conventional dark field optical microscope condensor with a white incoherent light source. Images of quartz crossed grating are presented and compared to the spatial distribution of the calculated iso-intensity lines.

First images obtained in the near infrared spectrum with the photon scanning tunneling microscope

Abstract First images obtained in the near infrared spectrum with a photon scanning tunneling microscope are presented. The intensity of the light collected by the fibertip, at λ = 1.3 λm , which is a function of the separation between the tip and the sample surface is in agreement with that predicted by the theory. Images of quartz and silicon oxide are presented and the latter is compared with that obtained by an atomic force microscope.