B. Bölger

Near‐field optical microscope using a silicon‐nitride probe

Operation of an alternative near‐field optical microscope is presented. The microscope uses a microfabricated silicon‐nitride probe with integrated cantilever, as originally developed for force microscopy. The cantilever allows routine close contact near‐field imaging on arbitrary surfaces without tip destruction. The effect of adhesion forces on the coupling to the evanescent wave has been observed. Images with a lateral resolution of about 50 nm are presented and compared with atomic force images. A specific sample area can be selected using an integrated conventional light microscope.

Near-field optical microscopy in transmission and reflection modes in combination with force microscopy

Near‐field optical microscopy is the optical alternative of the various types of scanning probe microscopes. The technique overcomes the classical diffraction limit in conventional optical microscopy. In this paper the concepts of near‐field optics (NFO) are introduced, followed by a short review of current trends in NFO microscopy. Specifically, developments concerning the efficiency and versatility of both aperture and dielectric probe types are discussed. We present our advances in NFO microscopy, using both fibres and integrated silicon nitride (SiN) structures as dielectric probes. The use of an SiN probe as a combined optical and force sensor is shown to be advantageous, as it provides a feedback mechanism and allows direct comparison between topography and dielectric effects. Images of technical and biological samples are presented with a lateral resolution down to 20 nm, depending on the microscopical arrangement used.

Operation of a scanning near-field optical microscope in reflection in combination with a scanning force microscope

Images obtained with a scanning near field optical microscope (SNOM) operating in reflection are presented. We have obtained the first results with a SiN tip as optical probe. The instrument is simultaneously operated as a scanning force microscope (SFM). Moreover, the instrument incorporates an inverted light microscope (LM) for preselection of a scan area. The SiN probe is operated in the contact regime causing a highly improved lateral resolution in the optical image compared to an alternative set-up using a fiber probe, which is also presented. The combined microscope is operated either in open loop or as a force regulated SNOM. Near field optical images can be directly compared with the topography displayed in the simultaneously recorded SFM image.

Evanescent-field optical microscopy: effects of polarization, tip shape and radiative waves

Recent results in evanescent-field optical microscopy are presented. A resolution of 30 nm in the lateral directions and 0.1 nm in height has been obtained by suitable tip fabrication. Both the direction of the exciting field and the tip shape are shown to affect the optical coupling efficiency and resolution. Near-field diffraction patterns are observed with high lateral resolution by interference between evanescent and propagating waves.

Novel calixarenes in thin films for efficient second harmonic generation

Calix[4]arenes are a novel type of molecules for nonlinear optics. In a single molecule four pi-conjugated systems are combined. Corona poled guest-host polymer systems [calix[4]arenes-poly(methyl-methacrylate)] with transparency into the UV and loading up to 100% show a high degree of orientation. The maximum resonant d33 nonlinear coefficient measured at a fundamental wavelength of 590 nm is 51 pm/V. The d33 values of the thin films relax after poling to 65% of their maximum value. Results indicate self-organization of the molecules upon poling.

Optical contrast in near-field techniques

In this paper results of experiments with a scanning near-field optical microscope with shear-force feedback are presented. The setup will be described and the shear-force signal as function of distance is shown. Images of latex spheres and Langmuir- Blodgett layers of pentacosa-acid with about 100 nm lateral resolution are presented which show a true optical contrast due to fluorescence and polarization.

Čerenkov-type second-harmonic generation in thin planar calix[4]arene waveguiding films

A new type of organic molecule, calix[4]arene, is applied in a second-harmonic-generating waveguide device for the first time. Linear optical properties of the calix[4]arene waveguiding film have been measured with the prism-coupling method. The molecules in the film are oriented by a corona-poling technique. With a Maker-fringe experiment, the induced d(33) and d(31) at lambda = 1064 nm are determined at 8.6 and 2.0 pm/V, respectively. The calix[4]arene thin film has been applied to a Cerenkov-type device that generates second- harmonic light radiating into the glass substrate. The highest efficiency obtained is 0.23% for a fundamental wavelength of 820 nm by the use of fundamental power densities of 100 MW/cm(2) in the waveguide and a device length of 6 mm. A coupled-mode theory has been developed that can properly explain the experimentally observed second-harmonic-generating efficiency and the angle of radiation into the substrate. Two methods for the enhancement of device efficiency are proposed, both based o?n theoretical calculations with the coupled-mode theory. An enhancement of 2 orders of magnitude is feasible

Combined Photon Scanning Tunneling Microscope and Atomic Force Microscope using Silicon Nitride Probes

A Photon Scanning Tunneling Microscope is presented in which Si3N4 cantilevers are used as optical probes. This method allows close contact scanning without tip destruction. Simultaneous measurement of the optical signal and the deflection of the cantilever permits a comparison between the optical image and the topography. The optical signal as a function of the distance clearly shows the exponential behaviour of the evanescent field. Several structures have been examined, giving a lateral resolution in the optical image of about 40 nm.

An Evanescent Field Optical Microscope

An Evanescent Field Optical Microscope (EFOM) is presented, which employs frustrated total internal reflection on a highly localized scale by means of a sharp dielectric tip. The coupling of the evanescent field to the sub‐micrometer probe as a function of probe‐sample distance, angle of incidence and polarization has been characterized quantitatively both experimentally and theoretically. The coupling efficiency of light into the tip agrees with a description based on complex Fresnel coefficients. By scanning the tip images have been obtained of non‐conducting dielectric samples, periodic gratings and non periodic structures, containing both topographic and dielectric information which clearly demonstrate the capacity of the evanescent field optical microscope for nanometer scale optical imaging. The effect of field gradient, tip‐sample distance, polarization direction and tip artifacts on the images has been investigated. Recent results are presented.

Second harmonic generation of diode laser radiation in KNbO3

Both CW and pulsed diode lasers covering the wavelength region 855-912 nm have been investigated for the frequency doubling in KNbO. The influence of the spectral distribution mode character and the optical geometry of the laser beam have been investigated for several AlGaAs diode lasers. Second harmonic radiation with maximum efficiency of typically 1 has been detected both by temperature tuning CT 10-130 C noncritical phase matching) and by angle tuning. Results clearly demonstrate the critical aspects of the laser mode spectrum and the beam geometry as to the phase matching criterion in frequency doubling.