B. N. Mironov

Femtosecond laser source of nanolocalized directed photoelectrons

A nanolocalized electron beam has been formed by electrons passing through a quartz microcapillary. The authors have demonstrated that such electrons are capable of producing the image of a dielectric nanoaperture. Using the capillary and a metal tip illuminated by femtosecond laser pulses, the authors have developed a photoelectron source based on nanolocalized photoelectron bunches with low angular divergence. It allows the observation of femtosecond-laser-induced processes on a surface with high temporal and spatial resolutions.

Towards the Fluorescence Resonance Energy Transfer (FRET) Scanning Near-Field Optical Microscopy: Investigation of Nanolocal FRET Processes and FRET Probe Microscope ¶

The fluorescence resonance energy-transfer (FRET) process is investigated between donor dye molecules deposited on the sample surface and acceptor dye molecules deposited on the tips of scanning near-field and atomic force microscopes. The FRET process was observed only when the tip acquired contact with the sample and took place in regions of sizes of only a few tens of nanometers with only a few thousands (or even hundreds) of molecules involved. The dependence of the FRET intensity on the tip-sample acting force is recorded and interpreted. In relation to the obtained results, the construction of a previously proposed one-atom FRET SNOM is described.

Formation of nanolocalized tungsten photoion packets by femtosecond laser pulses

Nanolocalized ion packets have been produced due to the transmission of photoions, which are emitted from a refractory metal emitter irradiated by femtosecond laser radiation with a high repetition rate, through a quartz nanocapillary. With the use of such a pulsed nanobeam, a miniature ion microscope has been created and the image of a dielectric-nanoaperture fragment has been obtained.

Analysis of fiber probes of scanning near-field optical microscope by field emission microscopy

It is shown that field emission microscopy and related methods can be used to analyze the metal coated fiber tips, which nowadays are the most frequently used sensor for the scanning near-field optical microscopy (SNOM). Metal free and thus non field-emitting aperture for the light transmission on the tip apex can be directly seen and its parameters can be measured, which is very important for the interpretation of SNOM data.

Laser Photoelectron Projection Microscopy of an Organic Conducting Polymer

A conducting organic polymer is visualized on a laser photoelectron projection microscope, which is based on Letokhov’s concept and has a nanometer spatial resolution. Photoelectron images of polyaniline (which is the most promising representative of conducting polymers) with a magnification of ∼105 have been obtained when a 100-nm quartz capillary coated with a film of this material was irradiated by femtosecond laser pulses. The projection photoelectron method using 400- and 800-nm laser radiation has made it possible to directly reveal the existence of the redox heterogeneity of the organic polymer, which is due to the contact of the sections of polyaniline with different oxidation degrees and strongly affects the electric conductivity of the sample.

Formation of an Electron Beam with a Duration Shorter than 100 fs during Photoemission of Electrons by Femtosecond Laser Pulses

Irradiation of a thin metal target by 38-fs laser pulses at a wavelength of 800 nm is shown to generate a beam of photoelectrons that contains a component whose duration is shorter than 100 fs. The ensemble of photoelectrons is formed by photoemission of a gold film about 10 nm thick sputtered on the base of a prism made of fused silica. The laser beam irradiates a dielectric-metal interface and propagates inside the prism at an angle of 45° to a normal to the interface. The photoelectron beam is formed by accelerating photoelectrons in a spatially inhomogeneous electrostatic potential. The ultrashort component of the photoelectron beam is found to be formed under the action of a ponderomotive potential. It is shown that the ultrashort electron component can be separated from the remaining part of the photoelectron beam with the help of an inhomogeneous electrostatic field.

Nonperturbing observation of optical near field

The spatial distribution of light intensity in the near field is studied by observing the photoelectron projection images of a subwavelength nanoaperture. The imaging electrons are obtained as a result of a two-photon external photoelectric effect induced in the aperture formed at the end of an optical fiber by femtosecond pulses of the second-harmonic radiation (410 nm) of a Ti:sapphire laser. The light-field distribution in the aperture is not distorted by any near-by object (such as a medium containing fluorescent molecules), which allows nonperturbing measurement of such a distribution.

Measurement of the Gaponov-Miller force produced in vacuum by tightly focused intense femtosecond laser radiation

A method for measuring the Gaponov-Miller force (GMF) is demonstrated based on the deflection of a picosecond photoelectron beam exposed to tightly focused intense femtosecond laser radiation. It is shown experimentally that the action of this force produced by femtosecond laser pulses linearly depends on their intensity. The method can be used to verify the correctness of measuring the duration of an ultrashort electron bunch based on the GMF.

Direct observation of the generation of coherent optical phonons in thin antimony films by the femtosecond electron diffraction method

The generation of coherent optical phonons in an antimony film has been directly observed by the femtosecond electron diffraction method. The sample has been excited by a femtosecond laser pulse (λ = 800 nm) and probed with a pulsed photoelectron beam. Oscillations of the intensity corresponding to vibration frequencies of optical phonons excited by the laser have been observed in the obtained diffraction patterns: totally symmetric (A1g) and twofold degenerate (E2g) phonon modes of antimony and their combinations.

Visualization of the spatio-temporal structure of a pulsed photoelectron beam formed by femtosecond laser radiation

A method based on an original electron microscope created for investigating photoelectron beams is presented. It ensures a nanometer spatial resolution and picosecond time resolution. Electrons appearing when a metal needle is irradiated by femtosecond laser pulses are transmitted through a dielectric microcapillary and are subjected to a ponderomotive potential created by femtosecond laser radiation focused near the capillary tip. The position-sensitive detection scheme allows for the detection of the spatial profile of a photo-electron beam with a magnification of K ≅ 4 × 104. The time structure of the photoelectron beam is visualized by scanning the delay time between laser pulses irradiating the needle and a laser pulse focused near the capillary tip.