Immanuel Kant Baltic Federal University

Materials For Nanophotonics – Optical Investigations Optical Deposition Methods

Magnetophotonics is an active area of investigation and an increasing number of research groups are exploring this phenomenology from the experimental and theoretical viewpoints. The renewed interest in this field is strongly linked to the enhancement of the magnetooptical activity trough nanostructuration and the development and fast growth of magnetoplasmonics, studying the effects arising from the interplay between plasmonic and magneto-optical (MO) phenomena typically occurring in metallic nanostructures. Magnetoplasmonic nanosystems can improve the functionalities of traditional optical devices with novel active features triggered by the magnetic field. Specific applications are in gas and biosensing areas and in integrated photonic devices for telecommunications.

5a) Phemtosecond Magnetophotonics

(Tatyana V. Dolgova)

Femtosecond laser will be applied in studies of optical, magneto-optical and nonlinear-optical effects in nanostructures. Active control of optical signals in the time domain is what science and technology demand in fast all-optical information processing. Nanostructured materials can modify the group velocity and slow the light down, as the artificial light dispersion emerges. The time-resolved polarization rotation will be investigated within a single femtosecond laser pulse under conditions of slow light in magnetophotonic crystals – photonic crystals with functional magnetic layers. Slow light is a unique phenomenon related to the low group velocity. This phenomenon provides science and technology with a new outlook on fast all-optical information processing and striking physical effects. The Faraday rotation of the wave envelope of the laser pulse depends on the difference between the inverse group and phase velocities. Thus, slow light and Faraday rotation are the direct counterparts that represent the effective time of light-matter interaction. For compact magneto-optical devices in data processing, magnetophotonic crystals might be more suitable as the normalized effects are higher than in thin films. The results might be useful for the femtosecond polarization pulse shaping with the advantage of magnetic-field control in the next-generation photonic devices.The research plan will developed as follows:

- Development of the experimental setup for time-resolved magneto-optical spectroscopy based on tunable femtosecond laser system with temporal resolution up to 10 fs, which combines a polarization-sensitive technique with an autocorrelator of femtosecond pulses.

- Modeling the time-resolved Faraday rotation in magnetophotonic crystals based on the combination of the 4 x 4 transfer-matrix formalism and fast Fourier transformation. The software for calculating the time-resolved polarization rotation inside a single femtosecond laser pulse will be developed using the Python programming language.

- Experimental observation of ultrafast Faraday rotation dynamics in magnetophotonic crystals caused by femtosecond laser-pulse self-interference in the structured media.The observation of these effects is scientifically very interesting since ity might be applied to the fast control of light in high-capacity photonic devices.

5b) Influence of Bloch surface waives magneto-optical Faraday and Kerr effects in magnetophotonic crystals

(Irina Soboleva)

        The influence of Bloch surface waives magneto-optical Faraday and Kerr effects in magnetophotonic crystals will be investigated. Bloch surface electromagnetic waves (SEW) in photonic crystals are surface states in all-dielectric multilayer structures and are often considered as analogues of the dielectric surface plasmons in metal films. The SEW propagate along the surface and decay exponentially with distance from the surface of the photonic crystal, providing a significant increase in the local field near the surface. The polarization selectivity of the SEW is previously demonstrated. Depending on the photonic crystal structure, the SEW are observed only for one of the linear polarizations of the incident light. Due to the low absorption coefficients of dielectric materials constituting the photonic crystal, the SEW resonance demonstrates a large mean free path, that leads to a narrow spectral width and a high Q-factor of the SEW resonance. The SEW properties provide the SEW applicability in optical gas and biosensors. Similarly plasmon waveguides, one-dimensional photonic crystals are also considered as possible candidates for use in the two-dimensional integrated optical devices. Two-dimensional circuitry is suggested to control the SEW propagation by fabricating planar polymer elements such as lenses and waveguides, at thephotonic crystal surface.

Considering the SEW as a dielectric analogue of surface plasmons, but with much greater mean free path length in the spectral range corresponding to "window of transparency" of living cells, it can be expected that the use of the SEW will allow the effective optical trapping of cells and control their movement and spatial position.

         One of the important task is monitoring and control the SEW propagation using external   variable factors. A common way to monitor the status of optoelectronic systems is an external magnetic field application. The magneto-optical effects, such as the Faraday effect and Kerr appearing if magnetic field is applied can change the state of polarization of light propagating in the system. The specially designed microstructures, such as optical lattice or magnetophotonic crystals can significantly increase the magneto-optical effects. Magnetophotonic crystals are periodic dielectric structures composed of alternating layers of magnetic and non-magnetic material. Recently it was shown that in magnetophotonic crystals the SEW can be excited. A significant increase in the Faraday effect was also demonstrated in the vicinity of the resonance of surface states of photonic crystal. Taking into account the sensitivity of the SEW to the incident-light polarization, it can be expected that in magnetophotonic crystals the SEW may be controlled by an external magnetic field.

Observation of the magneto-optical properties of SEW in magnetophotonic crystals and magneto-optical switching of the PEV will be performed by the reflectance spectroscopy of magnetophotonic crystals in the geometry of attenuated total internal reflection in the Kretschmann scheme. Direct and alternating magnets will be used to create an external magnetic field with the strength of 1kOe.

The proposal includes the following main tasks:

- Numerical study of the Faraday rotation effect in magnetophotonic crystals will be performed in the vicinity of the SEW resonances depending on the crystal structure, the number of layers and the thickness of the last layer at the air / photonic crystal interface. Spectral and angular dependences of the magnetophotonic crystals reflectance for s- and p-polarizations of the incident radiation on the crystal will be calculated in the presence and absence of an external magnetic field by the transfer matrix technique. The effect of switching and control SEW excitation by an external magnetic field will be demonstrated.

- Experimental samples of one-dimensional magnetophotonic crystals will be designed, produced and optimizing for the most effectively SEW excitation and switching by the external magnetic field. The optical transmittance and reflectance spectroscopy in the Kretschmann scheme will be used for the characterization of the experimental samples and observing the spectral position of the resonance SEW. There will be a series of measurements of the polarization of the reflected light Faraday rotation angle close to the SEW resonance. Spectral-angular dependences of the reflectance of magnetophotonic crystals will be obtained using the reflectance spectroscopy technique with and without external magnetic field so the magneto-otpical switching of the SEW in magnetophotonic crystal will be observed.

5c) A sensor of external AC and DC magnetic field based on magnetoplasmonic crystals

(Victor Belyev; Team leader: Valeria Rodionova)

Continuous improvements in nanofabrication and nanocharacterization capabilities have changed predictions about the role of the metals in the development of optical devices and opened new perspectives in combination of different sensor techniques.

Small values of magneto-optical (MO) effects strongly restrict their practical applications and in the recent years several topics of photonic researches were targeted on the development of new types of small and reliable MO-devices such as biosensors, optical nanoantennas and hybrid ultrafast nanophotonic devices for the future telecommunications and data-recording. Sensitivity of the MO sensors can be enhanced by creating them on the basis of the magnetoplasmonic crystals which allow to enhance the MO Faraday or Kerr effects by excitation of surface plasmon-polaritons. Magnetoplasmonic nanostructures represent a special class of the plasmonic nanostructures fabricated from combination of noble (silver, gold) and magnetic metals (nickel, cobalt, iron or magnetic alloys). In such systems it is possible both to enhance the MO activity of the system via the surface plasmon excitation, and to modulate the plasmon properties via the application of magnetic field.

Our work is focused on investigation and comparison of magnetic, micromagnetic, optical and magneto-optical properties of Magnetoplasmonic crystals (MPlCs) based on diffraction gratings for designing a sensor of external AC and DC magnetic field. A prototype of MPlC-based sensor of AC and DC external magnetic field with sensitivity of 10-3 Oe was already developed. Theoretical calculations predict the possible increase of sensitivity up to 10-7 Oe. MPlC-based magnetic field sensor can be used as a probe for monitoring weak magnetic fields with high spatial - smallest region is about 100 um2, and time resolution is limited only by time of magnetization processes in ferromagnetic layer and has an order of nanoseconds. Now we are searching the ways for achieving the theoretical sensitivity and development of theoretical model, which will connect magnetic and magneto-optical properties of MPlCs.

Fabrication of MPlCs and investigation of their properties are carried out in collaboration with A. A. Fedyanin (Laboratory of nanophotonics and metamaterials, Lomonosov Moscow State University, Moscow, Russia); H. Takagi (Spin electronics group, Toyohashi University of Technology, Toyohashi, Japan); H. Munekata (Munekata research group, Tokyo Institute of Technologies, Tokyo, Japan) and A. Ognev (Laboratory of thin films technologies, Far East Federal University, Vladivostok, Russia).