Alexander Goltsov

Real-time detection of bacterial spores using coherent anti-Stokes Raman spectroscopy

We demonstrate a realistic method for detection of anthrax-type spores in real time based on their chemical fingerprints using coherent anti-Stokes Raman scattering. Specifically, we demonstrate that coherent Raman scattering can be used to successfully identify spores with high accuracy and high selectivity in less than 50ms.

Printable planar lightwave circuits with a high refractive index

We report a novel nanofabrication method to fabricate printable integrated circuits with a high refractive index working in the visible wavelength range. The printable planar ligthwave circuits are directly imprinted by ultra-violet nanoimprinting into functional TiO2-based resist on the top of planar waveguide core films. The printed photonic circuits are composed of several elementary components including ridge waveguides, light splitters and digital planar holograms. Multi-mode ridge waveguides with propagation losses around 40 dB cm(-1) at 660 nm wavelength, and, on-chip demultiplexers operated in the visible range with 100 channels and a spectral channel spacing around 0.35 nm are successfully demonstrated.

Concentration dependence in coherent Raman scattering

We investigate the concentration dependence of the femtosecond coherent anti-stokes Raman scattering (CARS) signals collected from several mixtures of molecules. We demonstrate a clear quadratic dependence of the transmitted CARS signal on the number of molecules of pyridine in water by looking at the Raman signal at 1030 cm−1. Using a backscattering configuration we study the quadratic concentration dependence in solid mixtures of dipicolinic acid, calcite, and gypsum in powder form.

Step-and-repeat nanoimprint on pre-spin coated film for the fabrication of integrated optical devices

Abstract. A step-and-repeat nanoimprint lithography (SR-NIL) process on a pre-spin-coated film is employed for the fabrication of an integrated optical device for on-chip spectroscopy. The complex device geometry has a footprint of about 3  cm2 and comprises several integrated optical components with different pattern size and density. Here, a new resist formulation for SR-NIL was tested for the first time and proved effective at dramatically reducing the occurrence of systematic defects due to film dewetting, trapped bubbles, and resist peel-off. A batch of 180 dies were imprinted, and statistics on the imprint success rate is discussed. Devices were optically characterized and benchmarked to an identical chip that was fabricated by electron-beam lithography. The overall performance of the imprinted nanospectrometers is well-aligned with that of the reference chip, which demonstrates the great potential of our SR-NIL for the low-cost manufacturing of integrated optical devices.

Very compact soft x-ray lasers and their potential applications

The results of two different series of experiments on generation lasing action in the soft x-ray region are presented. In the first series lasing in hydrogen-like Li III ions at 13.5 nm (2-1 transition to ground state) in a 5 mm long LiF microcapillary at 2 Hz repetition rate is demonstrated. The initial plasma was created in a 0. 3 mm diameter microcapillary by a low power Nd:YAG laser (0. 1 J in 5 ns), whereas the plasma pumping was proceeded with a 50 mJ, 250 fs UV laser. In the second series lasing is demonstrated in hydrogen-like B V ions at 26.2 nm (3-2 transition) using a very small Nd:YAG pumping laser (0.45 J in 8 ns) at a repetition rate of I Hz. The preplasma in a B 2 O 3 microcapillary was created from wall ablation with a 0.2 J (20 ns) KrF laser, and the whole soft x-ray lasing system takes up less space than is available on a 1.2 m × 3 m optical table. In the last part of the paper the development of soft-x-ray lasers (SXLs) for application in lithography and soft x-ray microscopy is discussed.

Fabrication of digital planar holograms into high refractive index waveguide core for spectroscopy-on-chip applications

A novel class of large-bandwidth wavelength demultiplexers, based on digital planar holography for on-chip spectroscopy applications, was fabricated in high refractive index contrast SiO2/Si3N4 planar waveguides. The devices consist of computer-generated digital planar holograms (DPHs) encoding the transfer function of the demultiplexers, engraved on the core layer of the optical waveguide. An optimized fabrication process has been developed to produce DPHs with an etching depth as low as 10 nm in Si3N4. The first spectrometer devices exhibit overall bandwidths as large as 98 nm and spectral channel spacings down to 0.3 nm/channel.

Digital planar holography and multiplexer/demultiplexer with discrete dispersion

Digital Planar Holography (DPH) has arrived due to progress in microlithography, planar waveguide fabrication, and theoretical physics. A computer-generated hologram can be written by microlithography means on the surface of a planar waveguide. DPH combines flexibility of digital holograms, superposition property of volume (thick) holograms, and convenience of microlithographic mass production. DPH is a powerful passive light processor, and could be used to connect multiple optical devices in planar lightwave circuits (PLCs), and if combined with active elements on the same chip, may perform not only analog operations but also logical ones. A DPH implementation of a multiplexer/demultiplexer with discrete dispersion is proposed and demonstrated, avoiding communication signal distortion inherent in multiplexers/demultiplexers with continuous dispersion. The concept of discrete dispersion leads to a device with a flat top transfer function without a loss penalty. The dispersion is created with custom-designed bandgaps for specific directions. A DPH hologram resembles a poly-crystal with long-range correlations, and it exhibits the properties of a quasi-crystal. Unlike photonic crystals, light in quasi-crystal may propagate in almost any direction. Single mode planar waveguides are specially designed to suppress parasitic reflections that appear due to mixture of TE-modes, TM-modes, and cladding modes. Demultiplexers with 2-32 channels were demonstrated on planar waveguides with binary single-layer lithography.

Real-time blood analysis using Coherent Anti-Stokes Raman Scattering

We demonstrate a real-time method of blood analysis. Using a novel coherent Raman technique we record the vibrational spectrum from picoliters of whole blood in milliseconds. This method will allow real-time, in vivo, blood monitoring.

Photonic bandgap quasi-crystals for integrated WDM devices

A novel concept of Photonic Bandgap Quasi-Crystal (PBQC) as a platform for planar integrated WDM optical devices is proposed. The PBQC can be lithographically fabricated in a planar waveguide as a computer-generated two-dimensional hologram. In this approach the spectral selectivity of Bragg gratings, focusing properties of elliptical mirrors, superposition properties of thick holograms, photonic bandgaps of periodic structures, and flexibility of lithography on planar waveguides are combined. In distinction to conventional combination of independent planar Bragg gratings, in PBQC we create multiple bandgaps by synthesizing a synergetic super-grating of a number of individual sub-gratings. The device spectral selectivity is determined by those of the sub-gratings. The super-grating comprises million(s) of dashes etched on an interface of a planar waveguide. Each dash is a binary feature placed by a computer program to serve simultaneously many channels. For realization of PBQC devices the software for generating super-gratings (GDS-II format) and 2-D simulation of its transfer function was developed. Direct e-beam writing and photolithography were used for manufacturing PBQC structures. For verification of the ideas behind the concept a number of multichannel MUX/DEMUX devices have been manufactured and experimentally tested. The results of detailed experimental study of 4- and 16-channel devices will be presented. Channel isolation ~30 dB was achieved in the 4-channel devices. The applications of PBQC platform for integrated light wave circuits are discussed.

Digital planar holograms fabricated by step and repeat UV nanoimprint lithography: From spectrometer chip to higher power laser diodes

The fabrication of digital planar holograms by Step and Repeat UV nanoimprint lithography is reported. It opens a route for commercial development of new nanophotonic devices based on digital planar holography. Two first applications to be demonstrated are the high resolution spectrometer chips and the enhancement of brightness and power of laser diodes.