Svetlana Zolotovskaya

Coherent control of plasmonic nanoantennas using optical eigenmodes

The last decade has seen subwavelength focusing of the electromagnetic field in the proximity of nanoplasmonic structures with various designs. However, a shared issue is the spatial confinement of the field, which is mostly inflexible and limited to fixed locations determined by the geometry of the nanostructures, which hampers many applications. Here, we coherently address numerically and experimentally single and multiple plasmonic nanostructures chosen from a given array, resorting to the principle of optical eigenmodes. By decomposing the light field into optical eigenmodes, specifically tailored to the nanostructure, we create a subwavelength, selective and dynamic control of the incident light. The coherent control of plasmonic nanoantennas using this approach shows an almost zero crosstalk. This approach is applicable even in the presence of large transmission aberrations, such as present in holographic diffusers and multimode fibres. The method presents a paradigm shift for the addressing of plasmonic nanostructures by light.

Infrared laser pulse triggers increased singlet oxygen production in tumour cells

Photodynamic therapy (PDT) is a technique developed to treat the ever-increasing global incidence of cancer. This technique utilises singlet oxygen (1O2) generation via a laser excited photosensitiser (PS) to kill cancer cells. However, prolonged sensitivity to intensive light (6–8 weeks for lung cancer), relatively low tissue penetration by activating light (630 nm up to 4 mm), and the cost of PS administration can limit progressive PDT applications. The development of quantum-dot laser diodes emitting in the highest absorption region (1268 nm) of triplet oxygen (3O2) presents the possibility of inducing apoptosis in tumour cells through direct 3O2 → 1O2 transition. Here we demonstrate that a single laser pulse triggers dose-dependent 1O2 generation in both normal keratinocytes and tumour cells and show that tumour cells yield the highest 1O2 far beyond the initial laser pulse exposure. Our modelling and experimental results support the development of direct infrared (IR) laser-induced tumour treatment as a promising approach in tumour PDT.

Generation of propagation-invariant light beams from semiconductor light sources

We have studied the possibility of generating propagation-invariant (nondiffracting) light beams using various semiconductor sources of radiation. The propagation-invariant (Bessel) beams have been generated using cone-shaped lenses (axicones) with an apical angle of 178° and 170°, which provided beams with a central spot diameter of 100 and 10 μm, respectively. The radiation sources were represented by various types of light-emitting diodes, quasi-single-mode semiconductor vertical-cavity surface-emitting lasers and broad-stripe (100 μm) edge-emitting laser diodes. It is demonstrated that these semiconductor light sources offer a promising basis for the generation of propagation-invariant light beams in various devices (including optical tweezers) intended for manipulating micro- and nanodimensional objects.

Two-Color Output From InGaAs Laser With Multiplexed Reflective Bragg Mirror

An optical scheme for stable two-color operation from a single laser diode (LD) by means of a multiplexed reflective Bragg mirror is proposed and demonstrated. A mode spectral separation of ~ 3 nm (1 THz) and laser linewidth less than 80 pm, with sidemode suppression ratio over 24 dB, and an output power of 1.7 W are achieved with a monolithic dual-wavelength Bragg mirror. Temperature stability of spectral locking of an LD in dual-wavelength operation is presented.

Low secondary electron yield engineered surface for electron cloud mitigation

Secondary electron yield (SEY or δ) limits the performance of a number of devices. Particularly, in high-energy charged particle accelerators, the beam-induced electron multipacting is one of the main sources of electron cloud (e-cloud) build up on the beam path; in radio frequency wave guides, the electron multipacting limits their lifetime and causes power loss; and in detectors, the secondary electrons define the signal background and reduce the sensitivity. The best solution would be a material with a low SEY coating and for many applications δ < 1 would be sufficient. We report on an alternative surface preparation to the ones that are currently advocated. Three commonly used materials in accelerator vacuum chambers (stainless steel, copper, and aluminium) were laser processed to create a highly regular surface topography. It is shown that this treatment reduces the SEY of the copper, aluminium, and stainless steel from δmax of 1.90, 2.55, and 2.25 to 1.12, 1.45, and 1.12, respectively. The δmax furt...

Nonlinear properties of phototropic media on the basis of CuxSe nanoparticles in quartz glass

Energy and kinetic characteristics of theinduced transparency in quartz sol-gel glasses containing copper selenide nanoparticles of different stoichiometry are studied. The dependence of the nonlinear optical properties of the glass samples on the chemical composition of copper selenide particles, which gives rise to an additional absorption band in the near-infrared region and determines its spectral position, is established. It is found that the time of relaxation of the induced transparency increases and the peak absorption cross section decreases as the absorption maximum shifts to the low-energy spectral region.

Nonredundant Raman imaging using optical eigenmodes

Various forms of imaging schemes have emerged over the last decade that are based on correlating variations in incident illuminating light fields to the outputs of single “bucket” detectors. However, to date, the role of the orthogonality of the illumination fields has largely been overlooked, and, furthermore, the field has not progressed beyond bright field imaging. By exploiting the concept of orthogonal illuminating fields, we demonstrate the application of optical eigenmodes (OEis) to wide-field, scan-free spontaneous Raman imaging, which is notoriously slow in wide-field mode. The OEi approach enables a form of indirect imaging that exploits both phase and amplitude in image reconstruction. The use of orthogonality enables us to nonredundantly illuminate the sample and, in particular, use a subset of illuminating modes to obtain the majority of information from the sample, thus minimizing any photobleaching or damage of the sample. The crucial incorporation of phase, in addition to amplitude, in the imaging process significantly reduces background noise and results in an improved signal-to-noise ratio for the image while reducing the number of illuminations. As an example we can reconstruct images of a surface-enhanced Raman spectroscopy sample with approximately an order of magnitude fewer acquisitions. This generic approach may readily be applied to other imaging modalities such as fluorescence microscopy or nonlinear vibrational microscopy.

Study of non-diffracting light beams from broad-stripe edge-emitting semiconductor lasers

Broad-stripe edge-emitting semiconductor lasers have been used to obtain propagation-invariant (nondiffracting) light beams with powers and diameters of the central ray acceptable for optical manipulation and tweezing. The results of investigations of the propagation of Bessel beams generated from broad-stripe lasers with spectrally selective resonator show that the spatial homogeneity of emission plays a much greater role than the temporal coherence in the formation of Bessel beams. The main factors limiting the length of non-diffracting beam propagation (without distortion of the central ray) are the astigmatism and multimode character of laser radiation.

Diode-pumped Yb,Er:glass laser passively Q switched with a V3+:YAG crystal

Saturable-absorber Q switching of a diode-pumped erbium-doped glass laser at 1.54 microm with a V:YAG crystal has been demonstrated. An average output power of 30 mW with Q-switching efficiency of 37% and pulse duration of 350 ns have been obtained. Results of the numerical simulation of the laser have been presented.

Electronically Controlled Pulse Duration Passively Mode-Locked Cr : Forsterite Laser

A passive mode-locked Cr:forsterite laser with electronically controlled pulse duration is demonstrated. A DC voltage controlled p-n junction quantum-dot semiconductor saturable absorber mirror is presented. Output pulse durations varying from 17.4 to 6.4 ps were obtained by applying a DC voltage between 0 and -4.5 V. No dispersion compensation was used.