Sergey V. Muraviov

In situ monitoring of laser modification process in human cataractous lens and porcine cornea using coherence tomography

We demonstrate that optical coherence tomography (OCT) is a convenient diagnostic tool to monitor pulse-to-pulse kinetics in laser interactions with biological tissue. In experiments on laser modification and ablation of the cataractous human lens and the porcine cornea we have applied this technique in situ to investigate different modes of preablation tissue swelling, crater formation and thermally affected zone development. The cataractous lens is an example of highly scattering media whereas the cornea is initially low scattering. The radiation with different wavelengths has been employed including that of a YAG:Er laser (λ=2.94 μm), a glass:Er laser (λ=1.54 μm), YAG:Nd lasers (λ=1.32 μm and λ=1.44 μm), as well as of the fifth harmonic of a Nd:YAP laser (λ=0.216 μm). Pulse-to-pulse OCT monitoring has been accompanied by the probe beam shielding diagnostics to provide the time-resolved observation of the interaction dynamics.

UV laser modifications and etching of polymer films (PMMA) below the ablation threshold

The modification of thin polymethylmethacrylate (PMMA) films by the fifth harmonic (λ=216 nm) of a Nd:YAP laser is studied. This modification manifests itself in essential changes of optical properties, film thickness (bulk etching) and solubility in appropriate developers (crosslinking). The modification kinetics is investigated for films of different thickness, for different laser fluences (below ablation threshold), in air, and in vacuum. The nonreciprocal response not connected with laser heating has been obtained.

Generation of Optical Soliton Pulses Smoothly Tunable in a Wide Frequency Range in Silica Fibers with Variable Dispersion

The possibility of the efficient conversion of the frequency of an optical soliton pulse in fibers with length-variable dispersion is physically analyzed and experimentally investigated. The effect is based on the Raman transformation of the frequency of an ultrashort pulse, which can be varied with high efficiency due to the compression mechanism of maintaining a high intensity of the pulse in a medium with monotonically decreasing anomalous dispersion. A smooth rearrangement of the spectrum of the soliton pulse 90 fs in duration in the range 1.58–1.75 μm is demonstrated.

Wavelength-tunable few-cycle optical pulses directly from an all-fiber Er-doped laser setup

A simple design, which we believe to be the first of its kind, of an all-fiber-based optical source is proposed for the generation of widely tunable few-cycle pulses as short as 20-25 fs duration in the range of 1.6-2.1 microm. Few-cycle pulses are obtained by compression of femtosecond pulses from the erbium-doped fiber laser in a three-stage scheme that uses (i) the effects of the soliton compression and the Raman frequency tuning in the dispersion decreasing fiber, as well as (ii) supercontinuum generation in a high-nonlinear silica fiber, and (iii) subsequent compression in a short conventional fiber.

VUV laser ablation of polymers: Photochemical aspect

A photochemical theory of laser ablation owing to the direct chain scission process is considered in quite general form taking into account the modification of material. The formulas obtained can be used for estimating mechanisms of VUV laser ablation of polymers.

Kinetics of low-scattering biotissue photodenaturation induced by the UV harmonics of a Nd:YAP laser and by Nd:YAG laser at a wavelength of 1440 nm

We study the effect of laser radiation on initially low scattering media such as egg white and crystalline substance. These media become highly scattering under laser irradiation. We perform and discuss three kinds of experiments, which elucidate the time dynamics of scattering of probe radiation. In the experiment of the first kind we investigate the pure photothermal denaturation of tissues under the effect of a Nd:YAG laser at a wavelength of 1440 nm (absorption coefficient in water is 26 cm-1). The theoretical model is derived which enables us to estimate the temperature rise involved. It also allow us to estimate the corresponding kinetics parameters of photodenaturation and characteristics of probe light scattering. In the experiment of the second kind we perform multiple pulse irradiation of tissues by UV harmonics (the fourth and the fifth) of a Nd:YAP laser with the aim to determine the characteristics of pure photochemical modification of materials. In these experiments the fluences were small enough to prevent heating of the materials. The results of the above experiments both of the first and the second kind allow us to estimate the relative contributions of photochemical modification of a tissue and photothermal protein denaturation within the experiments of the third kind, in which we use the mentioned above UV solid state laser harmonics at fluences high enough to produce heating of the materials.

UV-laser modifications and etching of thin polymer films in different environments

The role of environment in modification and etching of polymethylmethacrylate (PMMA) films by the fifth harmonic of Nd laser is investigated experimentally. The theoretical model is developed, which describes the main features of modification and etching kinetics for sufficiently small laser fluences.

Thermal diffusion in chalcogenide glass irradiated by a train of femtosecond laser pulses

Local heating of chalcogenide glass sample by a train of high-intensity femtosecond laser pulses depending on non-linear and thermal properties of the glass is studied in a theoretical model and in experiments on photo-induced glass modification.

Non-linear chalcogenide glasses and technologies for the development of ultra-fast chip-scale optical devices

Chalcogenide glasses are novel highly non-linear materials for photonics. Modification of optical glasses by high-intensity femtosecond pulses is a novel fast developing technology based on non-linear effects. In this paper, the advantages of using the method of femtosecond modifications for the fabrication of highly non-linear 3D photonic structures in bulk chalcogenide glasses are overviewed. Design and modelling of chip-scale highly non-linear structures for all-optical signal processing are discussed.

Formation of 3D dielectric structures by initiating polymerization with the fourth harmonic of an Nd laser

We studied the process of formation of 3D polymer structures by initiating polymerization with laser radiation. Polymers based on such monomers as methyl methacrylate and ethyleneglycolmonomethacrylate were investigated. Polymerization was initiated by the fourth harmonic radiation of a Q-switched Nd:YAP laser without any specially introduced initiator. Initiation is provided by the direct photolysis of monomers. At this wavelength the absorption of monomers is significantly higher than the absorption of corresponding polymer. It results in bleaching of the media during polymerization.