P. G. Kryukov

Inscription of fiber Bragg gratings by ultraviolet femtosecond radiation

We report on what is to our knowledge the first fabrication of fiber Bragg gratings by UV femtosecond radiation. The Bragg gratings, with photoinduced refractive-index modulation up to 1.92 x 10(-3) in H2-loaded SMF-28 and up to 1.05 x 10(-3) in Nufern GF1 fibers, were written by high-intensity (31-77-GW/cm2) femtosecond pulses at 264 nm. The dependence of the refractive-index modulation on intensity at equal fluences points to a two-photon absorption mechanism for grating inscription.

Fabrication of fiber Bragg gratings with 267 nm femtosecond radiation

Strong high-quality fiber Bragg gratings with photoinduced refractive-index modulation of more than 10-(3) were written in a Corning SMF-28 fiber, a P(2)O5-doped-core fiber and a pure-silica-core fluorine-doped-cladding fiber by third-harmonic radiation (267 nm, 150 fs and 1.2-1.8x1011 W/cm(2)) of a femtosecond Ti:sapphire laser using a phase mask. We compare the 267-nm photosensitivity responses with the results of irradiation by 193-nm ArF and 157-nm F(2) excimer lasers. The dependence of the refractive-index change on the exposure dose and the annealing characteristics of the fabricated gratings are typical for Type-I UV-written fiber gratings.

MECHANISM OF HIGH POWER PICOSECOND LASER UV INACTIVATION OF VIRUSES AND BACTERIAL PLASMIDS

Abstract— The mechanism of inactivating action of high‐power picosecond laser UV radiation (λ= 266 nm) on the λ and φX174 bacteriophages and the pBR 322 plasmid has been studied. It has been shown that at UV radiation intensities from 1011 to 1013 W/m2, inactivation of viruses and bacterial plasmids occurs mainly on account of single‐strand breaks in the DNA chain unlike the case of less powerful UV radiation where the inactivation is associated with the formation of pyrimidine dimers.

Mode-locked Bi-doped fiber laser

Mode locking is obtained for what we believe to be the first time in a Bi-doped fiber laser. Stable 50 ps laser pulses with a pulse repetition rate of 13 MHz are generated at a wavelength of 1161.6 nm with a 2 mW average power.

Inscription of long-period fiber gratings by femtosecond UV radiation

Using a new automated set-up and high-intensity 264 nm radiation, we record long-period fiber gratings with strong attenuation peaks in different fibers. The effects of laser inteisty and/or fluence in both H2-loaded and H2-outdiffused fibers aer investigated.

Femtosecond Er3+ Fiber Laser for Application in an Optical Clock

The main elements needed for the realization of a compact femtosecond methane optical clock are developed and studied. A femtosecond laser system on an Er3+ fiber (λ = 1.55 μm) contains an oscillator, an amplifier, and a fiber with a relatively high nonlinearity in which the supercontinuum radiation is generated in the range 1–2 μm. In the supercontinuum spectrum, the fragments separated by an interval that is close to the methane-optical reference frequency (λ = 3.39 μm) exhibit an increase in intensity. The supercontinuum radiation is converted into the difference frequency in a nonlinear crystal to the range of the methane-reference frequency (λ = 3.3–3.5 μm), so that the frequency components of the transformed spectrum have sufficient intensities for the subsequent frequency-phase stabilization with respect to the methane reference. A system that stabilizes the pulse repetition rate of the femtosecond Er3+ laser is also employed. Thus, the repetition rate of the ultrashort pulses of the femtosecond fiber laser is locked to the methane reference. The pulse repetition rate is compared with the standard second. Thus, the scheme of an optical clock is realized.

Picosecond pulse compression by means of soliton effects in single-mode silica glass fiber in the 2 μm spectral range

We report on the soliton-effect compression dynamics in single-mode SMF-28 fiber of picosecond pulses generated by an all-fiber MOPA-source based on a mode-locked thulium-doped fiber oscillator with an all-fiber dispersion management and a two-stage thulium and ytterbium co-doped watt-level amplifier. Initial 5-ps-long pulses were compressed down to 314 fs after having been amplified up to 1.4 W average power, giving an almost 16 compression factor (Some figures may appear in colour only in the online journal)

Experimental investigation of chemical oxygen-iodine laser

Results of an experimental investigation of a chemical oxygen-iodine laser (COIL) are presented. We determine the factors influencing the efficiency of a chemical singlet-oxygen generator (SOG) of the bubbler type operating on the chlorination of an alkaline solution of oxygen peroxide. We describe SOG constructions. A cw COIL with output power up to 400 W is developed on the basis of the investigated SOG. The feasibility of a modular construction of high-power COIL is demonstrated. A power-output level of 1 kW was achieved with a two-section laser. The feasibility is analyzed of COIL operation in a pulsed regime by pulsed bulk accrual of iodine atoms. We show that in this regime the laser can be operated without a low-temperature trap. An advantage of such a regime is also the possibility of controlling, in a wide range, the lasing pulse duration. A strong influence of molecular chlorine on the energy content of the active medium is observed when alkyliodides are used as iodine donors. The possibilities of using a pulsed COIL for controlled thermonuclear fusion are discussed.

A frequency-doubled pulsed chemical oxygen-iodine laser

The intracavity second-harmonic generation of pulsed chemical oxygen-iodine laser radiation was investigated. A pulsed chemical oxygen-iodine laser with a maximum output energy of 6.14 mJ was used. The second-harmonic output of 0.5 mJ was demonstrated using a lithium iodate crystal. The conversion efficiency of 8% was limited by intracavity losses. Numerical simulation predicts that a conversion efficiency of 75% can be obtained with 1% intracavity losses.

High-Power UV Ultrashort Laser Action on DNA and Its Components

Our studies in high-power laser UV action on DNA and its components were stimulated by interest shown in realization of selective action on complex biomolecules. In the very first experiments [1,2] on irradiating the aqueous solutions of nucleic acid bases by high-power laser UV radiation (I = 109 w/cm2, λ = 266 nm, τp = 30 ps) we revealed that such an action was characterized by irreversible decrease of absorption in the first electronic band, the decrease of absorption observed being proportional to the squared intensity. This points to a two - step character of the excitation process, and both the first singlet S1 state and the first triplet T1 state can be served as its intermediate state. When absorbing successively two UV quanta the molecule under irradiation acquires energy ~ 9.3 ev that exceeds the ionization limit. As a result, some photoproducts are formed which qualitatively differ from those formed by ordinary low-intensity UV irradiation [2].