Modeling of phase volume diffractive gratings, part 1: transmitting sinusoidal uniform gratings

A detailed model of the diffraction of plane and Gaussian beams on plane uniform phase Bragg gratings based on Kogelnik\u27s theory of coupled waves is presented. The model describes transmitting gratings with arbitrary orientation in a plane-parallel plate taking into account spectral width and angular divergence of laser beams along with material dispersion of a photosensitive medium. The model results are compared with experimental data for high- efficiency Bragg gratings in a photothermorefractive (PTR) glass

Intrinsic laser-induced breakdown of silicate glasses

This paper is a survey of experimental results in laser-induced damage observed mainly at State Optical Institute (St. Petersburg, Russia) and at School of Optics/CREOL (Orlando, FL) which expounds conditions of observation of an intrinsic breakdown of high-purity silicate glasses and proposes the general idea of its mechanism. It is shown that the surface laser-induced breakdown of dielectrics is resulted from photo- and thermo-ionization of surface defects but not from interaction of laser radiation with dielectric material itself. Conditions of thermal ionization of the volume of dielectric materials are determined in dependence on features of absorption of material and temporal features of laser radiation. Statistical properties of laser-induced breakdown of high-purity glasses are caused by statistical properties of laser radiation while the breakdown itself is a deterministic process. Elimination of impact of self-focusing on the results of the breakdown threshold measurements is observed if the spot size of laser radiation in focal plane is less than the wavelength. No photoionization of glass matrix is detected before laser-induced breakdown, and there is no effect of photoionization of impurities and defects on intrinsic breakdown. A mechanism of intrinsic laser-induced breakdown is proposed which is a spasmodic transformation of the electronic level structure in a wide-bandgap dielectric caused by the electric field of laser radiation. This is a collective process converting a transparent material to the opaque state but not an individual process of any type of ionization

Optical absorption and ionization of silicate glasses

Intrinsic, extrinsic (transition metals and hydroxyl), and induced (color centers) absorption of multicomponent silicate glasses in UV, visible and near JR spectral regions are described. Parasitic effects influencing absorption measurements are discussed. Excitation to the intrinsic absorption band results in intrinsic luminescence and ionization followed by color center generation and phosphorescence. The thresholds of electron and hole mobility in glass network are found in the far UV region. The hole-centers generation as a criterion of substance ionization is proposed. A number of nonlinear mechanisms of glass ionization are discussed. Two-photon ionization was detected in alkaline-silicate glasses exposed to high-power laser radiation in nano- and picosecond regimes..Three-photon ionization was detected in lead-silicate glasses. No reliable data on multiphoton ionization (with number of photons more than 3) of glasses are found. Two- and three-photon cooperative self-multiplication of color centers was found in CuC1-doped glasses. Glass matrix ionization by spectral broadening of femtosecond JR pulses is described. Thermal and surface ionization of glass under intense irradiation by pulsed lasers is described. 1

Volume Holographic Elements In A Photo-Thermo-Refractive Glass

This paper is a survey of properties and applications of holographic optical elements in a photo- thermo-refractive (PTR) glass developed at Vavilov State Optical Institute (St. Petersburg, Russia) and the University of Central Florida. It is a glass in which Bragg gratings (holograms) can be written in the interior (not the surface) of the glass. Novel volume diffractive gratings have been made including exceptionally narrow band transmitting and reflecting elements. This technology is used to make diffractive elements such as spatial filters, attenuators, switches, modulators, beam splitters, beam samplers, beam deflectors, selectors of particular wavelengths (notch filters, add/drop elements), spectral shape formers (gain equalizers), spectral sensors, angular sensors, Bragg spectrometers, transverse and longitudinal mode selectors in a laser resonator, and wavelength tuners and stabilizers for different lasers. © 2009 American Scientific Publishers

Recording Of Robust Holographic Optical Elements In Glass

This is a survey of recent results achieved with an inorganic material for volume holographic optical elements which is more efficient and robust than alternative materials. It is a photo-thermo-refractive (PTR) glass in which Bragg gratings (holograms) can be written in the interior (not the surface) of the glass. PTR glass is transparent from 350 to 2700 nm. It is a crown-type optical glass having refractive index at 587.5 nm nd=1.4959 and Abbe number vd=59.2. This glass shows low dependence of refractive index on temperature dn/dt\u3c10-6 1/K. PTR glass has the same nonlinear refractive as fused silica. Refractive index in PTR glass decreases for 1000 ppm after UV exposure and thermal development. An approximate value of the photosensitivity is Δn/E=1.5×10-3 cm2/J. Laser damage threshold is 40 J/cm2 for 8 ns laser pulses at 1064 nm. Glass is stable in multi-kilowatt CW laser beams. Novel volume diffractive gratings have been made including exceptionally narrow band transmitting and reflecting elements. This technology is used to make diffractive elements such as spatial filters, attenuators, switches, modulators, beam splitters, beam samplers, beam deflectors, selectors of particular wavelengths (notch filters, add/drop elements), spectral shape formers (gain equalizers), spectral sensors, angular sensors, Bragg spectrometers, transverse and longitudinal mode selectors in a laser resonator, and wavelength tuners and stabilizers for different lasers. Combinations of the above listed elements can be made within the same piece of glass. High power semiconductor and solid state volume Bragg lasers oscillating in single transverse mode with spectral width below 50 pm are demonstrated

Fabrication And Applications Of Volume Bragg Gratings

Basics and last results in laser beam control by volume Bragg gratings recorded in photothermo-refractive glass based on their high efficiency, narrow spectral selectivity and high tolerance to high power laser radiation are presented. © 2009 Optical Society of America

Kinetics Modeling In Photosensitive Glass

Kinetics of photoinduced process is studied in a new photosensitive material for volume hologram recording which is a photo-thermo-refractive glass (PTRG). A system of balance equations is derived which describes the processes of generation of electrons in a conduction band of these glass matrix by photoionization of Ce3+ and trapping of electrons by both silver ions Ag+ and hole centers (Ce3+)+. The main approach for the system solution is a calculation of low quasistationary concentration of free electrons in a conduction band, while concentrations of generated electron and hole centers are expected to be variable. A general solution of a system is found as a combination of exponential and hyperbolic functions. It is shown that an exponential solution is the result of the absence of a re-trapping of electrons, while a pure hyperbolic solution occurs in the case of equal probability of trapping and re-trapping. The approach developed for the first stage of photo-thermo-refractive process which is photoionization and trapping, is applied for the modeling of the final result of the whole process of photo-thermo-induced refractive index transformation in glass. It is found that the refractive index increment in PTRG is better described by hyperbolic function compare to the exponential one. Kinetic parameters of induced refraction in PTRG are determined. © 2003 Published by Elsevier B.V

Photosensitive Holographic Glass - New Approach To Creation Of High Power Lasers

A photosensitive glass demonstrating refractive index decrement after exposure to UV radiation followed by thermal development is used for phase volume hologram recording. This photo-thermo-refractive (PTR) glass is a sodium zinc aluminium silicate glass doped with cerium, silver and fluorine. Spatial modulation of refractive index resulted from precipitation of nanocrystalline phase of sodium fluoride. Volume Bragg gratings recorded in this glass, show extremely narrow spectral and angular selectivity and have low losses combined with high tolerance to laser radiation. These gratings possess a unique ability to produce laser beam transformations directly in angular space. This feature paves a way to creation of high power semiconductor lasers with stable narrow emission spectra and diffraction limited divergence. This approach is based on three types of holographic optical elements made from PTR glass. They are an output coupler providing single transverse mode oscillation for broad area emitters, a phase coupling element providing coherent emission from a number of spatially separated lasers, and a spectral beam combiner summarising a number of laser beams with different wavelengths within a single beam with diffraction limited divergence

High Brightness Laser Design Based On Volume Bragg Gratings

This paper is a survey of recent achievements at the College of Optics and Photonics/CREOL at the University of Central Florida in the use of newly developed diffractive optical elements which are volume Bragg gratings recorded in a photo-thermo-refractive (PTR) glass. Three levels of semiconductor laser design are proposed to achieve high-power low-divergence output. The first level is the change of a mechanism of transverse mode selection from spatial selection by apertures to angular selection by PTR Bragg gratings. This approach allows increasing of aperture without increasing of length and selecting of arbitrary mode but not only a fundamental one. The second level is coherent coupling of emitters by means of PTR Bragg gratings which provide excitation of the only one common mode in a multichannel resonator. This type of phase locking automatically leads to a narrow spectral width of emission usually not exceeding a few tens of picometers. The third level is spectral beam combining by a stack of PTR Bragg gratings which re-direct radiation from several phase coupled arrays to the same direction within diffraction limited divergence. This approach allows simplifying of thermal management because the only passive device with low absorption (a PTR beam combiner) is placed in a high power laser beam

Volume Bragg Gratings For Spectral Beam Combining

Basics and last results in spectral beam combining by volume Bragg gratings recorded in photothermo-refractive glass based on their high efficiency, narrow spectral selectivity and high tolerance to high power laser radiation are presented. © 2009 Optical Society of America