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Despite the multitude of available methods, the characterization of ultrafast pulses remains a challenging endeavor, especially at the single-photon level. We introduce a pulse characterization scheme that maps the magnitude of its short-time Fourier transform. Contrary to many well-known solutions it does not require nonlinear effects and is therefore suitable for single-photon-level measurements. Our method is based on introducing a series of controlled time and frequency shifts, where the latter is performed via an electro-optic modulator allowing a fully-electronic experimental control. We characterized the full spectral and temporal width of a classical and single-photon-level pulse and successfully tested the applicability of the reconstruction algorithm of the spectral phase and amplitude. The method can be extended by implementing a phase-sensitive measurement and is naturally well-suited to partially-incoherent light.

Despite the multitude of available methods, the characterization of ultrafast pulses remains a challenging endeavor, especially at the single-photon level. We introduce a pulse characterization scheme that maps the magnitude of its short-time Fourier transform. Contrary to many well-known solutions it does not require nonlinear effects and is therefore suitable for single-photon-level measurements. Our method is based on introducing a series of controlled time and frequency shifts, where the latter is performed via an electro-optic modulator allowing a fully-electronic experimental control. We characterized the full spectral and temporal width of a classical and single-photon-level pulse and successfully tested the applicability of the reconstruction algorithm of the spectral phase and amplitude. The method can be extended by implementing a phase-sensitive measurement and is naturally well-suited to partially-incoherent light.

Results concerning the controllable ablation of nano-layered thin films (NLTF) by femtosecond laser pulses are presented. Investigated samples were titanium-aluminum bilayers, deposited on a silicon substrate, with the top titanium or aluminum layer of variable thickness on the surface. Irradiation was done in ambient air with single femtosecond laser pulses under standard laboratory conditions. The samples were analyzed by complementary methods of optical and scanning electron microscopy and optical profilometry, exhibiting laser-fluence-dependent ablative removal either of the top layer or the entire bilayer or even partial ablation of the underlying silicon substrate. The removal (spallation) threshold fluences for the topmost layer are scalable versus its thickness almost irrespectively of its material, being rather selective for the Ti-coated samples and much less selective for the Al-coated samples. The removal of the entire bilayers was found to be strongly influenced by electronic properties of the underlying metallic layer, dictating the NLTF-Si adhesion, heat conduction, and capacity in the NLTFs toward the NLTF-Si interface and beyond, as well as by their thermophysical characteristics, e.g., almost twice higher melting temperature and enthalpy for Ti. As a result, precise fs-laser machining of the entire NLTFs is pronounced and selective for the samples with the fusible Al at the low-adhesion Al-Si interfaces, compared with the incomplete NLTF removal from the high-adhesion and refractory Ti-Si interfaces.

A well-characterized wavefront is important for many x-ray free-electron laser (XFEL) experiments, especially for single-particle imaging (SPI), where individual biomolecules randomly sample a nanometer region of highly focused femtosecond pulses. We demonstrate high-resolution multiple-plane wavefront imaging of an ensemble of XFEL pulses, focused by Kirkpatrick–Baez mirrors, based on mixed-state ptychography, an approach letting us infer and reduce experimental sources of instability. From the recovered wavefront profiles, we show that while local photon fluence correction is crucial and possible for SPI, a small diversity of phase tilts likely has no impact. Our detailed characterization will aid interpretation of data from past and future SPI experiments and provides a basis for further improvements to experimental design and reconstruction algorithms.

A well-characterized wavefront is important for many x-ray free-electron laser (XFEL) experiments, especially for single-particle imaging (SPI), where individual biomolecules randomly sample a nanometer region of highly focused femtosecond pulses. We demonstrate high-resolution multiple-plane wavefront imaging of an ensemble of XFEL pulses, focused by Kirkpatrick–Baez mirrors, based on mixed-state ptychography, an approach letting us infer and reduce experimental sources of instability. From the recovered wavefront profiles, we show that while local photon fluence correction is crucial and possible for SPI, a small diversity of phase tilts likely has no impact. Our detailed characterization will aid interpretation of data from past and future SPI experiments and provides a basis for further improvements to experimental design and reconstruction algorithms.

A well-characterized wavefront is important for many x-ray free-electron laser (XFEL) experiments, especially for single-particle imaging (SPI), where individual biomolecules randomly sample a nanometer region of highly focused femtosecond pulses. We demonstrate high-resolution multiple-plane wavefront imaging of an ensemble of XFEL pulses, focused by Kirkpatrick–Baez mirrors, based on mixed-state ptychography, an approach letting us infer and reduce experimental sources of instability. From the recovered wavefront profiles, we show that while local photon fluence correction is crucial and possible for SPI, a small diversity of phase tilts likely has no impact. Our detailed characterization will aid interpretation of data from past and future SPI experiments and provides a basis for further improvements to experimental design and reconstruction algorithms.

A well-characterized wavefront is important for many x-ray free-electron laser (XFEL) experiments, especially for single-particle imaging (SPI), where individual biomolecules randomly sample a nanometer region of highly focused femtosecond pulses. We demonstrate high-resolution multiple-plane wavefront imaging of an ensemble of XFEL pulses, focused by Kirkpatrick–Baez mirrors, based on mixed-state ptychography, an approach letting us infer and reduce experimental sources of instability. From the recovered wavefront profiles, we show that while local photon fluence correction is crucial and possible for SPI, a small diversity of phase tilts likely has no impact. Our detailed characterization will aid interpretation of data from past and future SPI experiments and provides a basis for further improvements to experimental design and reconstruction algorithms.

A well-characterized wavefront is important for many x-ray free-electron laser (XFEL) experiments, especially for single-particle imaging (SPI), where individual biomolecules randomly sample a nanometer region of highly focused femtosecond pulses. We demonstrate high-resolution multiple-plane wavefront imaging of an ensemble of XFEL pulses, focused by Kirkpatrick–Baez mirrors, based on mixed-state ptychography, an approach letting us infer and reduce experimental sources of instability. From the recovered wavefront profiles, we show that while local photon fluence correction is crucial and possible for SPI, a small diversity of phase tilts likely has no impact. Our detailed characterization will aid interpretation of data from past and future SPI experiments and provides a basis for further improvements to experimental design and reconstruction algorithms.

The frequency doubling of femtosecond laser pulses in a two-dimensional (2D) rectangular nonlinear photonic lattice with hexagonal domains is studied experimentally and theoretically. The broad fundamental spectrum enables frequency conversion under nonlinear Bragg diffraction for a series of transverse orders at a fixed longitudinal quasi-phase-matching order. The consistent nonstationary theory of the frequency doubling of femtosecond laser pulses is developed using the representation based on the reciprocal lattice of the structure. The calculated spatial distribution of the second-harmonic spectral intensity agrees well with the experimental data. The condition for multiple nonlinear Bragg diffraction in a 2D nonlinear photonic lattice is offered. The hexagonal shape of the domains contributes to multibeam second harmonic excitation. The maximum conversion efficiency for a series of transverse orders in the range 0.01%-0.03% is obtained. © 2018 Astro Ltd.

Processing of AlTiN/TiN multilayered hard coatings by femtosecond (fs) laser pulses has been investigated. Irradiation was performed in air with linearly polarized laser radiation with pulses of 200 fs duration at 775 nm wavelength. Single or 1000 subsequent laser pulses were directed at normal incidence towards target surface. Laser energy per pulse was adjusted from 0.5 to 50 mu J and corresponding fluence was 0.17-17.5 J cm(-2). The as deposited and laser-ablated samples were characterized by optical confocal microscopy, optical profilometry and scanning and transmition electron microscopy. In case of the AlTiN/TiN coating, a single-pulse damage threshold of 0.41 J cm(-2) was estimated. Well defined holes/craters with diameters from 7 to 35 mu m, up to 40 mu m depth were drilled, depending on laser pulse energy and number, after 1000 laser pulses. For small energy/fluence, laser induced periodical surface structures were observed. A model is discussed which can account for these features by the accumulation effect during multi-pulse irradiation. The forming craters can prove useful for fabrication of micron solid state lubricant reservoirs in the protective coating-steel system.

Processing of AlTiN/TiN multilayered hard coatings by femtosecond (fs) laser pulses has been investigated. Irradiation was performed in air with linearly polarized laser radiation with pulses of 200 fs duration at 775 nm wavelength. Single or 1000 subsequent laser pulses were directed at normal incidence towards target surface. Laser energy per pulse was adjusted from 0.5 to 50 mu J and corresponding fluence was 0.17-17.5 J cm(-2). The as deposited and laser-ablated samples were characterized by optical confocal microscopy, optical profilometry and scanning and transmition electron microscopy. In case of the AlTiN/TiN coating, a single-pulse damage threshold of 0.41 J cm(-2) was estimated. Well defined holes/craters with diameters from 7 to 35 mu m, up to 40 mu m depth were drilled, depending on laser pulse energy and number, after 1000 laser pulses. For small energy/fluence, laser induced periodical surface structures were observed. A model is discussed which can account for these features by the accumulation effect during multi-pulse irradiation. The forming craters can prove useful for fabrication of micron solid state lubricant reservoirs in the protective coating-steel system.

Rapidly developing areas of high field physics, generation of high order harmonics or isolated attosecond pulses, require high peak power few-cycle pulse sources. Optical parametric chirped pulse amplification (OPCPA) has shown potential to satisfy these requirements and at present OPCPA is the leading technology for high energy few-cycle pulse table-top systems. The main objectives of this thesis were to investigate optical parametric amplification of broadband seed pulses in femtosecond and picosecond regimes, to develop and optimize a compact TW-scale OPCPA system intended for various applications in areas of high-field physics. In this thesis the main concept of such system is discussed, advantages and disadvantages of proposed approach are analyzed, the setup is compared to other world known systems. In this thesis an original approach for power scaling of regenerative amplifier by implementing several active elements in prolonged resonator has been proposed and investigated. Femtosecond pulse amplification in dual active element Yb:KGW regenerative amplifier has been demonstrated, resulting in boost of average output power to 30 W. Broad bandwidth pulse generation, parametric amplification and compression to transform limited values were analyzed both numerically and experimentally. White light continuum generation in bulk material for broadband seed formation, its further optical parametric amplification in noncollinear scheme were investigated and Yb:KGW driven... [to full text], Stiprių laukų fizikos srities tyrimams, aukštų eilių harmonikų ir pavienių atosekundinių impulsų generavimui, yra reikalingos kompaktiškos teravatų smailinės galios kelių optinių ciklų išvadinių impulsų lazerinės sistemos. Optinis parametrinis „čirpuotų“ impulsų stiprinimas yra vienas pagrindinių metodų leidžiančiu pasiekti šiems taikymams reikalingus lazerinių sistemų parametrus. Šios disertacijos darbo tikslas – ištirti femtosekundinės ir pikosekundinės trukmės impulsų stiprinimą optiniuose parametriniuose stiprintuvuose užkratui naudojant ypač plataus spektro signalą, bei sukurti ir optimizuoti čirpuotų impulsų parametrinio stiprinimo sistemą, užtikrinančią patikimą teravatų smailinės galios impulsų formavimą. Disertacijoje aptariama bendra tokios sistemos architektūra, nagrinėjami privalumai ir trūkumai, palyginama su kitomis pasaulyje egzistuojančiomis sistemomis. Šiame darbe pasiūlytas ir ištirtas lazerių vidutinės išvadinės galios didinimo metodas, naudojant kelis aktyviuosius elementus viename rezonatoriuje, ir pademonstruotas femtosekundinių impulsų stiprinimas šio metodo pagrindu sukonstruotame dviejų Yb:KGW aktyvių elementų regeneratyviniame stiprintuve, tokiu būdu padidinant lazerio išvadinę galią iki 30 W. Darbo metu sukonstruota bei ištirta Yb:KGW femtosekundiniu lazeriu kaupinamos baltos šviesos kontinuumo generavimo ir nekolinearaus kaupinimo optinio parametrinio stiprinimo sistema, kurios išvadinių impulsų energiją siekia 20 mikrodžiaulių, o impulsai... [toliau žr. visą tekstą]

В этой статье представлены результаты численных исследований распространения сверхмощного ультракороткого лазерного излучения. = This article presents the results of numerical studies of the spread of super-power ultrashort laser radiation.

The interplay of the various ionization mechanisms reveals itself through the dependence of breakdown events on laser parameters such as pulse duration, wavelength, and pulse energy. In the past, the dependence of the breakdown threshold on pulse duration has attracted most attention because of the lowering of the energy threshold with decreasing pulse duration that enables precise material processing. In the present study, these aspects are included because we use pulse durations ranging from approximately equal to 300 fs to approximately equal to 10 ns. However, we go far beyond by presenting a detailed analysis of the wavelength dependence of the breakdown thresholds for nanosecond and femtosecond breakdown, and of the dependence of energy deposition on laser pulse energy. These studies are performed with unprecedented wavelength and energy resolution. They reveal previously unknown features of the optical breakdown process, and enable to assess the possibilities of controlled nonlinear energy deposition in the entire wavelength-pulse duration parameter space., The original document contains color images.

The recent merge of precision optical frequency metrology and ultrafast laser technology has made a profound impact to a number of scientific disciplines, including fundamental physical tests, precision spectroscopy in chemistry, biology, and material science, metrological support in space science, and coherent quantum control. For the area of frequency metrology on which this proposal is focused, we expect a significant increase in the stability and accuracy of frequency standards is needed and is ready to be developed, especially in light with the identification of optically based transitions with extremely high quality factors. Phase coherent connection between the optical and microwave spectral regions has now been established with direct optical frequency synthesis, with a qualitatively new regime being developed owing to the introduction of precise femtosecond laser based optical frequency comb technology. At the present time, optical fiber communication lines (OFCL) are widely used. One way for increasing the OFCL transmission capacity is the spectral separation of channels. For this, a stable chain of working optical frequencies is necessary. It is convenient to use the radiation from a stabilized femtosecond laser as such a frequency chain. The prospects for using such femtosecond synthesizers for OFCL are confirmed by the fact that there are many publications on this theme. .In first stage we propose to develop an ideal alternative system based on femtosecond diode-pumped ytterbium-laser. The use of diode pumping for crystalline lasers makes it possible to construct compact, highly efficient, as well as economical laser systems. The relatively low thermal load and compactness of the laser system help to create stable optical resonators and to obtain highly reliable laser operating parameters. A femtosecond comb system based on a Yb-laser will be much more compact and economical than its Ti:S counterpart., The original document contains color images.

We overview and summarize the progress of the spectral phase encoded time spreading (SPECTS) optical code division multiple access (O-CDMA) technology. Recent progress included a demonstration of a 320 Gbit/s (32-user x 10 Gbit/s) all-optical passive optical network testbed based on the SPECTS O-CDMA technology and a theoretical prediction of the spectral efficiency at 100% and above. In particular, InP-based integrated photonics allows implementation of SPECTS O-CDMA transmitters and receivers monolithically integrated on a chip. The integrated InP chip technology not only allows robust and compact configurations for practical and low-cost O-CDMA network deployments but also offers code reconfigurations at rapid rates for secure communication applications., QC 20100525

We present results of an experimental study of the timing and phase dynamics in a mode-locked Ti:sapphire laser. By measuring the response of two widely spaced comb lines to a sinusoidal modulation of the pump power, we determine quantitatively the response of both the central pulse time and the phase. Because of the distinct response of the pulse energy, central frequency, and gain to the modulation, we are able to distinguish their contributions to the timing and phase dynamics., Prepared in cooperation with the Department of Electrical and Computer Engineering, University of Colorado, Boulder, CO and Computer Science and Electrical Engineering Department, University of Maryland, Baltimore, MD. Published in Optic Letters, v32, n23, p3426-3428, 1 Dec 2007.

We investigate efficient frequency-doubling of low energy femtosecond pulses in bulk and waveguide nonlinear crystals, thereby demonstrating how to achieve a compact and portable ultrafast blue light Source. Using a femtosecond Cr:LiSAF laser (fundamental wavelength 860 nm) we examine the relative merits of the process of second harmonic generation (SHG) using bulk potassium niobate, bulk aperiodically-poled KTP, periodically-poled and aperiodically-poled KTP waveguide crystals. While SHG conversion efficiencies LIP to 37% were achieved using the waveguides, non-traditional strong focusing in the bulk samples yielded efficiencies of 30%. We have developed several theoretical models to accurately describe the temporal and spectral properties of the generated blue light, as well as the observed saturation behavior of the conversion process in the waveguide structures., Part of proceedings ISBN 1-4020-4164-0QCR 20190211

Efficient doubling of femtosecond pulses from a mode-locked Yb:KYW laser in periodically poled and aperiodically poled KTP is reported. Second-harmonic conversion efficiencies of up to 58% have been achieved and 354-fs pulses generated at 522nm., QC 20141111

Indium nitride (InN) is identified as a promising terahertz (THz) emitter based on the optical and electronic properties of high quality In- and N-face samples. Time domain THz spectroscopy has been employed to measure the pump wavelength and background carrier concentration dependence of THz emission from InN. There is no discernable difference between the In- and Nface InN samples, as expected for the improved crystalline quality and concomitant low background electron density and high mobility for both polarities. While there is only a weak dependence of THz signal on pump wavelength from 800 nm to 1500 nm, there is a strong dependence on background electron density. Modeling shows that the dominant mechanism for THz generation in bulk InN is the current associated with the diffusion of the photo-generated electrons at elevated electron temperature (photo-Dember effect) and the redistribution of the background electrons under drift, with larger screening from the higher mobility electrons as compared to holes. Compensation or p-type doping in conjunction with manipulation of the large internal electric fields in InN/InGaN nanostructures should lead to significant improvements in THz emitters., Prepared in collaboration with the Materials Department, University of California Santa Barbara, CA and Cornell University, Ithaca, NY. Presented at the Army Science Conference (25th), "Transformational Army Science and Technology - Charting the future of S&T for the Soldier," held in Orlando, Florida on 27-30 Nov 2006. Published in proceedings of the same. See also ADM002075, The original document contains color images.

We have been very productive during the entire funding period. We have reached all three goals listed in the project title well beyond the initial expectations and have published a number of high profile papers documenting these successes. We have given numerous invited talks on the research supported by AFOSR. We have achieved direct stabilization of a femtosecond-laser-based optical frequency comb by a high-finesse passive optical cavity. We carried out detailed comparison of two distinct stabilization schemes and the result leads to new understanding of the optimum conditions for cavity stabilization as well as on approaches to overcome limitations on the ability to transfer the frequency stability of the cavity to the microwave domain. The stability of the frequency comb is explored in both the optical and the radio frequency domain. With an independent, stable CW laser, we have verified that the line width and stability of the wide-bandwidth optical comb components, respectively, reach below 300 Hz and 5 x 10-14 at 1 s averaging time, both limited by the reference CW laser.

A practical efficient optical parametric chirped pulse amplification is demonstrated with periodically poled KTiOPO4. It provides a compact solution to amplify stretched pulses to the 100 muJ level (signal + idler) at 1 kHz. The amplified signal pulses near 1.57 mum are recompressed to 270 fs., QC 20100525

Our overall objective is to demonstrate powerful new signal processing functionalities for ultrafast optical signals, with an emphasis on proof-of-concept experiments of new space-time optical processing methods for digital logic operations, especially encryption and temporal pattern matching, on ultrafast optical bit streams. During this project period we focused on an optical space-to-time converter, which is one of the key subsystems in the envisioned space-time optical processing system. For the first time we have worked out how the dispersion varies with the positions of the constituent optical components, and we have verified our analysis experimentally. Our results demonstrate a means for compensating or controlling the chirp of the optical pulse sequences generated from the space-to-time converter, which is important for subsequent transmission in optical networks. Furthermore, our work show the possibility of using these space-to-time converters for generation of identical pulse sequences at a series of different wavelengths, with potential application to optical networks and photonic processing. Finally, for the first time we demonstrated generation of terahertz rate trains of optical pulses using an integrated component, which increases the opportunity for practical applications.

A new tvpe of accessible sources of ultrashort optical pulses based on the phenomenon of collective coherent recombination (superradiance) of electrons and holes in semiconductor heterostructures is proposed. The novel regime of an ultrafast operation of quantum well semiconductor lasers is analyzed, in which a quasiperiodic sequence of superradiant pulses of duration up to 30 fs and peak intenSity exceeding 100 MW/cm2 is emitted under a continuous pumping from a low-Q cavity of length of about 30-100 micrometers., Pres: 6th Int Symp Nanostructures: Physics and Technology, St Petersburg, Russia. 22-26 Jun 1998. p398-401. This article is from ADA406591 Nanostructures: Physics and Technology International Symposium (6th) held in St. Petersburg, Russia on June 22-26, 1998 Proceedings

We demonstrate optical parametric generation and amplification of femtosecond pulses in the entire visible range using type-I phase-matched beta-barium borate and lithium triborate crystals pumped by the frequency-doubled output of a Ti:sapphire regenerative amplifier at 395 nm. The output is tunable from 470 to 770 nm with a pulse width of similar to 170 fs at a repetition rate of 1 kHz and a a maximum output energy of similar to 1.1 mu J/pulse. The visible optical parametric amplifier output was then frequency doubled and sum frequency mixed with the fundamental output of Ti:sapphire at 790 nm to produce UV pulses with a conversion efficiency of greater than 25\%. The second harmonic generated UV pulses are tunable from 240 to 380 nm with a maximum pulse energy of similar to 260 nJ/pulse. (C) 1997 Optical Society of America.

We demonstrate optical parametric generation and amplification of femtosecond pulses in the entire visible range using type-I phase-matched beta-barium borate and lithium triborate crystals pumped by the frequency-doubled output of a Ti:sapphire regenerative amplifier at 395 nm. The output is tunable from 470 to 770 nm with a pulse width of similar to 170 fs at a repetition rate of 1 kHz and a a maximum output energy of similar to 1.1 mu J/pulse. The visible optical parametric amplifier output was then frequency doubled and sum frequency mixed with the fundamental output of Ti:sapphire at 790 nm to produce UV pulses with a conversion efficiency of greater than 25\%. The second harmonic generated UV pulses are tunable from 240 to 380 nm with a maximum pulse energy of similar to 260 nJ/pulse. (C) 1997 Optical Society of America.

We demonstrate optical parametric generation and amplification of femtosecond pulses in the entire visible range using type-I phase-matched beta-barium borate and lithium triborate crystals pumped by the frequency-doubled output of a Ti:sapphire regenerative amplifier at 395 nm. The output is tunable from 470 to 770 nm with a pulse width of similar to 170 fs at a repetition rate of 1 kHz and a a maximum output energy of similar to 1.1 mu J/pulse. The visible optical parametric amplifier output was then frequency doubled and sum frequency mixed with the fundamental output of Ti:sapphire at 790 nm to produce UV pulses with a conversion efficiency of greater than 25\%. The second harmonic generated UV pulses are tunable from 240 to 380 nm with a maximum pulse energy of similar to 260 nJ/pulse. (C) 1997 Optical Society of America.

By monitoring coenzyme autofluorescence modifications, as an indicator of cell damage, the cellular response to femtosecond near-infrared (NIR) radiation (two-photon absorption) was compared with exposure to low-power UVA radiation (one-photon absorption). Excitation radiation from a tunable Ti-sapphire laser, focused through high-numerical-aperture microscope optics, provided diffraction-limited microbeams of an adjustable peak power. Laser scanning NIR microscopy was used to detect spatially the intracellular distribution of fluorescent coenzymes by fluorescence intensity imaging as well as fluorescence lifetime imaging (tau-mapping). Upon the onset of UV or NIR exposure, Chinese hamster ovary cells exhibited blue/green autofluorescence with a mean lifetime of 2.2 ns, which was attributed to NAD(P)H in mitochondria. Exposure to 365 nm radiation from a high-pressure mercury lamp (1 mW, 300 J cm-2) resulted in oxidative stress correlated with increased autofluorescence intensity, onset of nuclear fluorescence, and a fluorescence lifetime decrease. The cellular response to femtosecond NIR microbeams depended significantly on peak power. Peak powers above a threshold value of about 0.5 kW (average power: 6 mW). 0.55 kW (7 mW) and 0.8 kW (10 mW) at 730 nm, 760 nm and 800 nm, respectively, resulted in the onset of short-lived luminescence with higher intensity (100 x) than the intracellular NAD(P)H fluorescence. This luminescence, accompanied by destruction of cellular morphology, was localized and occurred in the mitochondrial region. In contrast, beams at a power of less than 0.5 kW allowed nondestructive fluorophore detection with high spatial and temporal resolution without modification of cellular redox state or cell morphology.

By monitoring coenzyme autofluorescence modifications, as an indicator of cell damage, the cellular response to femtosecond near-infrared (NIR) radiation (two-photon absorption) was compared with exposure to low-power UVA radiation (one-photon absorption). Excitation radiation from a tunable Ti-sapphire laser, focused through high-numerical-aperture microscope optics, provided diffraction-limited microbeams of an adjustable peak power. Laser scanning NIR microscopy was used to detect spatially the intracellular distribution of fluorescent coenzymes by fluorescence intensity imaging as well as fluorescence lifetime imaging (tau-mapping). Upon the onset of UV or NIR exposure, Chinese hamster ovary cells exhibited blue/green autofluorescence with a mean lifetime of 2.2 ns, which was attributed to NAD(P)H in mitochondria. Exposure to 365 nm radiation from a high-pressure mercury lamp (1 mW, 300 J cm-2) resulted in oxidative stress correlated with increased autofluorescence intensity, onset of nuclear fluorescence, and a fluorescence lifetime decrease. The cellular response to femtosecond NIR microbeams depended significantly on peak power. Peak powers above a threshold value of about 0.5 kW (average power: 6 mW). 0.55 kW (7 mW) and 0.8 kW (10 mW) at 730 nm, 760 nm and 800 nm, respectively, resulted in the onset of short-lived luminescence with higher intensity (100 x) than the intracellular NAD(P)H fluorescence. This luminescence, accompanied by destruction of cellular morphology, was localized and occurred in the mitochondrial region. In contrast, beams at a power of less than 0.5 kW allowed nondestructive fluorophore detection with high spatial and temporal resolution without modification of cellular redox state or cell morphology.

We have achieved two objectives: (1) we developed the theory of electron scattering by adsorbed molecule and used it to demonstrate that electron scattering is a good probe of the orientation of a chemisorbed molecule. (2) We developed the theory of photodissociation with ultrashort pulses, analyzed existing experiments and showed that coherence and interference play a central role in the dissociation process. By using numerical simulations we proposed and documented new types of experiments which can increase the amount of information regarding dynamics of dissociation.

An anti-Stokes model is proposed which explains the room-temperature blue shift of the echo-signal spectrum compared to the spectrum of exciting femtosecond pulses in a polymer film doped with dye molecules. The possibility of realising the anti-Stokes regime of coherent laser cooling of such films is analysed. © 2007 Kvantovaya Elektronika and Turpion Ltd.

An anti-Stokes model is proposed which explains the room-temperature blue shift of the echo-signal spectrum compared to the spectrum of exciting femtosecond pulses in a polymer film doped with dye molecules. The possibility of realising the anti-Stokes regime of coherent laser cooling of such films is analysed. © 2007 Kvantovaya Elektronika and Turpion Ltd.