Matrix-free laser desorption/ionization-mass spectrometry using self-assembled germanium nanodots

A novel ionization platform for matrix-free laser desorption/ionization-mass spectrometry (LDI-MS) was developed using self-assembled germanium nanodots (GeNDs) of uniform size (approximately 150 - 200-nm width and approximately 50-nm height) grown on a silicon wafer produced by molecular beam epitaxy. The performance of LDI-MS using GeNDs (GeND-MS) was investigated through measurements of a broad range of analytes, including peptides, proteins, synthetic oligomers, and polymer additives. Mass spectra of tryptic digests were clearly observed even for the mass range lower than m/z 800 without obstructive peaks. A detection limit of subfemtomole level was achieved for angiotensin-I. The upper limit of detectable mass range was approximately 17 kDa (myoglobin). GeND-MS also has potential for application to the characterization of industrial compounds. Almost accurate molecular weight distribution was obtained for a nonionic surfactant (Triton X-100) and for poly(ethylene glycol) oligomer. Furthermore, a brominated flame retardant, tetrabromobisphenol-A bis(2,3-dibromopropyl ether), was successfully ionized with less fragmentation, a result not obtainable by matrix-assisted laser desorption/ionization-mass spectrometry or desorption/ionization on porous silicon-mass spectrometry.     

Broadband flexible waveguides for free-electron laser radiation

We refined flexible waveguides previously developed for CO(2) and Er:YAG laser radiation to transmit free-electron-laser (FEL) radiation. One can tune this laser over several segments of the radiation spectrum. This laser has a high peak power of as much as 10 MW with pulse energy of as much as 100 mJ. We made the waveguides of either Teflon or fused-silica tubes internally coated with metal and dielectric layers. We optimized the internal coatings specifications for transmission of various radiation wavelengths in the mid-IR range and enabled transmission of high-peak radiation. We performed experiments in three major FEL sites in the United States over a more than 1-year period when we measured and examined various characteristics of transmission. We used the analysis of these experiments as feedback to further improve these waveguides. The good preliminary results encourage us to invest more effort to further develop these waveguides until a suitable waveguide is obtained for this type of laser and make possible its introduction to the medical field where its characteristics can be exploited in surgical applications.     

Macroparticle theory of a standing wave free-electron laser two-beam accelerator

Free-electron laser operation is formulated using a macroparticle approach based on a universal gain equation. Microwave excitation in a single cavity is derived analytically and is given in the form of analytic recursion equations for a multicavity system driven by a sequence of electron bunches. Qualitative and quantitative insights into the basic excitation and saturation mechanisms are provided. Stability analysis on a test particle moving around a macroparticle shows the importance of precise control of bunch spacing.     

Hollow-glass waveguide delivery of an infrared free-electron laser for microsurgical applications

The purpose of this research is to deliver free-electron-laser (FEL) pulses for intraocular microsurgery. The FEL at Vanderbilt University is tunable from 1.8 to 10.8 mum. To deliver the FEL beam we used a metallic-coated hollow-glass waveguide of 530-mum inner diameter. A 20-gauge cannula with a miniature CaF(2) window shielded the waveguide from water. Open-sky retinotomy was performed on cadaver eyes. The system delivered as much as 6 x 10(5) W of FEL peak power to the intraocular tissues without damage to the waveguide or to the surgical probe.     

Generation of induced Smith-Purcell radiation: free-electron laser in open system

We have used the framework of the dispersion equation to study coherent Smith–Purcell (SP) radiation induced by a relativistic magnetized electron beam in the absence of a resonator. As an important example of the application of the obtained results of our previous paper JMO v.57, 2060, (2010) the growth rate of SP FEL in the case with a rectangular grating was calculated. The growth rate of the instability is proportional to the square root of the electron beam current. The calculated results are consistent with the experimental data obtained by Urata et al. [Phys. Rev. Lett. 80, 516 (1998)].     

Salient features of using a free-electron laser with a crossed fluted cavity for generating coherent tunable gamma radiation

A new way of generating high-power tunable coherent gamma radiation in a free electron laser with a crossed fluted cavity is proposed. The gamma rays are generated in the inverse Compton scattering of intracavity radiation on the electron beam of the free-electron laser. The use of a crossed fluted cavity makes it possible to raise substantially the intracavity power and thereby the power of the gamma radiation and also to solve the problem of extraction of the hard radiation while eliminating the hitherto unavoidable losses in passage through the material of the cavity mirror. Pis’ma Zh. Tekh. Fiz. 25, 89–94 (May 26, 1999)     

On the theory of a plasma-beam superheterodyne free-electron laser with H-ubitron pumping

The scheme of a plasma-beam superheterodyne free-electron laser (PBSFEL) with H-ubitron pumping is analyzed and several possible variants of its practical implementation are considered. Some variants represent sources of highly monochromatic signals, while the other generate signals with a rather broad spectrum. The increment of wave growth in PBSFELs is estimated and it is established that, under otherwise equal conditions, these FELs are characterized by much greater gain increments than the equivalent two-stream devices. The proposed PBSFELs have good prospects as sources of high-power electromagnetic radiation in the millimeter wavelength range.     

Camera for coherent diffractive imaging and holography with a soft-x-ray free-electron laser

We describe a camera to record coherent scattering patterns with a soft-x-ray free-electron laser (FEL). The camera consists of a laterally graded multilayer mirror, which reflects the diffraction pattern onto a CCD detector. The mirror acts as a bandpass filter for both the wavelength and the angle, which isolates the desired scattering pattern from nonsample scattering or incoherent emission from the sample. The mirror also solves the particular problem of the extreme intensity of the FEL pulses, which are focused to greater than 10(14) W/cm2. The strong undiffracted pulse passes through a hole in the mirror and propagates onto a beam dump at a distance behind the instrument rather than interacting with a beam stop placed near the CCD. The camera concept is extendable for the full range of the fundamental wavelength of the free electron laser in Hamburg (FLASH) FEL (i.e., between 6 and 60 nm) and into the water window. We have fabricated and tested various multilayer mirrors for wavelengths of 32, 16, 13.5, and 4.5 nm. At the shorter wavelengths mirror roughness must be minimized to reduce scattering from the mirror. We have recorded over 30,000 diffraction patterns at the FLASH FEL with no observable mirror damage or degradation of performance.     

Solution-phase synthesis of germanium nanoclusters using sulfur

Sulfur is used to promote the formation of germanium nanocrystals from the robust organometallic precursor, triphenylgermanium chloride, at elevated temperatures (300?°C) in the surfactant/solvent hexadecylamine. Transmission electron microscopy shows that 8?nm germanium nanocrystals are produced that self-assemble into uniform-sized 60?nm germanium nanoclusters after purification. Electron diffraction studies show that the germanium nanoclusters have a diamond germanium crystal structure and energy dispersive x-ray spectroscopy shows that the nanoclusters are primarily composed of pure germanium.     

A traveling-wave ring resonator with Bragg deflectors in a two-stage terahertz free-electron laser

We propose a scheme of a two-stage terahertz free-electron laser (FEL) based on a Bragg traveling-wave ring resonator and parallel ribbon relativistic electron beams. The first beam moves in the field of a planar undulator and generates a pumping wave in the millimeter range. At the second stage, this wave transforms into terahertz radiation in the course of intraresonator backscattering on the second parallel electron beam. The ring resonator consists of four Bragg deflectors, each deflecting radiation by 90° in the vicinity of Bragg resonance, thus closing the feedback ring of the low-frequency pumping generator and simultaneously providing effective transfer of the pumping wave to the scattering stage.     

Temperature alterations of infrared light absorption by cartilage and cornea under free-electron laser radiation

Like pure water, the water incorporated into cartilage and cornea tissue shows a pronounced dependence of the absorption coefficient on temperature. Alteration of the temperature by radiation with an IR free-electron laser was studied by use of a pulsed photothermal radiometric technique. A computation algorithm was modified to take into account the real IR absorption spectra of the tissue and the spectral sensitivity of the IR detector used. The absorption coefficients for several wavelengths within the 2.9- and 6.1-microm water absorption bands have been determined for various laser pulse energies. It is shown that the absorption coefficient for cartilage decreases at temperatures higher than 50 degrees C owing to thermal alterations of water-water and water-biopolymer interactions.     

Non-invasive study of nerve fibres using laser interference microscopy

This paper presents the results of a laser interference microscopy study of the morphology and dynamical properties of myelinated nerve fibres. We describe the principles of operation of the phase-modulated laser interference microscope and show how this novel technique allows us to obtain information non-invasively about the internal structure of different regions of a nerve fibre. We also analyse the temporal variations in the internal optical properties in order to detect the rhythmic activity in the nerve fibre at different time scales and to shed light on the underlying biological processes. We observe pronounced frequencies in the dynamics of the optical properties and suggest that the oscillatory modes have similar origin in different regions, but different strengths and mutual modulation properties.     

Effect of laser irradiation on the electrical properties of amorphous germanium films

Amorphous films of germanium were grown using a vacuum evaporation technique, on glass substrates kept at room temperature. As-grown films were irradiated with Q-Switched Nd-YAG laser pulses (=1.06 m, 20nsec, 10 to 50Jcm^–2). The d.c. conductivity measurements were made in the temperature range 77 to 300 K. It was observed that the effect of laser irradiation was similar to the effect caused by the thermal annealing of the films. The d.c. conductivity data were analysed in the light of Mott's theory of a variable range hopping conduction process.     

Propagation of Hermite-cosh-Gaussian laser beams in non-degenerate germanium having space charge neutrality

In this paper, we analytically investigate Hermite-cosh-Gaussian (HChG) laser beam propagation in non-degenerate germanium having space charge neutrality for the first three mode indices. The field distribution in the medium is expressed in terms of beam-width parameter f and decentred parameter b. The differential equations for the f parameter are established by a parabolic wave equation approach under paraxial approximation. Analytical solutions are obtained under the condition R _n < R _d , where R _n is the self-focusing length and R _d is the diffraction length. The behaviour of the f parameter with the dimensionless distance of propagation η for various b values is examined by numerical estimates. The results are presented graphically.     

Ellipsometric study of thermally evaporated germanium thin film

The optical properties of thermally evaporated germanium thin films in the spectral range 0.3-1.7 mum were studied with spectroscopic ellipsometry. The microstructure of these films, including their crystallinity, density, surface morphology, and surface oxidation, was analyzed with x-ray diffraction, Rutherford backscattering spectrometry, atomic force microscopy (AFM), and Auger electron spectrometry (AES). Parameters such as the surface roughness and surface-oxidation-layer thickness, derived from AFM and AES measurements, were incorporated into our optical model. The complex index of refraction (n and k) of the films was determined throughout the above spectral range and compared with that of single-crystal germanium.     

Pulsed cyclic heating of copper surface using high-power 30-GHz free-electron maser

Thermal fatigue of the surface of copper subjected to multiply repeated pulsed microwave heating has been studied in order to estimate the maximum permissible acceleration rate for the CLIC collider at CERN. For this purpose, the damage of copper rings in a test cavity of the JINR-IAP facility was traced under the action of 10⁴–10⁵ microwave pulses at a temperature rise up to 190–250 K in every pulse. The test cavity was loaded by pulses of a high-power 30-GHz free-electron maser. Data on the dynamics of damage developed on the copper surface under the action of a strong electromagnetic field in the cavity are presented.     

Transmission laser microscope using the phase-shifting technique and its application to measurement of optical waveguides

A type of a transmission phase-shifting laser microscope, believed to be new, has been developed. In this microscope a biprism located between a magnifying lens and an observation plane was used as a beam splitter. The biprism is laterally translated to introduce phase shifts required for quantitative phase measurement with a phase-shifting technique. The disturbance caused by a Fresnel-diffracted wave from the splitting edge of the biprism is reduced by placement of a linear beam stopper at the center of an intermediate image plane. As the first application, the developed microscope is used to measure a refractive-index distribution in optical waveguides. A difference of refractive indices of less than 6 x 10(-5) is clearly measured in the submicrometer region.     

Betatron contributions to the angular gain spectrum of a free-electron laser with an imperfect beam trajectory

The effect of betatron oscillations on the angular gain spectrum of a free-electron laser is examined in the case of an imperfect beam trajectory. The use of an axial magnetic field is suggested to improve the beam–mode coupling and gain of the laser.     

Diagnostic techniques and UV-induced degradation of the mirrors used in the Orsay storage ring free-electron laser

Due to its low gain, the Orsay storage ring free-electron laser necessitates the use of high reflectivity mirrors. Three techniques for measuring the mirror losses are presented, based on cavity decay time measurements using either an external laser, the synchrotron radiation stored in the cavity, or the free-electron laser itself. The high signal-to-noise ratio allowed the detection of loss variations as low as 10(-7)/sec(1/2). From these diagnostics three distinct processes of UV-induced degradation of TiO2/SiO2 dielectric mirrors were identified. One was a surface absorption of the upper SiO2-air interface; it was not affected by annealing. The other two corresponded to a volume absorption of the layers which completely recovered after annealing.