On second harmonic generation and multiphoton-absorption induced luminescence from laser-reshaped silver nanoparticles embedded in glass.

Spherical silver nanoparticles (NPs) of 30 nm diameter embedded in soda-lime glass were uniformly reshaped (elongated) after irradiation by a linearly polarised 250 fs pulsed laser operating within the NPs' surface plasmon resonance band. We observed second harmonic generation (SHG) and multiphoton-absorption-induced luminescence (MAIL) in the embedded laser-reshaped NPs upon picosecond (10 ps) pulsed laser excitation at 1064 nm. A complementary study of SHG and MAIL was conducted in soda-lime glass containing embedded, mechanically-reshaped silver NPs of a similar elongation ratio (aspect ratio) to the laser-reshaped NPs.

Radially and azimuthally polarized laser induced shape transformation of embedded metallic nanoparticles in glass.

Radially and azimuthally polarized picosecond (~10 ps) pulsed laser irradiation at 532 nm wavelength led to the permanent reshaping of spherical silver nanoparticles (~30 - 40 nm in diameter) embedded in a thin layer of soda-lime glass. The observed peculiar shape modifications consist of a number of different orientations of nano-ellipsoids in the cross-section of each written line by laser. A Second Harmonic Generation cross-sectional scan method from silver nanoparticles in transmission geometry was adopted for characterization of the samples after laser modification.

On the frequency-doubled conically-refracted Gaussian beam.

A Potassium Titanyl Phosphate (KTP) crystal has been used in conjunction with a 10-ps pulsed laser to produce a frequency-doubled conically-refracted Gaussian beam. The 'free' and 'forced' beams that make up the scheme for nonlinear conical refraction were readily observable in non-phase-matched conditions. The dependency of the frequency-doubled beam patterns on the incident beam polarization, which until now has remained unexplored, was examined in detail.

Role of misalignment-induced angular chirp in the electro-optic detection of THz waves.

A general description of electro-optic detection including non-collinear phase matching and finite transverse beam profiles is presented. It is shown theoretically and experimentally that non-collinear phase matching in ZnTe (and similar materials) produces an angular chirp in the χ(2)-generated optical signal. Due to this, in non-collinear THz and probe arrangements such as single-shot THz measurements or through accidental misalignment, measurement of an undistorted THz signal is critically dependent on having sufficient angular acceptance in the optical probe path.

Azimuthally and radially polarized light in conical diffraction.

Azimuthal and radial polarization states of light are used to produce conical diffraction (CD) from a KGd(WO4)2 crystal. The patterns produced in the ring plane in each case display marked differences than those seen when linearly polarized incident light is used, with the production of a splitting of the CD ring into two concentric rings of equal intensity. The free space evolution for each type of polarization state is also experimentally recorded and investigated.

Picosecond pulsed laser induced optical dichroism in glass with embedded metallic nanoparticles.

Picosecond (~10 ps) pulsed laser irradiation at 532 nm led to the efficient and scalable fabrication of dichroic areas in glass with spherical silver nanoparticles of ~30 - 40 nm in diameter embedded in a surface layer of thickness ~20 μm. The observed dichroism is due to the uniform and permanent shape transformation of the nanoparticles - from spherical to spheroidal shapes - throughout the irradiated areas and along the laser polarization direction, paving the way for affordable manufacture of polarization-selective diffractive optical elements. The shape modification threshold and the dichroism as a result of Surface Plasmon Resonance band separation were identified.

Diffractive optical element embedded in silver-doped nanocomposite glass.

A diffractive optical element is fabricated with relative ease in a glass containing spherical silver nanoparticles 30 to 40 nm in diameter and embedded in a surface layer of thickness ~10 μm. The nanocomposite was sandwiched between a mesh metallic electrode with a lattice constant 2 μm, facing the nanoparticle containing layer and acting as an anode, and a flat metal electrode as cathode. Applying moderate direct current electric potentials of 0.

Holographic recording with orthogonally polarized beams in a cesium-doped (K0.5Na0.5)0.2(Sr0.75Ba0.25)0.9Nb2O6 crystal.

Holographic recording with orthogonally polarized beams in a cesium-doped KNSBN [(K0.5Na0.5)0.

Enhancement of Two-Wave Coupling in a Ce:KNSBN Crystal with Optimum Polarization of the Writing Beams.

We have improved the two-wave coupling amplification and the signal-to-noise ratio of an amplified signal with photorefractive cerium-doped potassium sodium strontium barium niobate (Ce:KNSBN) by employing optimum polarization orientation of the pump beam while the signal beam retains extraordinary polarization. The optimum polarization angle of the pump beam was found experimentally to be 30 degrees with respect to the extraordinary polarization direction in a symmetrically incident system. Nearly 1.

Edge enhancement by use of moving gratings in a bismuth silicon oxide crystal and its application to optical correlation.

The technique of moving gratings in a photorefractive crystal is applied to the edge enhancement of objects and edge-enhanced optical correlation. The nonlinear dependence of the optimum fringe velocity on the fringe modulation and the variation of the enhancement of the diffraction efficiency with fringe modulation at a fixed fringe velocity appropriate to high fringe modulations are experimentally investigated. It is shown that the diffraction at high fringe modulations, which corresponds to the high-spatial-frequency components of the Fourier spectrum, is enhanced by a factor of approximately 3.

Benchmarking of electro-optic monitors for femtosecond electron bunches.

The longitudinal profiles of ultrashort relativistic electron bunches at the soft x-ray free-electron laser FLASH have been investigated using two single-shot detection schemes: an electro-optic (EO) detector measuring the Coulomb field of the bunch and a radio-frequency structure transforming the charge distribution into a transverse streak. A comparison permits an absolute calibration of the EO technique. EO signals as short as 60 fs (rms) have been observed, which is a new record in the EO detection of single electron bunches and close to the limit given by the EO material properties.

Temporally resolved electro-optic effect.

The electro-optic effect between an ultrafast optical probe pulse and an ultrashort terahertz pulse is shown to depend on the time derivatives of the product of the probe and terahertz electric fields. Application of this theory to temporally resolved single-shot terahertz detection techniques, where the electro-optic effect is temporally localized within an optical probe pulse, shows that the description presented here differs fundamentally and verifiably from that commonly used in literature.

Electro-optic technique with improved time resolution for real-time, nondestructive, single-shot measurements of femtosecond electron bunch profiles.

Electro-optic detection of the Coulomb field of a relativistic electron bunch combined with single-shot cross correlation of optical pulses is used to enable single-shot measurements of the shape and length of femtosecond electron bunches. This method overcomes a fundamental time-resolution limit of previous single-shot electro-optic measurements, which arises from the inseparability of time and frequency properties of the probing optical pulse. Using this new technique we have made real-time measurements of a 50 MeV electron bunch, observing the profile of 650 fs FWHM ( approximately 275 fs rms) long bunches.

High-temporal-resolution, single-shot characterization of terahertz pulses.

A technique for noncollinear cross correlation of electro-optic modulated optical pulses is presented for the single-shot characterization of terahertz waveforms and is compared to established electro-optic terahertz characterization methods. This technique is free from the limitations on time resolution and faithful reproduction of previously demonstrated single-shot amplitude modulation spectral encoding.

Single-shot electron-beam bunch length measurements.

We report subpicosecond electro-optic measurements of the length of individual relativistic electron bunches. The longitudinal electron-bunch shape is encoded electro-optically on to the spectrum of a chirped laser pulse. The electron-bunch length is determined by analyzing individual laser-pulse spectra obtained with and without the presence of an electron bunch.

Formation of low time-bandwidth product, single-sided exponential optical pulses in free-electron laser oscillators.

The detailed shape of picosecond optical pulses from a free-electron laser (FEL) oscillator has been studied for various cavity detunings. For large values of the cavity detuning the optical pulse develops an exponential leading edge, with a time constant proportional to the applied cavity detuning and the quality factor of the resonator. This behavior has been observed at two separate FELs that have completely different resonator layouts and electron beam characteristics, and using different methods of optical pulse length measurement.

Subpicosecond electro-optic measurement of relativistic electron pulses.

Time-resolved measurements of the transverse electric field associated with relativistic electron bunches are presented. Using an ultrafast electro-optic sensor close to the electron beam, the longitudinal profile of the electric field was measured with subpicosecond time resolution and without time-reversal ambiguity. Results are shown for two cases: inside the vacuum beam line in the presence of wake fields, and in air behind a beryllium window, effectively probing the near-field transition radiation.

Effects of optical bias on moving gratings in bismuth silicon oxide at large fringe modulation.

Optical bias has been applied in the formation of moving gratings in bismuth silicon oxide at large fringe modulations. It is shown that optical bias is an effective method of overcoming the problems associated with the sudden drop in the optimum fringe velocity when the fringe modulation is close to unity. It is experimentally found that within a certain range of optical bias the absolute diffraction efficiency can be higher than that without optical bias, which is not the case when a stationary grating is used.

Holographic-recording improvement in a bismuth silicon oxide crystal by the moving-grating technique.

We investigate the enhancement of the diffraction efficiency of dynamic gratings recorded in a bismuth silicon oxide crystal at large modulation by the moving-grating technique. The optimum fringe velocity for maximum diffraction efficiency and the degree of enhancement of the diffraction efficiency at optimum fringe velocity are experimentally found to be dependent on the fringe modulation. We apply this technique to real-time incoherent correlation using bismuth silicon oxide.

Real-time color image correlation with a color liquid-crystal television and a Fresnel holographic filter.

Incoherent color image correlation with a multiwavelength Fresnel holographic filter and a color liquid-crystal television as a real-time input device is demonstrated.

Optical pattern recognition using a synthetic discriminant amplitude-compensated matched filter.

A technique for optical pattern recognition using an amplitude-compensated matched filter is presented. With the synthetic discriminant function in a matched spatial filtering application an iterative technique is employed to first obtain the synthetic discriminant functions for the phase-only matched filter and then is extended to the amplitude-compensated matched filter. Computer simulation shows that the suggested spatial filter has a high signal-to-noise ratio and good Horner efficiency, and it is more sensitive to changes in the input image.

Microbiology of the urethral (frequency and dysuria) syndrome. A controlled study with 5-year review.

In a clinical and microbiological study of women with urinary frequency and dysuria (excluding those with bacterial cystitis), 41 patients were compared with 42 control subjects. No difference was found between patients and controls in the incidence of infection by Chlamydia trachomatis or other sexually transmitted organisms. The numbers of lactobacilli and other fastidious organisms in the urine of patients with either mild or severe symptoms were similar and did not differ from the numbers in the urine of control subjects.