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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. This supports the notion that the observed difference in SHG and MAIL in the studied nanocomposite systems is due to the shape modification mechanism. The discrete dipole approximation method was used to assess the absorption and scattering cross-sections of the reshaped NPs with different elongation ratios.

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. The presented approach may lead to sophisticated marking of information in metal-glass nanocomposites.

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. We have also revealed the existence of two orthogonally polarized 'free' rays for particular orientations of the incident beam polarization.

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. The associated spatial walk-off can also preclude the phase retardation approximation used in THz-TDS. The rate of misalignment-induced chirping in commonly used ZnTe and GaP schemes is tabulated, allowing ready analysis of a detection system.

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. Comparison with theory shows agreement with the experimentally observed results.

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. The process was then studied as a function of the laser polarization, repetition rate and the number of pulses fired per spot.

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 0.4 kV and 0.6 kV at an elevated temperature of 200 °C for 30 minutes across the nanocomposites led to the formation of a periodic array of embedded structures of metallic nanoparticles. The current-time dynamics of the structuring processes, optical analyses of the structured nanocomposites and diffraction pattern of one such fabricated element are presented.

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.

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 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.

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.

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. Since the length of the chirped laser pulse can be easily changed, the electron bunch can be visualized on different time scales. This single-shot imaging technique is a promising method for real-time electron-bunch diagnostics.

Holographic recording with orthogonally polarized beams in a cesium-doped KNSBN [(K0.5Na0.5)0.2(Sr0.75Ba0.25)0.9Nb2O6] crystal has been studied. It was found that this kind of photorefractive crystal possesses high linear dichroism, which makes it suitable for use in polarization holography. The diffraction efficiency as a function of the polarization orientation of the reference beam and as a function of the fringe modulation at the optimum polarization orientation of the reference beam is experimentally investigated. Theoretical fitting based on Kahmann models was performed and agrees well with the experimental data. In the experiments, both polarization holography and conventional holography are used to record a binary object. The reconstruction shows that polarization holography with Ce:KNSBN is highly effective, exhibiting high diffraction efficiency and reduced fanning noise.

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 1.9-times enhancement of the gain and nearly 3-times enhancement of the signal-to-noise ratio were achieved at a signal-to-pump beam intensity ratio of 1:40. At a beam intensity ratio of 1:2000, a two-wave coupling gain of nearly 500 was obtained, which is much higher than the gain previously reported. Modified coupled-wave equations that involve beam fanning with certain assumptions concerning the fanning parameters were used. The numerical solution is in good agreement with the experimental data. The results are compared with those obtained with a 45 degrees -cut BaTiO(3) crystal.

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. Especially in the latter case, reconstruction of the longitudinal electron bunch shape is straightforward.

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. The optical pulses have a full width at half maximum time-bandwidth product Deltat(FWHM)Deltaf(FWHM) of 0.2-0.3. The results presented here can be used to predict the optical pulse length and corresponding minimum spectral width that can be generated in a FEL pumped by short electron bunches. This is important for the design of new infrared free-electron laser user facilities, which need to make a balanced choice between short pulses for high temporal resolution and narrow bandwidth for linear and nonlinear spectroscopy.

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 3.7, whereas the diffraction at low fringe modulations is suppressed by a factor of 0.6. The proposed technique has the advantages of real-time enhancement, arbitrary selection of the spatial frequency to be enhanced, and improved stability of the output. Experimental results of the edge enhancement of objects and edge-enhanced correlation are presented.

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.

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. There are two main advantages in using moving gratings: First, the signal-to-noise ratio can be improved considerably because of the improved diffraction efficiency. Second, the resonant effect reduces the effect of environmental disturbances on the peak-correlation intensity, which is significant when the threshold detection level of the correlator is set.

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

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.

Postoperative chest infection was studied prospectively in 73 patients in order to evaluate standard laboratory methods of sputum examination and to relate the results to the patients' clinical state and to antibiotic therapy. When a culture medium selective for haemophilus was used in addition to unselective media, homogenisation of the specimen gave no advantage. Laboratory and clinical findings usually corresponded well. Profuse growths of Streptococcus pneumoniae or Haemophilus influenzae were clearly associated with clinical evidence of chest infection but other Gramnegative bacilli and Staphylococcus aureus much less so. Coliforms were more prominent after antibiotic therapy.

The value of postoperative bladder irrigation with the antiseptic agent chlorhexidine was assessed in a randomized prospective controlled study of men after transurethral operations. In patients with sterile preoperative urine the incidence of postoperative bacteriuria was 12.8 per cent, compared to 36.7 per cent in control patients. The difference is significant (chi-square 5.54, p less than 0.02). On the other hand, chlorhexidine irrigation did not eliminate pre-existing infection. Small amounts of chlorhexidine were demonstrated in the blood of some patients. There was no evidence of damage to the bladder and no toxic side effects.

The relation between the timing of prophylactic antibiotic administration and the occurrence of bacteraemia during transurethral operations was studied in 112 patients whose urine was infected before operation. Blood cultures taken during operation were positive in 15 (60%) of 25 patients who did not receive appropriate antibiotics, in 13 (21%) of 63 patients who were given appropriate antibiotics less than 24 h before operation, and in none of 24 patients in whom antibiotic "cover" was started more than 24 h before operation. In all cases the bacteraemia was transient. No patient developed septicaemia. The implications of these findings for the optimum timing of antibiotic administration to patients with preoperative bacteriuria are discussed.

Acute urinary tract infections in young women attending a clinic for sexually transmitted diseases were caused by the same bacteria, in the same proportions, as those that caused infections in women students. Staphylococcus saprophyticus biotype 3 (formerly called Micrococcus subgroup 3) was the commonest organism after coliform bacilli and caused about 30% of the infections. It was uncommon in women over 25 years of age and rarely caused asymptomatic bacteriuria in pregnancy. Most infections, irrespective of the causative organism, started soon after sexual intercourse, but neither the staphylococci nor the other organisms were associated with promiscuity, as judged by numbers of sexual partners or the incidence of sexually transmitted diseases. There was no evidence that the staphylococci were sexually transmitted. The reasons for the virulence of Staph. saprophyticus and its predilection for the urinary tract of young women remain unknown.

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. The numbers of leucocytes in urine were also similar in both patients and controls. Our findings support the view that the urethral syndrome is not caused by bacterial or chlamydial infection.

The protective effect of treating the skin of newborn infants with powders containing 1% chlorhexidine or 0.33% hexachlorophane was compared. Each was equally effective in preventing colonisation and infection by Staphylococcus aureus. In contrast, the skin became profusely colonised by coagulase-negative staphylococci, irrespective of the powder used. Venous blood concentrations of chlorhexidine were low or undetectable in the few infants whose blood was analysed.

Chemoprophylaxis and disinfection of the operation site for the prevention of bacteriuria after a transurethral operation were assessed in controlled, prospective studies in men with sterile urine preoperatively. The majority of the control patients (65 per cent) suffered postoperative bacteriuria compared to 38.6 per cent after perioperative disinfection with chlorhexidine and 10 per cent or less after each of 2 other regimens (intramuscular cephradine followed by oral nitrofurantoin and chlorhexidine disinfection followed by oral nitrofurantoin). The latter regimen is preferred since it avoids the use of agents with systemic action.

A novobiocin-resistant "biotype" of Micrococcus subgroup 3 (Staphylococcus saprophyticus) is known to be a primary pathogen of the female urinary tract and to cause infections as severe as those produced by Escherichia coli. The growth characteristics of this virulent biotype were compared in vitro with those of other Micrococcaceae and of E. coli to determine whether rapid growth explains the virulence of the biotype. Nutrient broth was shown to have growth-supporting qualities that differed from those of urine and it was therefore unsuitable for these studies. In urine, the virulent biotype grew more slowly, had a longer lag period, and reached much lower final viable counts than did Escherichia coli. Surprisingly, the virulent biotype also grew more slowly and reached a lower final viable count than did several other Micrococcaceae isolated from the urinary tract of healthy women. Urine from women who had suffered a recent infection with the virulent biotype had growth-supporting properties similar to those of urine from healthy women. Experiments with filtered forestream urine suggested that urethral secretions do not contain a factor determining growth rates of this organism in urine. The possibility that virulent strains adapt to rapid growth in urine was excluded. No evidence was obtained that the virulent biotype inhibits the growth of other Micrococcaceae in urine. Ability to grow rapidly in urine does not therefore explain the virulence of novobiocin-resistant strains of subgroup-3 micrococci.

Men with indwelling catheters and men and women with suprapubic catheters were studied in their homes. Urine and blood were cultured and body temperature recorded after every catheter change. Nearly all patients had infected urine after 4 weeks of catheterisation, and all had bacteriuria after longer periods, usually with a mixture of organisms. Culture on selective media revealed a wider range of organisms than was detected on routine C.L.E.D. and blood agar with antibiotic sensitivity disks, but routine culture gave adequate information for clinical purposes. Bacteraemia was demonstrated after 20 of 197 changes of urethral catheter and after one of 19 changes of suprapubic catheter; but no patient had pyrexia or other symptoms. However, two had rigors on other occasions. When assessing "risk factors" for blood-stream infection in catheterised patients, it is important to record the total incidence of bacteraemia, asymptomatic as well as symptomatic.

In a maternity hospital in which the umbilicus and trunk of healthy newborn infants were treated with 0.33% hexachlorophane dusting powder, the hexachlorophane content of blood was measured in mothers before delivery, in infants' umbilical samples at birth, and at 8 days of age in capillary blood samples. One mother and her baby had rather high blood concentrations of hexachlorophane, probably derived from a toilet preparation used before admission to hospital. Hexachlorophane was absent or barely detectable in the other mothers' blood and in the infants' umbilical blood. The hexachlorophane concentrations in the blood of 8-day-old infants ranged from nil to 0.166 mug./ml. (mean 0.066 mug./ml.). These were much less than the concentrations reported to be toxic in animals.In a previous trial now reported here, a dusting powder containing chlorhexidine instead of hexachlorophane was found to delay the separation of the umbilical cord.

In a prospective study in young women, novobiocin-resistant subgroup-3 micrococci were the second commonest cause, after Escherichia coli; of acute urinary infections. Proteus mirabilis was the only other causative organism. Symptoms, pyuria, or possible aetiological factors were the same in micrococcal and coliform infections. The infecting micrococcus "biotype" was only rarely found among the normal flora of the genitourinary tract of young women, though other micrococci and staphylococci were commonly present. Evidently, the infecting micrococci are selectively pathogenic in the urinary tract. Micrococcal infections, like coliform infections; commonly followed sexual intercourse, but there was no evidence that the micrococci were sexually transmitted. The infecting biotype was rarely found in the male urethra or prepuce.

Septicemia occurred in 18 of 1,604 patients subjected to transurethral resection (TUR) of the prostate. Six patients died postoperatively, 4 of septicemia. In 11 patients septicemia was provoked by TUR in the presence of urinary infection and in the absence of appropriate antibiotic cover. Septicemia was provoked by catheter removal in 2 similarly infected patients. In the remaining 5 patients the urine was sterile at operation but became infected prior to catheter removal, and this maneuver precipitated septicemia.

The value of adding chlorhexidine to urine drainage bags of male patients treated with indwelling catheters after prostatectomy and other transurethral operations was assessed in a randomised, prospective, controlled was assessed in a randomised, prospective, controlled study. Chlorhexidine kept the contents of all drainage bags sterile, but the frequency of urinary infection in the chlordexidine group (51%) did not differ significantly from that in the control group (45%). Most infections were endogenous, caused by organisms which probably came from the patient's own urethra. It was concluded that the method has no value in urology units where standards of catheter care and closed drainage are properly maintained. Controlled studies in other types of catheterised patients are needed, especially when the risks of cross-infection are high.