Frequency-doubled Nd-YAG Laser Research Articles

Discovery of new even-parity fine structure levels of Pr I with angular momenta 1/2, 3/2, and 5/2

The spectrum of Praseodymium was investigated in the visible region from 4000 Å to 7500 Å based on previously recorded Fourier Transform spectra. Source of free Pr atoms was a hollow cathode discharge lamp. The investigation of spectral lines was performed using laser-induced fluorescence spectroscopy. A tunable single mode ring-dye laser, pumped by a frequency doubled Nd-YAG laser, was used as the light source to investigate selected lines. Hyperfine spectra of 129 lines were recorded and the magnetic dipole hyperfine structure constants of the involved energy levels were determined. This led to the discovery of up to now unknown levels. In this paper, 30 even parity levels, having J-values of 1/2, 3/2, and 5/2 are presented. The existence of all levels is confirmed by several laser excitations in the spectral range of our dye laser.

Energy transfer studies for the liquid and solid state materials of Rhodamine B and Styryl 7 Dye

Samples of dye doped Rhodamine B and Styryl 7 with MMA in solid state and the dye mixture in liquid state were prepared. Frequencydoubled Nd-YAG laser was used to evaluate solid and liquid dye samples laser emission. Using dye cell and dye-coated prism setup, distributed feedback dye laser(DFDL) activity was initiated. The dependence of pulse widths, and output power on acceptor – donor concentrations and pump power were analyzed in theoretical form. The resulting output energy of DFDL for liquid and solid sampling were checked at high emission levels of donor and acceptor dyes for various pump powers and acceptor-donor concentrations and were compared with theroretical results. To identify the thermal stability of solid pattern, the differential thermal analysis(DTA) and Thermogravimetric analysis(TGA) were performed. By adjusting the prism arrangement, for liquid and solid samples continuous tunability was observed from 570 to 727nm.

Optical limiting behavior of disperse red 1 dye doped polymer

Measurements of optical limiting response in disperse red 1 dye doped into ethylene propylene diene polymethylene polymer (EPDM) are reported using 532 nm wavelength, 10 ns pulses from a frequency-doubled Nd-YAG laser. The optical limiting behavior of the dye doped polymer was studied by transmission measurement technique at various concentrations. The results reveal that the optical limiting efficiency is dependent on concentration.

Optical limiting behavior of C 60 doped ethylenepropylenediene polymethylene polymer

Optical limiting measurements on C 60 in toluene–ethylenepropylenediene polymethylene (EPDM) polymer blends and in EPDM polymer films at three different concentrations have been carried out. The measurements were undertaken using 532 nm wavelength, 10 ns pulses from a frequency-doubled Nd-YAG Laser. The results show that the optical limiting efficiency is concentration dependent and that the limiting efficiency for C 60 in toluene–EPDM polymer blends is better than in EPDM polymer film samples.

Ferredoxin:NADP+ Oxidoreductase Association with Phycocyanin Modulates Its Properties

In photosynthetic organisms, ferredoxin:NADP(+) oxidoreductase (FNR) is known to provide NADPH for CO(2) assimilation, but it also utilizes NADPH to provide reduced ferredoxin. The cyanobacterium Synechocystis sp. strain PCC6803 produces two FNR isoforms, a small one (FNR(S)) similar to the one found in plant plastids and a large one (FNR(L)) that is associated with the phycobilisome, a light-harvesting complex. Here we show that a mutant lacking FNR(L) exhibits a higher NADP(+)/NADPH ratio. We also purified to homogeneity a phycobilisome subcomplex comprising FNR(L,) named FNR(L)-PC. The enzymatic activities of FNR(L)-PC were compared with those of FNR(S). During NADPH oxidation, FNR(L)-PC exhibits a 30% decrease in the Michaelis constant K(m)((NADPH)), and a 70% increase in K(m)((ferredoxin)), which is in agreement with its predicted lower activity of ferredoxin reduction. During NADP(+) reduction, the FNR(L)-PC shows a 29/43% decrease in the rate of single electron transfer from reduced ferredoxin in the presence/absence of NADP(+). The increase in K(m)((ferredoxin)) and the rate decrease of single reduction are attributed to steric hindrance by the phycocyanin moiety of FNR(L)-PC. Both isoforms are capable of catalyzing the NADP(+) reduction under multiple turnover conditions. Furthermore, we obtained evidence that, under high ionic strength conditions, electron transfer from reduced ferredoxin is rate limiting during this process. The differences that we observe might not fully explain the in vivo properties of the Synechocystis mutants expressing only one of the isoforms. Therefore, we advocate that FNR localization and/or substrates availability are essential in vivo.

Single Nanoobjects as Triggered Single Photons Sources

The generation of non-classical states of light [1] is an important scientific challenge with many potential applications. For example, squeezed states of light [2] have generated much interest in the past decade, because measurements can be performed with noise levels that are lower than those available with classical light. A particularly novel non-classical source of light is a triggered single-photon source: a source that has the property to emit with a high degree of certainty one (and only one) photon at a user-specified time. Such a deterministic source of single photons can be important for quantum information processing [3], quantum cryptography [4] and certain quantum computation problems [5]. A single quantum emitter such as a molecule or an atom is a good potential source because it can emit only one photon at a time. The emitted light is antibunched [6, 7] and consists of single photons separated by random time intervals, which depend on the excited state lifetime and on the pumping rate. Thus triggered emission of single photons can be obtained with controlled excitation of a single emitter. The first demonstration of a single photons source [8] using a single molecule in a solid is based on a rapid adiabatic passage method [9] to excite the molecule. In the effective spin picture, the Bloch vector follows the driving magnetic field adiabatically if the laser-molecule frequency detuning is swept slowly through the resonance. Since the passage inverts the field, the system goes from the ground to the excited state. From this fluorescent state the molecule can emit only a single photon. The molecular resonance is swept by Stark effect at fixed laser frequency. This is done easily by applying a radio frequency electric field to the molecule. The results showed photon states with statistics that differ radically from those of coherent states. But this method requires cryogenic temperatures (2K) since narrow zero phonon lines are needed for the adiabatic following. At room temperature a source of triggered single photons based on the concept of pulsed optical excitation of a single highly fluorescent molecule has been demonstrated [10]. A short pulse of green laser light pumps the molecule from the ground state to a vibronically excited level of the first electronic excited state. After fast (ps) relaxation to the lowest electronic excited state, the molecule subsequently emits a single photon. A frequency-doubled mode-locked Nd-YAG laser is used to pump highly stable single terrylene molecules contained in a p-terphenyl molecular crystal where they are protected from exposure to diffusing quenchers (such as oxygen). The result shows that the photons are emitted after the laser pulses at times separated by the laser repetition time within the lifetime of terrylene in p-terphenyl. Since the pump pulse width is very short compared to the fluorescence lifetime, the probability of two (or more) photon emission per pulse is always zero. At the maximum laser power, 90% of the laser pulses lead to a single photon emission. The parameters of this source (repetition rate and single photon generation probability) were limited only by the laser system used; nevertheless, this performance already surpasses that of previous work. The high performance combined with the vanishing two photon emission probability and the simplicity of this source suggests that it can be considered for a variety of quantum optical experiments and for secure quantum cryptography [11]. Semiconductor quantum dots (QD) are other potential systems for single photon generation [12]. QDs are often referred to as “artificial atoms” because many of their optical properties, such as ultranarrow transitions, arise from discrete, atomic-like energy levels [13, 14]. To reinforce this analogy a study of the photon antibunching in this system was needed. QDs differ from atoms and molecules since the creation of multiple excitons is possible in QDs. Consequently, if two electron-hole pairs can radiatively recombine, the simultaneous emission of two photons from a QD is then possible. Thus different regimes of photon statistics were expected because the probability of multiple exciton creation depends on excitation intensity. The fluorescence intensity correlation function of a single CdSe quantum dot has been investigated [15] using a coincidence setup (start-stop experiment). A strong photon antibunching has been observed over a large range of intensities (0.1-100 kW/cm2). The lack of coincidence at zero time delay indicates a highly efficient Auger ionization process [16], which suppresses multi-photon emission in these colloidal quantum dots. This result shows that room temperature single photon sources can be achieved with colloidal nanoparticles.

Characterization of Degenerate Four-Wave Mixing in Photorefractive Polymer-Dissolved Liquid Crystal Composites

Optical phase conjugation in a high-performance photorefractive polymer-dissolved liquid crystal composite has been observed with a cw frequency-doubled Nd-YAG laser (532 nm) or He–Ne laser (633 nm). The degenerate four-wave mixing experiment enabled measurements of phase conjugate reflectance as a function of input beam intensities, applied electric field, and grating spacing. The refractive index modulation was estimated from the phase conjugate reflectance on the basis of the coupled wave theory including the absorption loss of the photorefractive media. Small input powers were sufficient for inducing a large refractive index modulation around 4.0 ×10-3.

Photoexcitation in thin films deposited on silicon substrates by reactive pulsed laser ablation

Reactive pulsed laser ablation is a very interesting method to deposit thin films of several materials and compounds such as oxides, nitrides, semiconductors and superconductors. This technique relies on photoablation of pure elements, or a mixture of materials, with simultaneous exposure to a reactive atmosphere. In the case of oxides, reactions between the laser vaporized metals and oxygen lead to the formation of intermediate complexes and finally to oxide thin films. The reactivity of the plume has been already studied by our group in other oxides and nitrides productions and ascertained by Time of Flight Mass Spectrometry measurements [1].Thin films of semiconducting oxides such as In2O3, SnO2, and multilayers of these two compounds have been deposited by Reactive Pulsed Laser Ablation, with the aim to evaluate the behaviour of such films under variable halogen lamp illumination.Deposition of these thin films has been carried out by a frequency doubled Nd‐YAG laser (wavelength = 532 nm) on Silicon (100) substrates. A comparison, among indium oxide, tin oxide, and multilayers of indium and tin oxides, has been performed. The influence of physical parameters, such as substrate temperature and oxygen pressure in the deposition chamber, has been investigated. The deposited films have been characterized by Electric Resistance measurements.

Electrical and optical characterization of multilayered thin film based on pulsed laser deposition of metal oxides

Thin films of semiconducting oxides such as In2O3, SnO2, and multilayers of these two compounds have been deposited by reactive pulsed laser ablation, with the aim to produce toxic gas sensors. Deposition of these thin films has been carried out by a frequency doubled Nd-YAG laser (λ=532nm) on silicon (100) substrates. A comparison, among indium oxide, tin oxide, and multilayers of indium and tin oxides, has been performed. The influence of physical parameters such as substrate temperature, laser fluence and oxygen pressure in the deposition chamber has been investigated. The deposited films have been characterized by X-ray diffraction (XRD), optical and electric resistance measurements.

Holographic Bragg grating generation in photorefractive polymer-dissolved liquid-crystal composites

A large optical nonlinearity of n2=0.57 cm2/W in photorefractive mesogenic composites was achieved with low applied dc fields (0.30 V/μm) and a fringe spacing of 2.8 μm. The resultant diffraction efficiency from the Bragg gratings, which were written by a less intense laser (frequency-doubled Nd-YAG laser with a 532 nm wavelength), was around 39%. The limiting factors underlying these nonlinearities and their dynamics are also discussed.

Sensors based on pulsed laser deposition of multilayers of metal oxides

Pulsed laser ablation has been utilized in our laboratory to deposit thin films of semiconducting oxides such as indium oxide and tin oxide. Deposition of these thin films has been carried out by a frequency doubled Nd-YAG laser ( λ=532 nm) on silicon (100) substrates. A comparison has been performed, among indium oxide, tin oxide, and multilayers of indium and tin oxides, to evaluate their use as NO gas sensors. The influence of physical parameters, such as substrate temperature and laser fluence, on the velocity response of the films and on their resistance variation, has been investigated. The deposited films have been characterized by X-ray diffraction (XRD) and electric resistance measurements.

Indium and tin oxide polycrystalline thin films as NO gas sensors produced by reactive pulsed laser ablation and deposition

Pulsed laser ablation is a very interesting method of depositing thin films of several materials and compounds, such as oxides, nitrides, insulators, semiconductors, and superconductors. Indium and tin oxide polycrystalline thin films have been grown on silicon (100) substrates by reactive PLD from two metallic targets of indium and tin by multilayered deposition, in the presence of oxygen, using a frequency-doubled Nd-YAG laser (λ=532 nm). The films produced have been studied to evaluate their use as NO gas sensors, and the best performance has been found by varying some important parameters, such as the substrate temperature and the pressure of oxygen in the deposition chamber. X-ray diffraction analysis of the deposited films shows that they are polycrystalline with a preferential (400) orientation. Electrical resistivity measurements, performed by using a four-point probe technique, show a sharp increase in resistivity when the films are exposed to NO. The electrical responses of tin oxide-indium oxide multilayered thin films are reported.

Laser properties of pyrromethene dyes in sol–gel glasses

Solid-state dye lasers were made by incorporating pyrromethene dyes in organically modified silicate (ormosil) and composite glass matrices. Three different types of pyrromethene (PM) were used: PM 567, PM 580 and PM 597. The ormosil glass samples were prepared by a one-step process at room temperature sol–gel technology which led to the formation of hybrid organic/inorganic materials. The composite glass samples are made by a biphase process: (a) preparation of porous silica gel, (b) impregnation of the dye dissolved in methylmethacrylate (MMA) into the silica gel. A number of various glass compositions were tested and their efficiencies and half output energy lifetimes were measured. The optimal slope efficiency for the lasers pumped transversally, by frequency doubled Nd-Yag laser, approaches 42%. Fluorescence lifetimes, excitation and emission spectra were also measured. In addition, significant dependency of these dyes on pH was found. These dyes lose their lasing ability in acidic (pH < 3) surroundings. This must be considered in the sample preparation.

Starting Process of Laser-Triggered Vacuum Arc Ion Source

A laser-triggering method was applied to a vacuum arc ion source to improve triggering reliability. A frequency-doubled Nd-YAG laser was focused onto the arc cathode at a laser power density of (4.5–6.1)×108 W/cm2. Time-resolved observations revealed that a cathode spot was initially formed within the laser focusing area and the distribution of the cathode spots expanded circularly with time because of the retrograde motion of each cathode spot. The mean square displacement of the retrograde cathode spot was found to be proportional to the discharge time. Moreover, arc ignition probability with the laser trigger was measured under various conditions. It was found that the ignition probability strongly depends on the laser intensity and the gap spacing. This paper discusses the starting process of the laser-triggered vacuum arc discharge on the basis of the experimental results.

Two-dimensional imaging of soot volume fractions, particle number densities, and particle radii in laminar and turbulent diffusion flames

A two-dimensional optical technique has been developed to measure absolute soot volume fractions, particle number densities, and mean particle radii in moderately sooting laminar and turbulent diffusion flames. The RAYLIX technique is based on the two-dimensional detection of Rayleigh scattering and the laser-induced incandescence (LII) signal in combination with the detection of the extinction from one single laser pulse. For this, the beam of a frequency-doubled Nd-YAG laser is split into a low-energy beam and a high-energy beam and then expanded into a light sheet. The high-energy beam is delayed by about 20 ns by means of an optical delay line. The low-energy beam is used for Rayleigh scattering as well as for measuring the extinction. Scattering and extinction are simultaneously detected by a single-imageintensified charge-couple device (CCD) camera. The delayed high-energy beam passes the flame and induces the LII signal, which is detected by a second CCD camera. From these signals, two-dimensional fields of soot volume fractions (fv), particle number densities (Nv), and particle radii (rm) are derived. The profiles of the soot volume fractions, particle number densities, and mean particle radii for laminar flames exhibit maxima in the particle number density at radial positions, where minima in the particle radii were found, whereas the maxima in the soot volume fractions were shifted somewhat toward lower radical distances. This remains the case also for the turbulent flame, indicating that the timescales for soot formation are smaller than the turbulent timescales.

Are copper vapour and frequency doubled Nd:YAG lasers superior to the argon laser for portwine stains at pulse widths of 30–50 milliseconds?

Background and Objective The copper vapour laser (CVL) and the frequency doubled Nd:YAG laser (FDNYL) have been increasingly adopted as alternatives to the argon laser for treating vascular skin lesions. Automated scanning devices that permit the use of any of these lasers at 30–50 ms pulse widths are now widely used. The object of this study was to compare the CVL and FDNYL with the argon laser using pulse widths in the 30–50 ms range. Study Design/Materials and Methods Thirty-one adult patients with red-purple or purple portwine stains (PWS) were treated with a CVL at 578 nm, a FDNYL at 532 nm, and an argon laser at 488/514 nm. Test areas were performed using a Hexascan delivery system and an energy fluence just sufficient to produce immediate tissue change. Pulse widths were maintained constant for each patient (mean 40 msec). The mean fluences used were 13.1 J/cm2, 13.2 J/cm2, and 13.0 J/cm2, respectively. Assessments were made after 4 months using a clinical fading score and an index of light absorbence derived from reflectance spectrophotometry. Results Fading scores were statistically significantly better with the CVL (score = 2.29) than the FDNYL (score = 1.83, P < 0.02) and the argon laser (score = 1.89, P < 0.003). The differences between the FDNYL and the argon laser were not significant. Although there was a trend toward lower light absorbence index with the CVL than the argon laser and FDNYL (scores = 177, 179 and 181, respectively), these differences were not statistically significant. Conclusions Despite slightly better results with the CVL in terms of the fading produced, differences among the CVL, FDNYL, and argon lasers are small when 30–50 ms pulse widths are employed and are of doubtful clinical significance for darker PWS. © 1996 Wiley-Liss, Inc.

Are copper vapour and frequency doubled Nd:YAG lasers superior to the argon laser for portwine stains at pulse widths of 30–50 milliseconds?

The copper vapour laser (CVL) and the frequency doubled Nd:YAG laser (FDNYL) have been increasingly adopted as alternatives to the argon laser for treating vascular skin lesions. Automated scanning devices that permit the use of any of these lasers at 30-50 ms pulse widths are now widely used. The object of this study was to compare the CVL and FDNYL with the argon laser using pulse widths in the 30-50 ms range. Thirty-one adult patients with red-purple or purple portwine stains (PWS) were treated with a CVL at 578 nm, a FDNYL at 532 nm, and an argon laser at 488/514 nm. Test areas were performed using a Hexascan delivery system and an energy fluence just sufficient to produce immediate tissue change. Pulse widths were maintained constant for each patient (mean 40 msec). The mean fluences used were 13.1 J/cm2, 13.2 J/cm2, and 13.0 J/cm2, respectively. Assessments were made after 4 months using a clinical fading score and an index of light absorbence derived from reflectance spectrophotometry. Fading scores were statistically significantly better with the CVL (score = 2.29) than the FDNYL (score = 1.83, P < 0.02) and the argon laser (score = 1.89, P < 0.003). The differences between the FDNYL and the argon laser were not significant. Although there was a trend toward lower light absorbence index with the CVL than the argon laser and FDNYL (scores = 177, 179 and 181, respectively), these differences were not statistically significant. Despite slightly better results with the CVL in terms of the fading produced, differences among the CVL, FDNYL, and argon lasers are small when 30-50 ms pulse widths are employed and are of doubtful clinical significance for darker PWS.

Evaluation of frequency doubled Nd-Yag versus krypton red laser for photocoagulation of extra foveal and juxta foveal choroidal neovascularization due to age related maculopathy (A.M.D.)

Evaluation of frequency doubled Nd-Yag versus krypton red laser for photocoagulation of extra foveal and juxta foveal choroidal neovascularization due to age related maculopathy (A.M.D.)

4125 Evaluation of frequency doubled ND-YAG versus krypton red laser for photocoagulation of extra foveal and juxta foveal chroidal neovascularization due to age related maculopathy (A.M.D.)

4125 Evaluation of frequency doubled ND-YAG versus krypton red laser for photocoagulation of extra foveal and juxta foveal chroidal neovascularization due to age related maculopathy (A.M.D.)

Signature of the Weak Bond-Dangling Bond Conversion Process in a-Si:H as Seen by Total Photoelectron Yield Spectroscopy

Photoelectron Yield Spectroscopy is one of the most direct methods to study the density of gap states of amorphous semiconductors. We have made use of it to investigate the transient changes of the density of gap states of a-Si:H upon illumination with above-band-gap light. An excitation density of 50 mW/cm2 of 532 nm light from a frequency doubled Nd-YAG laser was modulated with frequencies between 0.1 Hz and 10 KHz and the transient response of the photoelectron yield signal was monitored by gated electron counting or a lock-in amplifier. From this we deduce a reversible increase of the occupied density of defect states under illumination with a maximum Δg ∼ 1017 cm3 eV-1 at about 0.3 eV below the Fermi energy and a decrease below EF− 0.75 eV, i. e. in the region of deep tail states. The effect exhibits a wide spectrum of time constants involved. Based on additional transient surface photo voltage measurements as well as numerical simulations we argue that the observed redistribution of states is not due to a light induced change in surface band bending or due to a mere excitation of electrons from occupied to empty states. Instead, we interpret the observed effect as a conversion of weak to dangling bonds, i.e. a precursor of the Staebler-Wronski Effect, lacking however the final step of hydrogen stabilisation necessary for the creation of metastable defects.