Emission and holographic interferometry measurements in a superorbital expansion tube

Free-piston-driven expansion tubes are capable of generating flaw conditions over a wide range of enthalpies ranging from orbital up to superorbital velocities. Initial optical measurements aimed at investigating the flow in such a facility are presented. Emission studies were used to identify impurities in the how and to investigate spectral regions that are accessible by optical techniques. At moderate enthalpies, it was found that significant radiation resulted from metallic contaminants. At high enthalpies, the spectrum consisted of a number of atomic lines together with a broadband background component indicative of the presence of electrons. The presence of this radiation may limit the applicability of optical techniques that require spectral regions free from the influence of atomic transitions or background radiation. Emission spectroscopy (through Stark broadened hydrogen lines) and two-wavelength holographic interferometry were used to measure the electron number density behind a bow shock on a blunt body at conditions where significant ionization was observed. They yielded average concentrations of (3 +/- 1) x 10(17) cm(-3) from the emission measurements and (3.8 +/- 0.6) x 10(17) cm(-3) from the interferometry.

Atoms in squeezed light fields

Squeezed light is of interest as an example of a non-classical state of the electromagnetic field and because of its applications both in technology and in fundamental quantum physics. This review concentrates on one aspect of squeezed light, namely its application in atomic spectroscopy. The general properties, detection and application of squeezed light are first reviewed. The basic features of the main theoretical methods (master equations, quantum Langevin equations, coupled systems) used to treat squeezed light spectroscopy are then outlined. The physics of squeezed light interactions with atomic systems is dealt with first for the simpler case of two-level atoms and then for the more complex situation of multi-level atoms and multi-atom systems. Finally the specific applications of squeezed light spectroscopy are reviewed.

Infrared seeded parametric four-wave mixing for sensitive detection of molecules

We have developed a sensitive resonant four-wave mixing technique based on two-photon parametric four-wave mixing with the addition of a phase matched ''seeder'' field. Generation of the seeder field via the same four-wave mixing process in a high pressure cell enables automatic phase matching to be achieved in a low pressure sample cell. This arrangement facilitates sensitive detection of complex molecular spectra by simply tuning the pump laser. We demonstrate the technique with the detection of nitric oxide down to concentrations more than 4 orders of magnitude below the capability of parametric four-wave mixing alone, with an estimated detection threshold of 10(12) molecules/cm(3).

Cavity QED analog of the harmonic-oscillator probability distribution function and quantum collapses

We establish a connection between the simple harmonic oscillator and a two-level atom interacting with resonant, quantized cavity and strong driving fields, which suggests an experiment to measure the harmonic-oscillator's probability distribution function. To achieve this, we calculate the Autler-Townes spectrum by coupling the system to a third level. We find that there are two different regions of the atomic dynamics depending on the ratio of the: Rabi frequency Omega (c) of the cavity field to that of the Rabi frequency Omega of the driving field. For Omega (c)

The damped and coherently-driven Jaynes-Cummings model

We investigate the influence of a single-mode cavity on the Autler-Townes doublet that arises when a three-level atom is strongly driven by a laser field tuned to one of the atomic transitions and probed by a tunable, weak field coupled to the other transition. We assume that the cavity mode is coupled to the driven transition and the cavity and laser frequencies are equal to the atomic transition frequency. We find that the Autler-Townes spectrum can have one, two or three peaks depending on the relative magnitudes of the Rabi frequencies of the cavity and driving fields. We show that, in order to understand the three-peaked spectrum, it is necessary to go beyond the secular approximation, leading to interesting quantum interference effects. We find that the positions and relative intensities of the three spectral components are affected strongly by the atom-cavity coupling strength g and the cavity damping K. For an increasing g and/or decreasing K the triplet evolves into a single peak. This results in 'undressing' of the system such that the atom collapses into its ground state. We interpret the spectral features in terms of the semiclassical dressed-atom model, and also provide complementary views of the cavity effects in terms of quantum Langevin equations and the fully quantized, 'double -dressing' model.

Arsenic and germanium determination by hydride generation in the D.C. plasma optical emission spectrometer

Modifications to the commercial hydride generator, manufactured by Spectrametrics, resulted in improved operating procedure and enhancement of the arsenic and germanium signals. Experiments with arsenic(III) and arsenic(V) showed that identical reiults could be produced from both oxidation states. However, since arsenic(V) is reduced more slowly than arsenic(III), peak areas and not peak heights must be measured when the arsine is immediately stripped from the system (approximately 5 seconds reaction). When the reduction is allowed to proceed for 20 seconds before the arsine is stripped, peak heights may be used. For a 200 ng/mL solution, the relative standard deviation is 2.8% for As(III) and 3.8% for As(V). The detection limit for arsenic using the modified system is 0.50 ng/mL. Studies performed on As(V) standards show that the interferences from 1000 mg/L of nickel(II), cobalt(II), iron(III), copper(II), cadmium(II), and zinc(II) can be eliminated with the aid of 5 M Hel and 3% L-cystine. Conditions for the reduction of germanium to the corresponding hydride were investigated. The effect of different concentrations of HCl on the reduction of germanium to the covalent hydride in aqueous media by means of NaBH 4 solutions was assessed. Results show that the best response is accomplished at a pH of 1.7. The use of buffer solutions was similarly characterized. In both cases, results showed that the element is best reduced when the final pH of the solution after reaction is almost neutral. In addition, a more sensitive method, which includes the use of (NH4)2S208' has been developed. A 20% increase in the germanium signal is registered when compared to the signal achieved with Hel alone. Moreover, under these conditions, reduction of germanium could be accomplished, even when the solution's pH is neutral. For a 100 ng/mL germanium standard the rsd is 3%. The detection limit for germanium in 0.05 M Hel medium (pH 1.7) is 0.10 ng/mL and 0.09 ng/mL when ammonium persulphate is used in conjunction with Hel. Interferences from 1000 mg/L of iron(III), copper(II), cobalt(II), nickel(II), cadmium(II), lead(II), mercury(II), aluminum(III), tin(IV), arsenic(III), arsenic(V) and zinc(II) were studied and characterized. In this regard, the use of (NH4)ZS20S and Hel at a pH of 1.7 proved to be a successful mixture in the sbppression of the interferences caused by iron, copper, aluminum, tin, lead, and arsenic. The method was applied to the determination of germanium in cherts and iron ores. In addition, experiments with tin(IV) showed that a 15% increase in the tin signal can be accomplished in the presence of 1 mL of (NH4)2S20S 10% (m/V).

Optical emission spectroscopic studies on laser ablated zinc oxide plasma

Optical emission spectroscopic studies were carried out on the plasma produced by ablation of zinc oxide target using the third harmonic 355 nm of Q-switched Nd:YAG laser, in vacuum and at three different ambient gas oxygen pressures. The spatial variations of electron density Ne and electron temperature Te were studied up to a distance of 20 mm from the target surface. The kinematics of the emitted particles and the expansion of the plume edge are discussed. The optimum conditions favorable for the formation of high quality zinc oxide thin films are thereby suggested.

Optical Emission Diagnostics Of Laser Produced Plasma From Graphite And Yba2cu3o7

This thesis is entitled “OPTICAL EMISSION DIAGNOSTICS OF LASER PRODUCED PLASMA FROM GRAPHITE AND YBa2Cu3O7. The work presented in this thesis covers the experimental results on the plasma produced with moderately high power laser with irradiance range in between 10 GW cm 2 to 100 GW cm -2. The characterization of laser produced plasma from solid targets viz. graphite and high temperature superconducting material like YBa2Cu3O7 have been carried out. The fundamental frequency from a Q - switched Nd: YAG laser with 9 ns pulse duration is used for the present studies. Various optical emission emission diagnostic techniques were employed for the the characterization of the LPP which include emission spectroscopy, time resolved studies, line broadening method etc. In order to understand the physical nature of the LPP like recombination, collisional excitation and the laser interaction with plasma, the time resolved studies offer the most logical approach

Time resolved study of CN band emission from plasma generated by laser irradiation of graphite

Time and space resolved studies of emission from CN molecules have been carried out in the plasma produced from graphite target by 1.06 urn pulses from a Q-switched Nd:YAG laser. Depending on the laser pulse energy, time of observation and position of the sampled volume of the plasma, the features of the emission spectrum are found to change drastically. The vibrational temperature and population distribution in the different vibrational levels have been studied as functions of distance, time, laser energy and ambient gas pressure. Evidence for nonlinear effects of the plasma medium such as self focusing which exhibits threshold-like behaviour are also obtained. Temperature and electron density of the plasma have been evaluated using the relative line intensities of successive ionization stages of carbon atom. These electron density measurements are verified by using Stark broadening method.

Emission characteristics and dynamics of C2 from laser produced graphite plasma

The emission features of laser ablated graphite plume generated in a helium ambient atmosphere have been investigated with time and space resolved plasma diagnostic technique. Time resolved optical emission spectroscopy is employed to reveal the velocity distribution of different species ejected during ablation. At lower values of laser fluences only a slowly propagating component of C2 is seen. At high fluences emission from C2 shows a twin peak distribution in time. The formation of an emission peak with diminished time delay giving an energetic peak at higher laser fluences is attributed to many body recombination. It is also observed that these double peaks get modified into triple peak time of flight distribution at distances greater than 16 mm from the target. The occurrence of multiple peaks in the C2 emission is mainly due to the delays caused from the different formation mechanism of C2 species. The velocity distribution of the faster peak exhibits an oscillating character with distance from the target surface.

Study of solvent effect in laser emission from Coumarin 540 dye solution

The results of a brief investigation of the amplified spontaneous emission and lasing characteristics of Coumarin 540 dye in as many as ten different solvents are reported. It has been found that C 540 dye solutions contained within a rectangular quartz cuvette give laser emission with well resolved equally spaced modes when pumped with a 476 nm beam. The modes were found to originate from the subcavities formed by the plane-parallel walls of the cuvette containing the high-gain medium. While the quantum yield remains a decisive factor, a clear correlation between the total width of the emission spectra and the refractive indices of the solvents of the respective samples has been demonstrated. The well-resolved mode structure exhibited by the emission spectra gives clear evidence of the lasing action taking place in the gain medium, and the number of modes enables us to compare the gain of the media in different samples. A detailed discussion of the solvent effect in the lasing characteristics of C540 in different solutions is given.

Ultrafast charge separation in a photoreactive rhenium-appended porphyrin assembly monitored by picosecond transient infrared spectroscopy

Rhenium(bipyridine)(tricarbonyl)(picoline) units have been linked covalently to tetraphenylmetalloporphyrins of magnesium and zinc via an amide bond between the bipyridine and one phenyl substituent of the porphyrin. The resulting complexes, abbreviated as [Re(CO)(3)(Pic)Bpy-MgTPP][OTf] and [Re(CO)(3)(Pic)Bpy-ZnTPP][OTf], exhibit no signs of electronic interaction between the Re(CO)(3)(bpy) units and the metalloporphyrin units in their ground states. However, emission spectroscopy reveals solvent-dependent quenching of porphyrin emission on irradiation into the long-wavelength absorption bands localized on the porphyrin. The characteristics of the excited states have been probed by picosecond time-resolved absorption (TRVIS) spectroscopy and time-resolved infrared (TRIR) spectroscopy in nitrile solvents. The presence of the charge-separated state involving electron transfer from MgTPP or ZnTPP to Re(bpy) is signaled in the TRIR spectra by a low-frequency shift in the nu(CO) bands of the Re(CO)(3) moiety similar to that observed by spectroelectrochemical reduction. Long-wavelength excitation of [Re(CO)(3)(Pic)Bpy-MTPP][OTf] results in characteristic TRVIS spectra of the S-1 state of the porphyrin that decay with a time constant of 17 ps (M = Mg) or 24 ps (M = Zn). The IR bands of the CS state appear on a time scale of less than 1 ps (Mg) or ca. 5 ps (Zn) and decay giving way to a vibrationally excited (i.e., hot) ground state via back electron transfer. The IR bands of the precursors recover with a time constant of 35 ps (Mg) or 55 ps (Zn). The short lifetimes of the charge-transfer states carry implications for the mechanism of reaction in the presence of triethylamine.

Evaluation of intramolecular energy transfer process in the lanthanide(III) bis- and tris-(TTA) complexes: Photoluminescent and triboluminescent behavior

This work reports the energy transfer mechanism process of [Eu(TTA)(2)(NO(3))(TPPO)(2)] (bis-TTA complex) and [Eu(TTA)(3)(TPPO)(2)] (tris-TTA complex) based on experimental and theoretical spectroscopic properties, where TTA = 2-thienoyltrifluoroacetone and TPPO = triphenylphosphine oxide. These complexes were synthesized and characterized by elemental analyses, infrared spectroscopy and thermogavimetric analysis. The theoretical complexes geometry data by using Sparkle model for the calculation of lanthanide complexes (SMLC) is in agreement with the crystalline structure determined by single-crystal X-ray diffraction analysis. The emission spectra for [Gd(TTA)(3)(TPPO)(2)] and [Gd(TTA)(2) (NO(3))(TPPO)(2)] complexes are associated to T -> S(0) transitions centered on coordinated TTA ligands. Experimental luminescent properties of the bis-TTA complex have been quantified through emission intensity parameters Omega(lambda)(lambda = 2 and 4), spontaneous emission rates (A(rad)), luminescence lifetime (tau), emission quantum efficiency (eta) and emission quantum yield (q), which were compared with those for tris-TTA complex. The experimental data showed that the intensity parameter value for bis-TTA complex is twice smaller than the one for tris-TTA complex, indicating the less polarizable chemical environment in the system containing nitrate ion. A good agreement between the theoretical and experimental quantum yields for both Eu(Ill) complexes was obtained. The triboluminescence (TL) of the [Eu(TTA)(2)(NO(3))(TPPO)(2)] complexes are discussed in terms of ligand-to-metal energy transfer. (c) 2007 Elsevier B.V. All fights reserved.

Study of Hybrid Silica-Polyethyleneglycol Xerogels by Eu3+ Luminescence Spectroscopy

Good optical quality Eu3+-doped silica-polyethyleneglycol hybrids were prepared by the sol-gel process. Thermomechanical analysis showed an increase of the glass transition temperature, due to the stiffness of the polymeric network, as the amount of Eu3+ increased. Europium luminescent properties were used to study structural evolution during the sol-gel transition. For lower doping concentrations dried gels present statistical distributions of Eu3+, typical of an amorphous environment, while for higher concentrations a crystalline-like environment of Eu3+ was observed. A broad emission band was observed in the visible part of the electromagnetic spectrum and assigned to the intrinsic emission from the hybrid polymeric network.

Analysis of modified bowtie nanoantennas in the excitation and emission regimes

In this work, we analyze modified bowtie nanoantennas with polynomial sides in the excitation and emission regimes. In the excitation regime, the antennas are illuminated by an incident plane wave, and in the emission regime, the excitation is fulfilled by infinitesimal electric dipole positioned in the gap of the nanoantennas. Several antennas with different sizes and polynomial order were numerically analyzed by method of moments. The results show that these novel antennas possess a controllable resonance by the polynomial order and good characteristics of near field enhancement and confinement for applications in enhancement of spontaneous emission of a single molecule.