Transient Probe Research Articles

Optical Stark Effect and Coherent Gain of Excitons in a Semiconductor Microcavity

We report transient sub-picosecond pump and probe experiments performed on a semiconductor microcavity into which quantum wells have been inserted. The cavity is featuring resonance and strong coupling with the exciton. It is strongly and resonantly excited. Optical amplification of the probe beam (up to a factor of 5) appears, a blueshift of the polaritons occurs once the excitation reaches the exciton saturation density. The intensity of the probe, reflected or transmitted by the sample, oscillates while the pump to probe delay is varied. The frequency of the beats increases with pump intensity, and at the highest pumping rates it exceeds by far the frequency corresponding to the unperturbed Rabi splitting. This increase of the Rabi frequency is discussed in terms of the dynamical Stark shift of the excitons, while the amplification of the probe is qualitatively described as a coherent energy exchange between pump, excitons and probe.

Effect of sol-gel processing parameters on thermal properties of silica aerogels

The dependence of thermal conductivity (λ) and heat capacity per unit volume ( ρC p) of silica aerogels on the sol-gel processing parameters for a fixed temperature ranging from 300 to 360 K have been studied. The silica aerogels were made in circular shapes by varying one of the three molar ratios of ammonia (NH 4OH) /tetramethoxysilane(TMOS), methanol (MeOH) /TMOS and water (H 2O) /TMOS by keeping the other two molar ratios constant. The measurements were performed by using transient hot-wire probe method. The variation of NH 4OH/ TMOS molar ratio resulted in a slow change in λ and ρC p values whereas MeOH/TMOS and H 2O/TMOS molar ratios resulted in marked changes as a function of temperature. The results have been discussed by taking into account of the chemistry and the resulting porosities of the aerogels.

Enthalpy, Heat Capacity and Thermal Conductivity of Boneless Mutton between −40 and +40 °C

The thermal properties of boneless lamb meat were determined in a temperature range usually encountered in both freezing and refrigeration processes. The specific heat and the enthalpy were measured by differential scanning calorimetry (DSC) while thermal conductivity was measured by the transient probe method. Values thus measured were compared with predictive equations from the literature. Also, experimental data of thermal properties were mathematically interpreted as a function of temperature by fitting simple predictive equations to them.

Internal toroidal field measurements on the helicity injected tokamak using the transient internal probe

Measurements of the local toroidal magnetic field have been achieved on the helicity injected tokamak (HIT) using the transient internal probe (TIP). HIT is a low aspect (a=1.5, R=0.35 m) ratio tokamak designed to study steady state current drive. The TIP diagnostic involves accelerating a small diamond clad magneto-optic probe through the plasma at high velocities (∼2 km/s) using a light gas gun. The local field is obtained by illuminating the probe with a laser and measuring the amount of Faraday rotation in the reflected beam. Measurements were conducted using unclad magneto-optic probes directed along a chord tangent to the toroidal field. Plasma conditions were typically ne∼7×1019 m−3 and Te∼40–80 eV. Measurement uncertainty is less than 2%. No changes in plasma parameters were observed during the first 200 ms (∼40 cm) of probe travel in the plasma. A temporary dip in plasma current, probably due to ablation of the retroreflecting material on the probe, is observed as the probe exits the plasma. Density is unaffected by the presence of the probe in the plasma. No long term deleterious effects to tokamak performance were observed as the TIP diagnostic was found to be quite compatible with the tokamak.

The simultaneous measurement for thermal properties of liquids using transient probe method

The theoretical model for the transient probe method is the modified Jaeger model which is used perfect line source theory. The transient probe technique has been developed for the simultaneous determination of thermal conductivity, diffusivity and volumetric heat capacity of liquids. The Levenberg-Marquardt iteration method is adapted to obtain thermal property within nonlinear range. Experimental results of liquids were found to agree well with recommended thermal property data.

Extinguishing by “slow quenching’’ in a thick grid Cs–Ba tacitron

Transient Langmuir probe measurements of the plasma density, electron temperature, and plasma potential during “slow quenching’’ of a Cs–Ba tacitron at two different discharge conditions were made. Following the application of a negative voltage pulse on the grid, the grid aperture sheaths initially grew then shrank temporarily, due to an increase in the ion flux from the grid-collector region, then grew again until the discharge eventually extinguished. Discharge extinguishing occurred when the effective ionization cross section became decoupled from the continually rising electron temperature; hence, the discharge could not be maintained owing to the decrease in the ionization rate. This inability to maintain the discharge is considered the mechanism for extinguishing by slow quenching.

Magnetic field measurements using the transient internal probe (TIP)

The transient internal probe (TIP) is a novel diagnostic technique for measuring magnetic fields in hot plasmas. The concept involves shooting a diamond clad magneto-optic probe through the plasma at high velocity allowing measurement of the local magnetic field before ablation occurs. Magnetic field measurements are obtained by illuminating the probe with an argon laser and measuring the amount of Faraday rotation in the reflected light. The diagnostic was tested by measuring a permanent magnetic field inside a vacuum chamber with a probe traveling at 2 km/s using an unclad probe. The purpose of this experiment was to demonstrate the capability of the TIP diagnostic and to verify compatibility with plasma vacuum requirements. Magnetic field resolutions of 20 G and 1 cm spatial resolution were achieved. The response time of the detection system is 10 MHz. Introduction of a helium muzzle gas into the plasma chamber was limited to less than 0.4 Torr ℓ.

Prediction and analysis of transient eddy-current probe signals : Bowler, J.R. Review of Progress in Quantitative Nondestructive Evaluation, Brunswick, Maine (United States), 23–28 Jul. 1989. Vol. 9A, pp. 287–293. Edited by D.O. Thompson and D.E. Chimenti. Plenum Press (1990)

Prediction and analysis of transient eddy-current probe signals : Bowler, J.R. Review of Progress in Quantitative Nondestructive Evaluation, Brunswick, Maine (United States), 23–28 Jul. 1989. Vol. 9A, pp. 287–293. Edited by D.O. Thompson and D.E. Chimenti. Plenum Press (1990)

The transient internal probe: A novel method for measuring internal magnetic field profilesa)

The transient internal probe (TIP) diagnostic is designed to permit internal magnetic field measurements in hot, high density plasmas. A small probe is fired through the plasma at high velocities and magnetic field measurements are accomplished using Faraday rotation within the Verdet glass probe. Magnetic field resolution of ±40 G and spatial resolution of 5 mm have been achieved. System frequency response is 10 MHz. Ablative effects are avoided by minimizing both the probe size and the time the probe spends in the plasma. A two-stage light-gas gun is used to accelerate the probe (held by a sabot) to 2.2 km/s. The sabot is removed using gas dynamic forces and a gas interface system prevents the helium muzzle gas from entering the plasma chamber. Work is underway to integrate the TIP diagnostic with laboratory plasma experiments.

Polyphasic rise of chlorophyll a fluorescence in herbicide-resistant D1 mutants of Chlamydomonas reinardtii

Chlorophyll (Chl) a fluorescence transient, a sensitive and non-invasive probe of the kinetics and heterogeneity of the filling up of the electron acceptor pool of Photosystem II (PS II), was used to characterize D1-mutants of Chlamydomonas reinhardtii. Using a shutter-less system (Plant Efficiency Analyzer, Hansatech, UK), which provides the first measured data point at 10 μs and allows data accumulation over several orders of magnitude of time, we have characterized, for the first time, complete Chl a fluorescence transients of wild type (WT), cell wall less (CW-15) C. reinhardtii and several herbicide-resistant mutants of the D1 proteins: D1-V219I The mutants are labeled as follows: the single letter code for the wild type amino acid, followed by the residue number, then the code for the mutated amino acid. A251V, F255Y, S264A G256D and L275F. In all cases, the Chl a fluorescence induction transients follow a pattern of O-J-I-P where J and I appear as two steps between the minimum Fo (O) and the maximum Fmax (Fm, P) levels. The differences among the mutants are in the kinetics of the filling up of the electron acceptor pool of PS II (this paper) in addition to those in the re-oxidation kinetics of QA (-) to QA, published elsewhere (Govindjee et al. (1992) Biochim Biophys. Acta: 1101: 353-358; Strasser et al. (1992) Archs. Sci. Genève 42: 207-224) and not in the ratio of the maximal fluorescence Fm to the initial fluorescence Fo. The value of this experimental ratio is Fm/Fo = 4.4±0.21 independent of the mutation. At 600 W m(-2) of 650 nm excitation, distinct hierarchy in the fraction of variable Chl a fluorescence at the J level is observed: S264A > A251V ∼ G256A > L275F ∼ V219I > F255Y ∼ CW-15 ∼ WT. At 300 and 60 W m(-2) excitation, a somewhat similar hierarchy among the mutants was observed for the intermediate levels J and I. Addition of bicarbonate-reversible inhibitor formate did not change the O to J phases, slowed the I to P rise, and in many cases, slowed the decay of fluorescence beyond the P level. These observations are interpreted in terms of formate effect being on the acceptor rather than on the donor side (S-states) of PS II. The formate effect was different in different mutants, with L275F being the most insensitive mutant followed by others (V219I, F255Y, WT, A251V and S264A). Further, in the presence of high concentrations of DCMU, identical transients were observed for all the mutants and the WT.The quantum yield of photochemistry of PS II, calculated from 1-(Fo/Fm), is in the range of 0.73 to 0.82 for the WT as well as for the mutants examined. Thus, in contrast to differences in the kinetics of the electron acceptor side of PS II, there were no significant differences in the maximum quantum yield of PS II, among the mutants tested. We suggest that earlier photochemistry yield values were much lower (0.4-0.6) than those reported here due to either higher measured values of Fo by instruments using camera shutters, or due to the use of cells grown in less than-optimal conditions.

The transient internal probe: A novel method for measuring internal magnetic field profiles (abstract)a)

The transient internal probe (TIP) diagnostic is designed to permit internal magnetic field measurements in hot, high density plasmas. A small probe is fired through the plasma at high velocities and magnetic field measurements are accomplished using Faraday rotation within the Verdet glass probe. Magnetic field resolution of ±40 G and spatial resolution of 5 mm have been achieved. System frequency response is 10 MHz. Ablative effects are avoided by minimizing both the probe size and the time the probe spends in the plasma. A two-stage light-gas gun is used to accelerate the probe (held by a sabot) to 2.2 km/s. The sabot is removed using gas dynamic forces and a gas interface system prevents the helium muzzle gas from entering the plasma chamber. Work is underway to integrate the TIP diagnostic with laboratory plasma experiments.

Thermal conductivity measurements in soil using an instrument based on the cylindrical probe method

The article discusses the underlying hypothesis, the limits, the range of application, and the practical operation of a versatile thermal conductivity analyzer based on a transient cylindrical probe method. The best expected precision for the conductivity determination appears to be ∼±10%. A compact analyzer, integrating all the apparatus’ components in the same unit, has been specifically designed for environmental research in the field. Calibration received special attention regarding thermal conductivity values in the range 0.1–3 W/mK. The analyzer was tested on seven materials, in field conditions, and discrepancies from published conductivity values did not exceed 9%. Several checks were performed in the laboratory to study the influence of experimental conditions, such as the probe insertion technique. The cylindrical probe method appears well suited to powdered materials, but may also be applied to viscous liquids and solid matter. As an application, the cylindrical probe was used to characterize nine soils from the Belgian Lorraine. After soil analysis in the dry state, thermal conductivity of each sample was determined at different moisture contents. The transient cylindrical probe method proved to be quick and easy, whether in situ or on samples in the laboratory. It is a powerful tool which can map a country’s soil thermal properties.

Dynamics of transient probe beam amplification via coherent multiwave mixing in a local nonlinear medium-nematic liquid crystal

The dynamics of the transient thermal-grating-mediated probe-beam amplification effect in a nematic liquid crystal film is studied with the use of millisecond laser pulses. These experimental observations and the accompanying transient multiwave mixing analysis show that peak probe gain can occur at various locations within the grating decay time; the higher the induced index change, the sooner will peak gain occur.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Determination of the thermal conductivities of building and insulating materials by the probe method

A simple and inexpensive electrical circuit based on the transient probe method has been developed for the determination of thermal conductivities of building and insulating materials namely limebrick, gypsum, rockwool and polystrene foam. The solution of the unsteady state heat conduction equation has been approximated by considering certain simplifying assumptions which have been justified by experimental observations. The overall accuracy of the thermal conductivity measurements is estimated to be within ± 3%.

Development of a transient internal probe diagnostic

The transient internal probe (TIP) diagnostic is a novel method for probing the interior of hot magnetic fusion plasmas. In the TIP scheme, a probe is fired, using a two-stage light gas gun, through a hot plasma at velocities up to 5 km/s, and makes direct, local measurements of the internal magnetic field structure. The data are relayed to the laboratory optical detection system using an incident laser that is directed through a Faraday rotator payload acting as a magneto-optic sensor. Ablative effects are avoided by minimizing the probe size, limiting the time that the probe is in the hot plasma, and encasing the probe with a diamond cladding. The degree to which the diamond probe cladding is susceptible to ablative effects will determine the plasma density and temperature regime in which the TIP diagnostic can be used. If the TIP suffers significant ablation it is an indication that the diagnostic is not usable on this hot and dense of a plasma (or that greater velocity must be imparted to the probe to further minimize the time that it is in the plasma). A quantitative experimental study of the ablation rates of diamond is planned as part of the TIP development. The integrated TIP system will be functional in 1992 and installed on the Helicity Injected Torus (HIT) [T. R. Jarboe, Fusion Tech. 15, 9 (1989)] at the University of Washington.

Experimental investigation on the thermophysical properties of moist porous materials

A method has been developed for the combined measurement of thermal conductivity and diffusivity. The proposed method is based on an extension of the transient probe theory. The developed technique, the differential sensor method, is then used here for the measurement of thermal conductivity and diffusivity of glycerin, dry and moist porous materials in the temperature range of –20 to 80°C. Calculations have been doneby IBM PC/XT using a data fitting program. The effect of water content and temperature on the thermophysical properties has been elucidated in frozen as well as unfrozen states. The experimental results of thermal conductivity and diffusivity obtained by the differential sensor method have been compared with the results of other methods.

Differential temperature sensors method for simultaneous determination of thermal conductivity and diffusivity

An attempt has been made to minimize the sources of error involved in the transient probe method for thermal conductivity determination. Two sensors (thermocouples) are mounted parallel to the needle probe at known distances. This modification makes it a device for simultaneous conductivity and diffusivity determination. Thermal conductivity and diffusivity for glycerine, dune sand and mustard seed are determined by this method. Results obtained are compared with those obtained by a calibrated transient probe for conductivity and by a parallel wire method for diffusivity. Analysis of the results prove it to be a better instrument over the traditional ones. The technique can also be used as a direct reading device for conductivity and diffusivity measurements.

Laser-induced thermal desorption of moisture from a surface in atmospheric conditions

Moisture adsorbed on a gold, copper, or silicon surface in atmospheric conditions can be detected by using a pulsed laser-induced heating of the surface (transient temperature rise ≲100 °C), and a continuous probe laser beam parallel to the surface to detect the transient refractive-index changes. The probe deflection signal can be interpreted as due to a compression pulse (produced by the heating and moisture desorption at the sample surface), followed by a rarefraction (produced by cooling and diffusional moisture readsorption). Using this interpretation of the transient probe deflection signal, the amount of moisture adsorbed at the samples for various surface temperatures and absolute moisture content in an ambient gas (e.g., nitrogen) can be monitored.

Experimental thermal diffusivities/conductivities of frozen media through stefan problem simulation

An experimental apparatus to perform soil-freezing experiments on liquid-sand systems is described. Temperature measurements along the specimen are carried out during the freezing, and the liquid content distribution is measured with the gravimetric method at the end of the process. Water and tert-amyl alcohol are used as liquids in the saturated sand. A liquid layer is maintained on top of the sand to provide a liquid reservoir. Some experiments have been done to reproduce the “Stefan problem”. From the relation between freezing front penetration and time, the thermal diffusivity has been evaluated. The thermal conductivity obtained is in agreement with the measurements performed on the same sand with the transient thermal probe method.

Transient probe spectra in a driven two-level atom.

We analyze the transient probe spectra that arise when two-level atoms in an atomic beam are excited by a ``pump'' laser field and are probed by a step-function weak field on the same atomic transition. The temporal relaxation of the probe spectra to their steady-state values is found to depend critically on the initial atom--pump-field dressed-state populations and coherences. The transient spectra may be composed of absorption-emission structure that is totally absent in the steady-state limit. A simple physical interpretation of the spectra is given in terms of a conventional dressed-atom picture. In addition, we study the effects of collisions on transient probe spectra and investigate the transient buildup of several collision-induced features in the spectra.