Optical Probe Method Research Articles

ICONE15-10175 Measurement technique of surface tension using a Single-Tip Optical fiber Probe

An optical fiber probe method is one of the efficient and reliable measurement methods for gas-liquid two-phase flows. Generally, simultaneous measurement of bubble diameters and velocities has been thought to need at least two optical fiber probes. To break through this situation, we newly developed a Single-Tip Optical fiber Probe (S-TOP) which realizes simultaneous measurement of diameters and velocities of minute bubbles/droplets. In the S-TOP measurement, the surface tension intensively influences the S-TOP signals. The main aim of this investigation is to strictly evaluate the influences of surface tension on the bubble measurement in order to develop the S-TOP which can take the surface tension into consideration. In the present study, we found out that the gradient of leading edge (or trailing edge) of the S-TOP signal is proportional to the gas-liquid interface velocity. In the measurement of gas-liquid interface velocity via S-TOP, this relationship is effectively utilized. The influences of surface tension and probe-surface wettability on this relationship were discussed. The gradients of the leading and trailing edges were changed with decrease in surface tension. At surface tension higher than about 50mN/m, the surface tension is dominant. On the other hand, at lower than this value, wettability is dominant.

Wavelength selective photoexcitation of picosecond acoustic-phonon pulses in a triple GaAs/Al 0.3Ga 0.7As quantum well structure

Ultrashort coherent phonon-pulse generation and detection is investigated in a GaAs–Al 0.3Ga 0.7As quantum well structure containing three wells of different widths using an optical pump and probe method. The pump photon energy is tuned to the region of the hh1– e1 transition energies of the wells and the probe photon energy is chosen for detection of the phonon pulses that reach the sample surface. By studying the dependence of the probe reflectance change on the pump photon energy, we demonstrate the possibility of wavelength-selective excitation of picosecond acoustic-phonon pulses in quantum wells.

EXPERIMENTAL STUDY ON PRESSURE FLUCTUATIONS IN HORIZONTAL AIR-WATER TWO-PHASE FLOW WITH AIR HAMMER PHENOMENON

Air entrained phenomena can often occur in hydraulic structures, for exmaple, headtank spillway of hydro power plant, intake channel, outlet channel, underground rivers, and so on. When the air goes out into the water surface of the outlet, the shock and the noise happen, and the structures may be destroyed at the critical moment. However, these are not enough studied. This study is an experimental investigation for pressure fluctuations created by the two-phase flow of air and water in a horizontal pipe, 100mm ID, on free outlet condition and water surface outlet condition. Measurements are also presented for the local void fraction, the local air velocity, and the local large bubble length using Optical Dual Probe Method. The effect of the outlet conditions was clarified on the pressure fluctuations at multi

Effect of Clearance between Two Sensor-Probes on Measured Values of Bubble Properties in a Bubble Column.

The effect of probe clearance on the rising velocity and chord length of bubbles in a bubble column was examined in measurements with the two-channel U-shaped optical fiber probe method. The probe clearances ranged from 0.2 to 1.5 cm. A few restrictions required in the signal processing to obtain the reasonable data. With increasing probe clearance, the observed values of the bubble velocities slightly increase; however, those of the bubble chord lengths drastically increase to 160% in the coalesced bubble regime, though they are almost constant in the dispersed bubble regime. A simple theory is proposed considering the probability of bubbles contacting with the probes, and used to successfully explain the experimental results.

A biased optical probe method for measurements of electron energy distribution in a plasma

A biased optical probe (BOP) method, i.e. novel technique for measurements of the electron energy distribution function (EEDF) in a range of such high energies as 10-50 eV has been developed. This method is based on the optical emission induced by electrons passing through a negatively biased mesh in a plasma. The BOP method was used to measure the EEDF in a DC glow discharge in He/Xe mixture while the low-energy part (<10 eV) of the EEDF was measured using the conventional Druyvesteyn method. The measured distribution function considerably deviates from an ideal Maxwellian distribution, because of abundant high-energy electrons generated in a cathode fall. On the contrary, the EEDF measured in a low-pressure inductive RF discharge was found to follow a single Maxwellian distribution over a wide energy range.

Simulation of photothermally diffused images and a concept of holoscan in photoacoustic and optical-probe imaging

Signals for gas-microphone photoacoustic (PA) and optical-probe methods are analyzed, and images for both cases are calculated and displayed. A one-dimensional theory is extended to include both schemes with a two-dimensional arrangement. An image of the optical-probe method shows higher definition than the gas-microphone PA method. Furthermore, a concept of a holoscan, which is applicable to not only PA imaging but generally also to scanned-image microscopy, is introduced to imaging science. Amplitude, phase, and holoscan images for both schemes are calculated; as a result, holoscan images show clearer edges at corners of a sample in both cases. Finally, images processed by deconvolution show higher fidelity in both schemes.

Domains in ferroelectric VDF/TrFE copolymer thin films: Investigated by a new optical probe method

Abstract A new optical probe method was developed by using electro-optic and piezoelectric effects and a phase sensitive detection to determine the polarization of domains in ferroelectric thin films. Ferroelectric domains within a region smaller than 1 μm were detected in annealed VDF(65)/TrFE(35) copolymer thin films. The switching dynamics of these individual domains were also investigated by using this method.

Heating and melting of single-crystal germanium by nanosecond laser pulses

The optical probe method was used in a study of melting of single-crystal germanium by nanosecond ruby laser pulses. A numerical simulation of the investigated thermal processes was carried out. The results of such simulation were compared with the experimental data. The characteristics of the behavior of the reflectivity of the liquid phase during heating by laser radiation were determined.

The Diffuse Vacuum Arc: A Definition

It is shown that the name diffuse arc based on high-speed photography is ambiguous. An optical-probe method is described, which enables one to quantify the arcing state. This leads to a new measurable quantity: diffusity.

Properties of Excited Surface-Wave Domains in CdS

The round-trip surface-wave domains are generated on the basal plane of CdS by exciting a surface wave externally. The effect of a transparent adhesive tape and observation by an optical probe method prove these domains to be surface-wave domains. The domain properties are controlled by the excited wave. That is, the excited domain has a narrower spectrum width than the spontaneous domain, and the fmax of the excited domain shifts to the first subharmonic frequency of the excited wave regardless of the carrier density of the sample. The excited wave, the strain of which is greater than 10-5, amplifies surface waves having frequencies near its first subharmonic by the nonlinear interaction through space charges. Then these waves are amplified further by the interaction with drifting electrons, and build up the full-grown excited domain.

Observation of Propagating Domain in Semiconductive CdS Using the Optical Probe Method

The optical modulation has been observed in semiconductive CdS single crystals at room temperature by means of the optical probe method using a monochromatic light. The light transmitted through materials with a wavelength corresponding to the intrinsic absorption edge was strongly modulated. The optical modulation observed here is caused primarily by the acoustic flux rather than by the high electric field in the domain. The acoustic domain arrives at its full growth near the point 2 mm from the cathode and travels towards the anode. The aspect of the acoustic domain is subjected to the variation by the strength of the applied electric field, and the domain velocity varies from 2.2×105 cm/sec to 3.0×105 cm/sec according to the increasing applied electric field up to 3040 V/cm.

Magnetic Domains by the Longitudinal Kerr Effect

Rotation of the polarization plane of obliquely incident light reflected from a polished ferromagnetic surface is successfully employed to reveal the antiparallel domains lying in the surface of a large single crystal of silicon iron. This Kerr magneto-optic effect is the basis of two methods of domain observation which are described in detail: (1) the optical probe method in which a small, focused beam of plane polarized light scans the crystal surface before being reflected into a photomultiplier tube located behind the Nicol prism analyzer, and (2) the photographic method in which the crystal surface is broadly illuminated with polarized light and the reflected beam is photographically recorded after passage through the analyzer. The truly saturated character of the domains is demonstrated, and the directions of the domains are assigned without ambiguity. Domain wall movement and Barkhausen discontinuities are revealed in photographs taken as the crystal is subjected to a changing magnetizing field. Possible applications and limitations of the method are discussed.