Browsing by Author "PAN, RP"

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A QUANTITATIVE STUDY OF THE FAR-FIELD LASER-INDUCED RING PATTERN FROM NEMATIC LIQUID-CRYSTAL FILMS
(1992-08-01)
PAN, RP
;
CHEN, SM
;
PAN, CL
;
電子物理學系
;
光電工程學系
We report the first detailed measurement of multiple (up to twenty) diffraction rings due to a laser beam traversing a nematic liquid crystal cell. Experimental measured intensity distributions are in good agreements with numerical calculations based on the diffraction theory, taking into account the spatial self-phase modulation effect, the two-dimensionality of the problem, the wavefront curvature effect and the non-local response of the nematic liquid crystals. The individual contributions of the aforementioned effects on the far-field pattern are clearly illustrated.
ANALYSIS OF BEAM SIZE EFFECT ON THE LASER-INDUCED FREEDERICKSZ TRANSITION AND THE DYNAMIC-RESPONSE IN NEMATIC LIQUID-CRYSTAL (5CB) FILMS WITH A FREE-SURFACE
(1992-02-01)
CHEN, SM
;
PAN, RP
;
電子物理學系
;
光電工程學系
;
Department of Electrophysics
The non-local effect caused by the finite laser beam size in the laser induced Freedericksz transition for the homeotropically aligned nematic liquid crystal film is derived analytically and calculated numerically. The influences on the transition threshold and the dynamic response are discussed. The coupling between backflow effect and the non-local effect is shown to be important for the films with a free surface by the calculated results and by comparing with the existing experimental results.
DIELECTRIC-BREAKDOWN PATTERNS IN THIN-LAYERS OF OILS
(1995)
PAN, RP
;
SHEU, CR
;
LAM, L
;
電子物理學系
;
Department of Electrophysics
Experimental dielectric breakdown patterns are generated in thin cells of oils. Both mineral oil and olive oil are used. The cell is 6 mu m thick and consists of two glass plates with conductive coating on the inner surfaces. A dc voltage across the cell is either increased gradually to above the threshold or applied with a fixed value above the threshold. Different types of patterns due to chemical reactions occurring at the inner surfaces are left behind after the dielectric breakdown process takes place. These patterns consist of filaments with wiggling or winding, depending on the experimental conditions. Time variations of the voltage and current are recorded during and after the discharge process. Some of these patterns are compared with those generated by the active walker model. The physical processes behind these patterns are discussed.
DOUBLE PHASE MODULATION APPROACH TO AN INTERFEROMETRIC SYSTEM
(1992-09-15)
CHIEN, PY
;
PAN, RP
;
PAN, CL
;
交大名義發表
;
光電工程學系
A novel method for measuring the phase difference between interfering beams in an interferometric system is demonstrated by using a double phase modulation technique. There are two modulation signals applied to the interferometric system. The first modulation signal is used to modulate the path length for pseudo-heterodyne processing. The second modulation signal is used to modulate the frequency of the laser diode for equivalent wavelength synthesis. This approach is demonstrated by using a fiberoptic Mach-Zehnder interferometer.
FREE-SURFACE EFFECTS ON THE RESPONSE OF NEMATIC LIQUID-CRYSTAL FILMS TO A LASER-PULSE
(1993-05-01)
PAN, RP
;
CHEN, SM
;
YANG, HY
;
電子物理學系
;
光電工程學系
The dynamic response of 5CB films with a free surface to a laser pulse is investigated. A magnetic field above the Freedericksz transition is applied initially to induce a starting angle on the molecular orientation. A single 1.06 mum laser pulse with e-1 pulse width 0.2 ms is incident normally upon the films. When the laser pulse polarization is perpendicular to the magnetic field, only a thermal effect is involved. While it is parallel to the magnetic field, both molecular orientation and thermal effects are involved. The results from films with a free surface are compared with those from films sandwiched between two glass substrates. The free surface effect, beam size effect, and thermal effect are discussed by comparing with theoretical analysis.
IDENTIFICATION OF 3RD-ORDER AND 5TH-ORDER SELF-PHASE MODULATION EFFECTS IN LASER-INDUCED DIFFRACTION RINGS FROM A NEMATIC LIQUID-CRYSTAL FILM
(1990-11-15)
CHEN, SM
;
PAN, RP
;
PAN, CL
;
交大名義發表
;
光電工程學系
INTERFEROMETRIC MEASUREMENTS OF THE THICKNESS OF NEMATIC LIQUID-CRYSTAL FILMS WITH A FREE-SURFACE
(1989-12-01)
CHEN, SM
;
PAN, RP
;
PAN, CL
;
交大名義發表
;
電子物理學系
MAGNETIC-FIELD-INDUCED FREEDERICKSZ TRANSITION AND THE DYNAMIC-RESPONSE OF NEMATIC LIQUID-CRYSTAL FILMS WITH A FREE-SURFACE
(1991-03-15)
CHEN, SM
;
HSIEH, TC
;
PAN, RP
;
電子物理學系
;
光電工程研究所
The Freedericksz transition and the dynamic response of homeotropical liquid-crystal films with a free surface (FS) induced by a perpendicular dc magnetic field have been studied theoretically and experimentally for two nematic substances: 4'-n-pentyl-4-cyanobiphenyl (5CB) and 4'-n-octyl-4-cyanobiphenyl (8CB). For either one of these two materials, it is found that the critical magnetic field of these two nematic liquid-crystal (NLC) films with a free surface is equal to that of the NLC film with hard boundaries (HB) of the same thickness. This thus demonstrates a very strong orientational anchoring for 5CB and 8CB at the free surface. The intrinsic structures of FS samples are homeotropic, just as the HB ones are. For the dynamic response, the turn-off rates of FS samples are found to be about two times faster than those of the HB ones. This is interpreted with the backflow theory and the lack of positional anchoring on the free surface. Finally, a sensitive approach to determine the viscosity coefficients, gamma-1 and eta-c, of the NLC film is suggested.
OPTICAL 2ND-HARMONIC GENERATION FROM MAGNETIZED SURFACES
(1989-01-15)
PAN, RP
;
WEI, HD
;
SHEN, YR
;
電子物理學系
;
電子工程學系及電子研究所
OPTICAL 2ND-ORDER SUSCEPTIBILITY OF COPPER SURFACE DUE TO IMAGE POTENTIAL SURFACE-STATES
(1989-08-01)
WEI, HD
;
PAN, RP
;
YANG, TJW
;
電子物理學系
;
電控工程研究所
SELF-BENDING AND ASYMMETRIC SPATIAL SELF-PHASE MODULATION EFFECTS IN NEMATIC LIQUID-CRYSTAL FILMS
(1991-05-01)
PAN, RP
;
CHEN, SM
;
PAN, CL
;
電子物理學系
;
光電工程學系
Laser-induced beam bending and the far-field asymmetric diffraction ring pattern due to the self-bending and asymmetric spatial self-phase modulation (SPM) effects in nematic liquid-crystal films are investigated. The measured far-field patterns are in good agreement with numerical calculations based on the diffraction theory, taking into account the two dimensionally of the problem, the nonlocal effect, and the wave-front curvature effect. The individual contributions of the aforementioned effects to the far-field pattern are analyzed for the first time. It is shown that the outermost diffraction peak of the far-field pattern is not the strongest one and that a large fraction of the transmitted intensity remains in the central region (within +/- 6 mrad of the beam axis). Merging of some of the diffraction peaks in this region should also occur. Although the transmitted beam does deflect, the deflection angle does not increase monotonically with the incident laser intensity, as is the case for a purely Kerr-like medium. In the experiments discussed here, higher-order effects are present. As an example, it is shown that equally pronounced third- and fifth-order nonlinear optical SPM effects are responsible for an observed five-ring asymmetric ring pattern.
THE RESPONSE-TIME AND THE BACKFLOW EFFECT OF 5CB AND 8CB FILMS WITH A FREE-SURFACE IN MAGNETIC-FIELDS
(1991)
PAN, RP
;
CHEN, SM
;
HSIEH, TC
;
電子物理學系
;
光電工程學系