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Browsing by Author "Shy, JT"

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    A calcium vapor cell for atomic spectroscopy
    (2002-11-01)
    Huang, MS
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    Lu, MH
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    Shy, JT
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    物理研究所
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    光電工程學系
    A calcium vapor cell used in laser spectroscopy usually suffers from calcium coating on the cell windows. To solve the problem, we add two mirrors in the cell to reflect the laser beam, then the calcium will coat on these mirrors instead of on the windows. Calcium coating degrades the reflectivity of the mirrors at the beginning, but the mirrors become calcium mirrors after a certain period of coating and their reflectivity will not change by further calcium coating. Using this cell in a conventional saturated-absorption spectroscopy, the observed saturated-absorption peak at 657 nm is about 2.4% of the probe beam power and its linewidth is below 300 kHz. Therefore, a portable secondary calcium-wavelength standard at 657 nm having an accuracy better than 1x10(-11) is possible. In addition, our cell has a continuous working time longer than 3 d and it can be easily extended to 10 d. (C) 2002 American Institute of Physics.
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    Far-infrared resonance in split ping resonators
    (2004-02-01)
    Hsu, AC
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    Cheng, YK
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    Chen, KH
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    Chern, JL
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    Wu, SC
    We experimentally investigated the resonance effect of planar metallic split ring resonators (SRRs) in the far-infrared region (FIR) (similar to10.6 mum). Experimental results indicated that they exhibit resonance around 10.6 mum, implying negative permeability in the FIR region. Furthermore, the ratio of effective dimensions of the SRR cell and the wavelength of the incident beam was around I which suggested a wide scale independence. This size tolerance is useful in realizing the meta-materials with negative indices of refraction in the optical wavelength domain.
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    Frequency stabilization of an external cavity diode laser to molecular iodine at 657.483 nm
    (2006-05-01)
    Fang, HM
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    Wang, SC
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    Shy, JT
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    光電工程學系
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    Department of Photonics
    The saturation spectrum of the P(84) 5-5 transition of I-127(2) at 657.483 nm is obtained with the third-harmonic demodulation method using an external cavity diode laser. The laser frequency is modulated by modulating the diode current instead of modulating the cavity length with a piezoelectric transducer (PZT). Current modulation allows a modulation frequency that is higher than PZT modulation. The signal-to-noise ratio of 1000 is better than previous results presented in the literature. The laser is frequency stabilized to the hyperfine component o of the P(84) 5-5 transition with a frequency stability of better than 10 kHz (2.2 X 10(-11) relative stability). (c) 2006 Optical Society of America.
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    High sensitivity bulk electro-optic modulator field sensor for high voltage environments
    (2004-12-01)
    Huang, MS
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    Lu, MH
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    Shy, JT
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    光電工程學系
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    Department of Photonics
    An optical electric field sensor is an effective instrument for surveying the electric or magnetic field around a high voltage electrical system. A Mach-Zender interferometer type modulator is generally used in this kind of sensor. The sensor has good sensitivity to electric or magnetic fields, but an unexpected high field could easily destroy the modulator owing to its short electrode separation. A bulk modulator usually has long separation between the two electrodes, which can prevent modulator breakdown, but its sensitivity is usually worse than the Mach-Zender interferometer type sensor. To solve this problem, a Fabry-Perot cavity is used to improve the sensitivity of the bulk modulator type sensor. This work also discusses the optimization of the sensor sensitivity. When the sensor works on the point where a cavity resonance has maximal slope, the proposed sensor has approximately the same sensitivity for sensing a field as the Mach-Zender interferometer type sensor. (C) 2004 American Institute of Physics.
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    Measurement of hyperfine splitting of molecular iodine at 532 nm by double-passed acousto optic modulator frequency shifter
    (2006-04-01)
    Fang, HM
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    Wang, SC
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    Liu, LC
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    Cheng, WY
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    Wu, KY
    The hyperfine splitting of molecular iodine R(56) 32-0 transition at 532 nm is measured using a double-passed acousto optic modulator frequency shifting apparatus. Preliminary results, compared with the values recommended by the Consultative Committee for Length, show that the accuracy of our method is better than 20 kHz, which can be easily improved in the future.
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    Novel method to stabilize a laser wavelength unaffected by Fabry-Perot etalon angle drift
    (2004-05-01)
    Huang, MS
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    Lu, MH
    ;
    Shy, JT
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    光電工程學系
    ;
    Department of Photonics
    A laser with its wavelength stabilized to a Fabry-Perot etalon has many industrial applications. An ideal error signal for laser stabilization is the dispersion-like signal generated without wavelength modulation. We present a technique, by which the error signal is generated by the difference of two resonance peaks of a Fabry-Perot etalon. A laser beam is split into two beams, which pass through an etalon with a small optical path length difference to generate two partially overlapped resonance peaks. Subtracting one peak from the other yields a dispersion-like error signal. The zero crossing of the differential signal is insensitive to the angle drift of the etalon if the incident angles of the two laser beams are nearly equal but with opposite sign. (C) 2004 Society of Photo-Optical Instrumentation Engineers.
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    Pressure and power broadening of the a(10) component of R(56) 32-0 transition of molecular iodine at 532 mn
    (2006-01-01)
    Fang, HM
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    Wang, SC
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    Shy, JT
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    光電工程學系
    ;
    Department of Photonics
    We determine the linewidth of the hyperfine structure a(10) component of R(56) 32-0 transition of I-127(2) at 532 nm using the dependence of the peak amplitude of the third-derivative signal on the modulation width. We also use the same method to investigate pressure broadening and power broadening of the a(10) component. (c) 2005 Elsevier B.V. All rights reserved.
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    Pulsed optical parametric generation, amplification, and oscillation in monolithic periodically poled lithium niobate crystals
    (2004-06-01)
    Chiang, AC
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    Wang, TD
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    Lin, YY
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    Lau, CW
    ;
    Chen, YH
    We conducted a series of passively Q-switched Nd:YAG laser pumped optical parametric generation, amplification, and oscillation experiments in monolithic periodically poled lithium niobate (PPLN) crystals. Double-pass optical parametric generation with an effective gain length of 10 cm in a PPLN crystal was performed in comparison with single-pass operation in the same crystal. By seeding a PPLN, optical parametric amplifier with a distributed feedback (DFB) diode laser, we produced 200-ps transform-limited laser pulses at 1549.6 mn and observed parametric gain competition at different pump levels. For optical parametric oscillations, we first demonstrated 22% power efficiency from a 2.4-cm intrinsic-cavity PPLN optical parametric oscillator pumped by a 4.2-ns, 10-kW passively Q-switched Nd:YAG laser. Preliminary studies on DFB optical parametric oscillators in PPLN are mentioned. The temporal and spectral properties of these optical parametric generators, amplifiers, and oscillators are characterized and discussed.
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    Simultaneous amplitude modulation and wavelength conversion in an asymmetric-duty-cycle periodically poled lithium niobate
    (2003-08-01)
    Chen, YH
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    Fan, FC
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    Lin, YY
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    Huang, YC
    ;
    Shy, JT
    We report the theory and experiment for an amplitude modulator and wavelength converter based on an electrode-coated asymmetric-duty-cycle periodically poled lithium niobate (PPLN). In a 56%/44% domain-duty-cycle PPLN crystal, we modulated the amplitude of the 532-nm second-harmonic output and measured a normalized half-wave voltage of 1.1 V x d (mum)/I-eff (cm), where d is the separation of the electrodes and I-cff is the effective electrode length defined by the PPLN length multiplying the deviation of the domain-duty-cycle from the 50% value. A modulation depth of 85% was obtained in the linear modulation regime. We also derived a unified theory to describe the half-wave voltage for two types of PPLN-based amplitude modulators. (C) 2003 Elsevier Science B.V. All rights reserved.
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    Triplet exciton formation and decay in polyfluorene light-emitting diodes
    (2005-09-01)
    Liao, HH
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    Meng, HF
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    Horng, SF
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    Shy, JT
    ;
    Chen, K
    We study the triplet excitons in poly (9,9-dioctylfluorene-2,7-diyl) light-emitting diode using infrared induced absorption. The infrared absorption is exclusively due to the triplet excitons and there is no spectral overlap with any other species. A strong suppression of the triplet exciton density relative to the singlet by voltage is observed. Through an unique independent measurement on the triplet exciton lifetime it is shown that the suppression solely comes from triplet exciton quenching by current injection. The triplet-to-singlet exciton formation ratio is independent of voltage as well as temperature, implying a spin-independent exciton formation.
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    Triplet exciton formation ratio in poly(p-phenylene-vinylene) light-emitting diode
    (2003-04-04)
    Lin, LC
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    Meng, HF
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    Shy, JT
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    Horng, SF
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    Yu, LS
    The triplet to singlet exciton formation ratio in a poly(2-methoxy-5(2'-ethyl-hexyloxy)-1,4-phenylene vinylene) (MEH-PPV) light-emitting-diode is measured by comparing the triplet induced-absorptions with optical and electric excitations at same singlet exciton density. The ratio is a strong universal decreasing function of the averaged electric field. Using 4 ns for singlet to triplet intersystem crossing time, the ratio is significantly larger than the spin-statistics value 3 at intermediate field but is reduced to about 1 for higher field.
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    Triplet-to-singlet exciton formation in poly(p-phenylene-vinylene) light-emitting diodes
    (2003-01-24)
    Lin, LC
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    Meng, HF
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    Shy, JT
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    Horng, SF
    ;
    Yu, LS
    The triplet to singlet exciton formation ratio in a MEH-PPV light-emitting diode is measured by comparing the triplet-induced absorptions with optical and electric excitations at the same singlet exciton density. The ratio is a strong universal decreasing function of the averaged electric field. Using 4 ns for singlet to triplet intersystem crossing time, the ratio is significantly larger than the spin-independent value 3 at intermediate field but is reduced to about 2 for higher field.