Details of a Researcher - Hasegawa, Taro

Papers - Hasegawa, Taro

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Twisted radio frequency ion traps for all-metal string ion traps

Taro Hasegawa

Review of Scientific Instruments (American Institute of Physics) 96 ( 10 ) 103201-1 - 103201-7 2025.10

Research paper (scientific journal), Single Work, Lead author, Last author, Corresponding author, Accepted

Twisted radio frequency (rf) ion traps, which have electrode configurations that are twisted variants of conventional linear rf ion traps, have been proposed and successfully demonstrated using charged alumina dust particles. When constructed from thin metal wire electrodes, the twisted traps offer excellent optical accessibility to the trapped ions, making them suitable for applications in quantum information technology. In the experimental demonstration, 14 μm-diameter alumina dust particles were charged via discharge and successfully confined in the twisted trap. A linear chain of trapped particles was observed within the trap.

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Improvement in the Sagnac-loop laser frequency stabilization

Taro Hasegawa

Journal of Optical Society of America B (Optica) 42 ( 2 ) 285 - 291 2025.01

Research paper (scientific journal), Single Work, Lead author, Last author, Corresponding author, Accepted

The laser frequency stability locked to the D2 transition of 85Rb at 780 nm using a Doppler-free Sagnac-loop stabilization scheme has been improved. In a previous work [J. Opt. Soc. Am. B 40, 667 (2023)], changes in birefringence at the absorption cell windows, influenced by the cell temperature, and in the rubidium vapor, affected by magnetic field fluctuations, significantly influenced the laser frequency stability. By aligning the polarization, the short-term stability (<10 s) of the locked laser frequency was improved; however, the long-term stability remained unaffected. We attribute this long-term stability to temperature-induced changes in the optical path length of the wave plates. By removing the wave plates from the setup, the long-termstability has been successfully improved.

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Phase structure of harmonically mode-locked optical frequency combs

Taro Hasegawa

Optics Express (Optica) 32 ( 5 ) 8092 - 8100 2024.02

Research paper (scientific journal), Single Work, Lead author, Last author, Corresponding author, Accepted

Carrier phase of a harmonically mode-locked optical frequency comb (OFC) is investigated in detail. While harmonically mode-locked OFCs show promise for high-repetition-rate applications, their mode spacing is not the same as the pulse repetition rate, unlike fundamentally mode-locked OFCs. Consequently, harmonically mode-locked OFCs are unsuitable for applications requiring OFCs with wide mode spacing. This study examines the pulse-to-pulse carrier phase evolution of 4th- and 5th-order harmonically mode-locked OFCs, revealing uneven carrier phase evolution responsible for the narrow mode spacing. The possibility of achieving harmonically mode-locked OFCs with wide mode spacing is suggested by implementing pulse-to-pulse phase modulation to ensure even phase evolution.

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Evaluation of the Sagnac-loop laser frequency stabilization to sub-Doppler spectral lines

Taro Hasegawa

Journal of Optical Society of America B (Optica) 40 ( 3 ) 667 - 672 2023.03

Research paper (scientific journal), Single Work, Lead author, Last author, Corresponding author, Accepted, ISSN 07403224

Laser frequency stability locked to D2 transition of 85Rb at 780 nm by the Sagnac-loop stabilization scheme was evaluated using the heterodyne measurement with an optical frequency comb. This scheme does not require modulation and magnetic field to generate the feedback error signal. Therefore, the setup for the laser frequency stabilization is simple. Because of the mechanical stability of the Sagnac interferometer, the dispersion of atom transition, which is used as an error signal for feedback loop, can be observed with negligibly small effects of mechanical fluctuations. In the experiment, the Allan variance for relative frequency uncertainty was 2.6×10-12 over 64 s averaging.

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Mode spacing multiplication of optical frequency combs without power loss

Taiki Kageyama, Taro Hasegawa

Optics Express (Optica) 30 ( 11 ) 19090 - 19099 2022.05

Research paper (scientific journal), Joint Work, Last author, Corresponding author, Accepted

We demonstrate the mode spacing multiplication of optical frequency combs (OFCs) using interleaving technique. The pulse train of an OFC after interleaving is phase modulated, and phase demodulation is necessary for mode spacing multiplication. This scheme enables mode spacing multiplication without power loss in principle, which is in contrast to the conventional mode filtering technique. During demonstration, the mode spacing of the OFC of a mode-locked Er-doped fiber laser (repetition rate of 97 MHz) is quadrupled by the interleaving process and successive phase demodulation.

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Fast polarization control for optical frequency combs

Taiki Kageyama, Taro Hasegawa

Optics Express (Optica) 29 ( 23 ) 38477 - 38487 2021.11

Research paper (scientific journal), Joint Work, Last author, Corresponding author, Accepted

Polarization of an optical frequency comb is electrically controlled using a waveguide electro-optic phase modulator (WG-EOM). Owing to the low operation voltage and wide electric bandwidth of the WG-EOM, fast polarization control is possible. It is found that birefringence of the WG-EOM and polarization-maintaining optical fibers causes polarization-dependent pulse separation, which makes polarization control of the optical frequency comb impossible. Therefore, compensation of the birefringence is required for polarization control. In the experiment, a delay line in free space is used for birefringence compensation, and pulse-to-pulse polarization control of an optical frequency comb (with a repetition rate of 100 MHz) is demonstrated.

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260 kHz mode-spacing optical frequency combs for scan-free high-resolution direct-comb spectroscopy

Taro Hasegawa

Optics Express (The Optical Society) 28 ( 22 ) 32837 - 32846 2020.10

Research paper (scientific journal), Single Work, Lead author, Last author, Corresponding author, Accepted

For scan-free high-resolution direct-comb spectroscopy, mode spacing of an optical
frequency comb is reduced down to 260 kHz by phase modulation. It turns out that timedomain signal is degraded by averaging because of slow optical path length fluctuations and
fast optical pulse timing jitter. In this study, compensation of these effects is introduced, and
signal degradation by averaging is avoided. With demonstrations of direct-comb spectroscopy
with the narrow-mode-spacing optical frequency comb, Doppler-limited absorption spectrum of
methane and reflection spectrum from an optical ring cavity are observed. As a result, detailed
resonance spectral line profile of 8 MHz linewidth for the optical ring cavity is obtained in 50 ms
measurement time.

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Robust offset locking of laser frequency with electronically tunable LC circuits for sub-millihertz uncertainty

Yuhei Seishu, Taro Hasegawa

Applied Physics B (Springer) 125 ( 8 ) 142(1) - 142(8) 2019.07

Research paper (scientific journal), Joint Work, Last author, Corresponding author, Accepted

A simple scheme for laser frequency offset locking introduced in Cheng et al. (Opt Express 25:2752, 2017) has been improved by the use of a variable-capacitance diode. By employing this scheme with the optical phase lock loop, robust and precise laser frequency stabilization is achieved, and long-term laser frequency drift is expected to be substantially suppressed even in noisy circumstances. The optical frequency uncertainty becomes less than 10 μ Hz for 1000 s averaging.

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Mode density multiplication of an optical frequency comb by N<sup>2</sup> with phase modulation

Hasegawa T.

Optics Express (The Optical Society) 26 ( 19 ) 24551 - 24563 2018.09

Research paper (scientific journal), Single Work, Lead author, Last author, Corresponding author, Accepted

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A radio-frequency ion trap with string electrodes

Daisuke Kanai, Taro Hasegawa

Review of Scientific Instruments (American Institute of Physics) 89 ( 2 ) 023106-1 - 023106-5 2018.02

Research paper (scientific journal), Joint Work, Last author, Corresponding author, Accepted, ISSN 00346748

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Optical bistability induced by Gouy phase shift

Taro Hasegawa

Journal of Optical Society of America B (The Optical Society) 34 ( 7 ) 1319 - 1326 2017.07

Research paper (scientific journal), Single Work, Lead author, Last author, Corresponding author, Accepted

Optical bistability in a passive ring cavity with no designed nonlinear materials is experimentally observed in the near-infrared region. The nonlinear material that induces the optical bistability is considered to be water molecules in atmosphere. In the model calculation, it is found that the optical bistability is induced by transversal distribution of optical power-dependent refractive index of water in the Gaussian beam, which causes the power-dependent Gouy phase shift in the cavity. The model calculation agrees qualitatively with the experimental results. This result suggests that the Gouy phase shift has an effect on cavity-enhanced molecular spectroscopy.

Direct-comb molecular spectroscopy by heterodyne detection with continuous-wave laser for high sensitivity

Taro Hasegawa, Hiroyuki Sasada

Optics Express (The Optical Society) 25 ( 16 ) A680 - A688 2017.06

Research paper (scientific journal), Joint Work, Lead author, Corresponding author, Accepted

We have demonstrated direct-comb molecular spectroscopy in which an individualcomb mode is resolved by heterodyne detection with a continuous-wave (cw) laser. This simple, fast, and sensitive technique was demonstrated for atomic spectroscopy in [Appl. Phys. Lett. 101, 051105 (2012)], but is more suitable for molecular spectroscopy. Four rotation-vibration transitions of methane have simultaneously been recorded in a Doppler-limited resolution using a spectrally broadened comb based on an Er-doped fiber laser and a cw 1651-nm distributedfeedback laser diode. Even though the power level of the comb modes and the sample absorption are weaker than those of the previous studies, in this work the cw laser frequency is stabilized to one of the comb modes, and the data are thereby averaged for extended periods of time, resulting an improvement in sensitivity.

Broadened optical spectrum of repetitionrate-multiplied erbium-doped fiber comb

Taro Hasegawa

Journal of Optical Society of America B (The Optical Society) 33 ( 10 ) 2057 - 2061 2016.10

Research paper (scientific journal), Single Work, Lead author, Last author, Corresponding author, Accepted

The repetition rate of an erbium-doped fiber comb is multiplied by an optical cavity for filtering, and the optical spectral distribution is broadened in a highly nonlinear fiber. For erbium-doped fiber combs, filtering cavities are commonly used to obtain the high-repetition-rate combs by the repetition rate multiplication. After the multiplication, optical spectral broadening by a highly nonlinear fiber is necessary for applications to optical frequency measurements in broad bandwidth and astronomy. In this study, the broadened spectrum covers over the range from 1050 to 2250 nm, which is over an octave so that the determination of the filtered mode numbers is feasible. The optical power of the broadened beam within a narrow optical bandwidth is also measured in the time domain and in the frequency domain to examine the broadening property.

Nonlinear absorption and phase shift in coupled optical cavities

Taro Hasegawa

Physical Review A (American Physical Society) 92 ( 4 ) 043815-1 - 043815-5 2015.10

Research paper (scientific journal), Single Work, Lead author, Last author, Corresponding author, Accepted

The nonlinear absorption process and associated phase shift in coupled optical cavities are studied experimentally by observing optical resonance properties. In the coupled cavity configuration, two optical cavities, one for a fundamental beam and the other for a second-harmonic (SH) beam, are coupled by a nonlinear crystal for the second-harmonic generation (SHG). The cavity for the SH beam effectively extends the nonlinear crystal length so that the frequency-conversion efficiency of the SHG, which is proportional to the square of the crystal length, is enhanced. In the observation, power reduction of the fundamental beam at resonance is observed as a small dip in the resonance curve. According to a model calculation, it is found that this power reduction is caused by blue-induced infrared absorption.

Theoretical analysis of mid-infrared molecular spectral line profiles with transversal relaxation in an intense optical field

Taro Hasegawa

Journal of Optical Society of America B (The Optical Society) 31 ( 8 ) 1879 - 1884 2014.08

Research paper (scientific journal), Single Work, Lead author, Last author, Corresponding author, Accepted

Nonlinear effects by intense optical field on mid-infrared spectral lines (∼3 μm) are discussed. Recent development of intense mid-infrared coherent radiation makes nonlinear mid-infrared spectroscopy possible. In the midinfrared region, the transversal relaxation process is important compared to the visible or near-infrared region. In the analysis, a two-energy-state system is discussed. The intense pump beam scattering spectral lines (Mollow triplet) and the absorption spectral lines of the probe beam with the intense pump beam are calculated.

Stabilization of the coupled resonant cavity without dither

Taro Hasegawa

Optics Communications (Elsevier) 308 270 - 273 2013.11

Research paper (scientific journal), Single Work, Lead author, Last author, Corresponding author, Accepted

A simple scheme without dither to obtain an error signal for the stabilization of the coupled-cavity configuration for efficient fourth harmonic generation of continuous-wave lasers is proposed and demonstrated. This scheme is ananalogue of the noise immune cavity enhanced optical heterodyne molecular spectroscopy (NICEOHMS) technique. In the proposed scheme, the robust stabilization is expected in comparison with the dither lock technique. In the demonstration, the stabilization of the coupled resonant cavity at the resonance is successfully achieved without the noise caused by the dither.

Fourth harmonic generation of continuous-wave lasers in coupled-cavity configuration

Taro Hasegawa

Optics Communications (Elsevier) 285 ( 24 ) 5368 - 5371 2012.11

Research paper (scientific journal), Single Work, Lead author, Last author, Corresponding author, Accepted

Frequency quadrupling of a continuous-wave laser is carried out in coupled cavities with the stabilization to the resonance. The fourth harmonic generation in the coupled cavities is expected to be more efficient than in the two build-up cavity configuration in tandem, because input couplers, which increase the optical loss of the cavity, are not required. The cavity length is stabilized by the feedback of the error signal obtained by the cavity length modulation. In the present demonstration, the ultraviolet beam of 6 mW at 238 nm is obtained by the fourth harmonic generation of the near infrared laser of 180 mW at 952 nm. This output power is expected to become higher (~ 1.7 mW) when the cavity setup is optimized.

Modulation-free laser frequency stabilization to a saturated sub-Doppler spectral line in a transversal magnetic field

Sho Okubo, Kana Iwakuni, Taro Hasegawa

Optics Communications (Elsevier) 285 ( 20 ) 4107 - 4111 2012.09

Research paper (scientific journal), Joint Work, Last author, Corresponding author, Accepted

We demonstrate frequency stabilization of a modulation-free laser to a saturated absorption spectral line of atoms in a transversal magnetic field. This stabilization scheme has been proposed for wide capture range in comparison with the dichroic atomic vapor laser lock (DAVLL) scheme and demonstrated for a Doppler-broadened spectral line in J. Opt. Soc. Am. B, 26, 1216 (2009). In this paper, a 1083-nm external-cavity laser diode is frequency-stabilized to the sub-Doppler spectral line of helium transition (2^3 S_1, m_J = 0 <-> 2 ^3P_0). Even though the error signal shape strongly depends on the pump beam polarization, the stabilized frequency is expected to be insensitive to the pump beam polarization.

Efficient photo-ionization for barium ion trapping using a dipole-allowed resonant two-photon transition

Guenther. Leschhorn, Taro Hasegawa, Tobias Schaetz

Applied Physics B (Springer) 108 ( 1 ) 159 - 165 2012.07

Research paper (scientific journal), Joint Work, Accepted

Two efficient and isotope-selective resonant twophoton ionization techniques for loading barium ions into radio-frequency (RF)-traps are demonstrated. The scheme of using the strong dipole-allowed transition 6s2 1S0 → 6s6p 1P1 at λ = 553 nm as a first step towards ionization is compared to the established technique of using a weak inter-combination line (6s2 1S0 →5d6p 3D1,λ = 413 nm). An increase of two orders of magnitude in the ionization efficiency is found favoring the transition at 553 nm. This technique can be implemented using commercial all-solidstate laser systems and is expected to be advantageous compared to other narrowband photo-ionization schemes of barium in cases where highest efficiency and isotope-selectivity are required.

Sympathetic cooling of a mass-mismatched two-ion chain in a double-well trap potential

HASEGAWA TARO

Physical Review A (American Physical Society) 83 ( 5 ) 053407-1 - 053407-6 2011.05

Research paper (scientific journal), Single Work, Lead author, Last author, Corresponding author, Accepted

Sympathetic cooling of two-ion system, in which one is laser-cooled and the other is sympathetically cooled and their masses are mismatched, in a linear rf trap with a double-well potential is proposed. The double-well potential consists of two wells, and there is one ion in each well. The axial frequencies of the two wells and the spatial interval between them are experimentally controllable. By theoretical analysis, the normal modes of the small oscillations around the equilibrium are derived, and a measure of the sympathetic cooling rate is obtained. As a result, it is found that the sympathetic cooling rate is fast when the frequency of the axial motion of the sympathetically cooled ion is close to that of the laser-cooled ion. In the double-well potential, the sympathetic cooling rate of the ion species whose mass is much heavier or lighter than that of the laser-cooled ion can be fast. The sympathetic cooling rate of C60 + by the laser-cooled Ba+ in the double-well potential is estimated to be about 80 times faster than in the conventional setup. The double-well potential may be made by the microfabricated electrode configuration or by the optical dipole force trap.

Quantum mechanics in rotating-radio-frequency traps and Penning traps with a quadrupole rotating field

Kazuya Abe, Taro Hasegawa

Physical Review A (American Physical Society) 81 ( 3 ) 033402-1 - 033402-7 2010.03

Research paper (scientific journal), Joint Work, Last author, Corresponding author, Accepted

Quantum-mechanical analysis of ion motion in a rotating-radio-frequency (rrf) trap or in a Penning trap with a quadrupole rotating field is carried out. Rrf traps were introduced by Hasegawa and Bollinger [Phys. Rev. A 72, 043404 (2005)]. The classical motion of a single ion in this trap is described by only trigonometric functions, whereas in the conventional linear radio-frequency (rf) traps it is by the Mathieu functions. Because of the simple classical motion in the rrf trap, it is expected that the quantum-mechanical analysis of the rrf traps is also simple compared to that of the linear rf traps. The analysis of Penning traps with a quadrupole rotating field is also possible in a way similar to the rrf traps. As a result, the Hamiltonian in these traps is the same as the two-dimensional harmonic oscillator, and energy levels and wave functions are derived as exact results. In these traps, it is found that one of the vibrational modes in the rotating frame can have negative energy levels, which means that the zero-quantum-number state (“ground” state) is the highest energy state.

Laser frequency locking by dispersive response of atoms in transversal magnetic field

Taro Hasegawa, Mitsuyasu Deguchi

Journal of Optical Society of America B (The Optical Society) 26 ( 6 ) 1216 - 1220 2009.06

Research paper (scientific journal), Joint Work, Lead author, Corresponding author, Accepted

A robust laser-frequency-locking scheme to atomic transitions is proposed and demonstrated. In this scheme, dispersion of the Zeeman-shifted atoms instead of absorption in the dichroic atomic vapor laser lock (DAVLL) [Appl. Opt. 37, 3295 (1998)] is measured and used as an error signal for stabilization feedback. The error signal of the proposed scheme can provide a wide locking range. Experimental demonstration with the transition between 5d 2D3/2 and 6p 2P1/2 of Ba+ is carried out for a grating feedback external-cavity laser diode at 650 nm.

Rotating-radio-frequency ion traps

Taro Hasegawa, John J. Bollinger

Physical Review A (American Physical Society) 72 ( 4 ) 043403-1 - 043403-8 2005.10

Research paper (scientific journal), Joint Work, Lead author, Accepted

We discuss a radio-frequency (rf) ion trap, the rotating-radio-frequency (rotating-rf) trap, in which the motion of a charged particle is described by trigonometric functions rather than the usual Mathieu functions of a normal rf trap. In the rotating-rf trap, a rotating quadrupole electric field confines charged particles, whereas in a normal rf trap, an oscillating quadrupole electric field does. Ion motion in a rotating-rf trap is a superposition of two nondegenerate circular secular motions and two corresponding circular micromotions. The cases of applying a uniform dc magnetic field or a quadrupole dc electric field in addition to the rotating-rf field are also discussed. Confinement in a rotating-rf trap can be tighter than in a normal linear rf trap with the same experimental parameter values.

Stability of a Penning trap with a quadrupole rotating electric field

Taro Hasegawa, Marie J. Jensen, John J. Bollinger

Physical Review A (American Physical Society) 71 ( 2 ) 023406-1 - 023406-6 2005.02

Research paper (scientific journal), Joint Work, Accepted

We present theoretical and experimental studies of the center-of-mass (c.m.) stability of ions in a Penning trap with a quadrupole rotating electric field. The rotation frequency of an ion cloud in a Penning trap determines the cloud density and shape, and it can be precisely controlled by a rotating electric field. The quadrupole rotating-field scheme can control pure single-species plasmas in contrast to the dipole field, which is effective only for plasmas composed of two or more species of ions. However, the quadrupole field can modify the trap stability because of the spatial dependence of the electric field. In this study, we theoretically and experimentally determine the c.m. stability condition for ions in a Penning trap with a rotating quadrupole field. The experimental results agree well with the theoretical prediction. In the limit of zero magnetic field we obtain a type of rf trap which uses a rotating quadrupole field and in which the c.m. motion is analytically solvable.

Rapid Heating of a Strongly Coupled Plasma near the Solid-Liquid Phase Transition

Marie J. Jensen, Taro Hasegawa, John J. Bollinger, Daniel H. E. Dubin

Physical Review Letters (American Physical Society) 95 ( 2 ) 025001-1 - 025001-4 2005.01

Research paper (scientific journal), Joint Work, Accepted

Between 104 and 106 9Be+ ions were trapped in a Penning trap and laser cooled to ~1 mK, where they formed a crystalline plasma. We measured the ion temperature as a function of time after turning off the laser cooling and observed a rapid temperature increase as the plasma underwent the solid-liquid phase transition at T ’~ 10 mK ( Γ ~ 170). We present evidence that this rapid heating is due to a sudden release of energy from weakly cooled degrees of freedom involving the cyclotron motion of trapped impurity ions. This equilibration of cyclotron motion with motion parallel to the magnetic field is more than 10 orders of magnitude faster than that predicted by currently available theory, which is valid only in the absence of correlations (Γ<< 1).

Temperature and heating rate of ion crystals in Penning traps

Marie J. Jensen, Taro Hasegawa, John J. Bollinger

Physical Review A (American Physical Society) 70 ( 3 ) 033401-1 - 033401-13 2004.09

Research paper (scientific journal), Joint Work, Accepted

We have determined the temperature and heating rate of laser-cooled ions in a Penning trap using Doppler laser spectroscopy. Between 104 and 106 9Be+ ions are trapped in a Penning trap and Doppler laser cooled to temperatures of a few millikelvin, where they form ion crystals. This system is an example of a strongly coupled one-component plasma. The ion temperature was measured as a function of time after turning off the laser-cooling. In the solid phase, we measured a heating rate of ~65 mK/ s. Information about possible heating mechanisms was obtained directly from temperature measurements, and also from measurements of the rate of radial expansion of the ion plasma. We determined that the observed heating is due to collisions with the ~4x 10−9 Pa residual gas of our vacuum system.

Limiting temperature of sympathetically cooled ions in a radio-frequency trap

Taro Hasegawa, Tadao Shimizu

Physical Review A (American Physical Society) 67 ( 1 ) 013408-1 - 013408-4 2003.01

Research paper (scientific journal), Joint Work, Lead author, Accepted

Resonant oscillation modes of sympathetically cooled ions in a radio-frequency trap

Taro Hasegawa, Tadao Shimizu

Physical Review A (American Physical Society) 66 ( 6 ) 063404-1 - 063404-5 2002.12

Research paper (scientific journal), Joint Work, Lead author, Accepted

Sympathetic cooling of Ca+, Zn+, Sr+, Ba+, and Yb+ as guest ions with laser-cooled 24Mg+ as host ions in a rf ion trap is carried out, and resonant frequencies of their motion in the trap potential are measured. Various oscillation modes of the sympathetically cooled ions are observed. The resonant frequency of the oscillation mode is different from the frequency of either the collective oscillation frequency of the trapped ions or the oscillation frequency of each ion without host ions. This difference is well explained by a theoretical model in which coupled equations of motion of the host ion cloud with a single guest ion are considered.

Spin dynamics of dense alkali-metal atoms

Kiyoshi Ishikawa, Togo Kojima, Taro Hasegawa, Yoshihiro Takagi

Physical Review A (American Physical Society) 65 ( 3 ) 032511-1 - 032511-9 2002.02

Research paper (scientific journal), Joint Work, Accepted

The free induction signals of dense Rb atoms are observed with an injection-seeded power laser diode. The decay rate of signals is found to depend on the number density of Rb atoms, the static magnetic field, the electron spin polarization, and the pulse area of the oscillating magnetic field. We note that the observed broadening of the magnetic resonance line, appearing at high polarization and large pulse area, is the key to understanding the spin dynamics of the precessing atoms which interact with each other. The feature of broadening is quantitatively interpreted by numerically calculating, in a wide range of parameters, the nonlinear Liouville equation that includes the spin-exchange interaction between Rb atoms.

Observation and Temperature Measurement of Sympathetically Cooled Ions in an RF Trap

Taro Hasegawa, Tadao Shimizu

IEEE TRANSACTIONS ON INSTRUMENTATION AND MEASUREMENT (IEEE) 50 ( 2 ) 556 - 558 2001.04

Research paper (scientific journal), Joint Work, Lead author, Accepted

Removal of irrelevant isotope ions in the presence of laser cooling in a rf trap

Taro Hasegawa, Tadao Shimizu

Applied Physics B (Springer) 70 ( 6 ) 867 - 871 2000.06

Research paper (scientific journal), Joint Work, Lead author, Accepted

Charge transfer between a laser-cooled ion and a thermal atom in a radio-frequency trap

Taro Hasegawa, Tadao Shimizu

AIP Conference Proceedings (American Physical Society) 500 704 - 708 2000.02

Research paper (international conference proceedings), Joint Work, Lead author, Accepted

レーザー冷却・共同冷却されたrfトラップ中のイオンの運動

長谷川太郎

博士学位論文(東京大学) 1 - 119 2000.01

Doctoral thesis, Single Work, Lead author, Last author, Corresponding author, Accepted

Frequency-doubled Hermite-Gaussian beam and the mode conversion to the Laguerre-Gaussian beam

Taro Hasegawa, Tadao Shimizu

Optics Communications (Elsevier) 160 ( 1-3 ) 103 - 108 1999.02

Research paper (scientific journal), Joint Work, Lead author, Accepted

Distortion of spectral line profiles of laser-cooled ions in a radio-frequency ion trap

Taro Hasegawa, Daisuke Tanooka, Tadao Shimizu

Physical Review A (American Physical Society) 58 ( 3 ) 2327 - 2331 1998.09

Research paper (scientific journal), Joint Work, Lead author, Accepted

Nonlinear dynamics of two particles in the rf trap

Taro Hasegawa, Kiyoji Uehara

Progress in Crystal Growth and Characterization of Materials (Elsevier) 33 ( 1-3 ) 401 - 403 1996.01

Research paper (scientific journal), Joint Work, Lead author, Accepted

The dynamics of two particles in the rf trap is investigated theoretically. To solve tile nonlinear equations of motion nmnerieally, we introduce a new method based upon the Fourier expansion. Several new kinds of solutions including those that have a period two or four times the rf period are found and their stability diagrams in the parameter space are obtained. The results exhibit the bistability which may be related to the hysteresis observed in the phase transitions between the "crystal" state and the "cloud" state.

Dynamics of a single particle in a Paul trap in the presence of the damping force

Taro Hasegawa, Kiyoji Uehara

Applied Physics B (Springer) 61 159 - 163 1995.08

Research paper (scientific journal), Joint Work, Lead author, Accepted

The motion of a single charged particle in a Paul trap in the presence of the damping force is investigated theoretically and the modified stability diagrams in the parameter space are calculated. The results show that the stable regions in the a-q parameter plane are not only enlarged but also shifted. Consequently, the damping force causes instability in some cases, contrary to intuition. As a by-product of the calculation, we derive new theoretical approximate expressions for the secular-oscillation frequency. In the limiting case of no damping, these formulas are in good agreement with early measurements done by Wuerker et al.

Dynamics of two particles in an rf trap

Taro Hasegawa

修士学位論文(慶應義塾大学) 1 - 46 1995.03

Master’s thesis, Single Work, Lead author, Last author, Corresponding author, Accepted

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