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Nakmura T.,University of Tokyo | Tani S.,University of Tokyo | Ito I.,University of Tokyo | Ito I.,Exploratory Research for Advanced Technology ERATO | And 2 more authors.
2016 Conference on Lasers and Electro-Optics, CLEO 2016 | Year: 2016

We propose a novel magneto-optic approach for high-bandwidth phase stabilization of the cavity length of fiber-based frequency combs. Stabilizing the mode-locked laser to an optical reference resulted in sub-hundred mrad residual phase noise. © 2016 OSA.


Ota S.,University of Tokyo | Kitagawa H.,University of Tokyo | Takeuchi S.,University of Tokyo | Takeuchi S.,Exploratory Research for Advanced Technology ERATO | Takeuchi S.,Japan Science and Technology Agency
Analytical Chemistry | Year: 2012

We present a simple microfluidic method to generate high-density femotoliter-sized microreactor arrays within microfluidic channels. In general, we designed a main channel with many small chambers built into its walls. After sequentially infusing aqueous solution and organic solvent from a single tube into the device, aqueous droplets are confined in the chambers by the solvent flow. The generated reactors are small and stable enough for carrying out ultrasensitive biochemical assays at single molecule levels. As a demonstration, in this paper, we optically observed hydrolysis activity of β-galactosidase enzymatic molecules in the reactor arrays at single molecule levels. Further, this method has the following advantages: (1) the droplets are observable immediately after formation and (2) its simple procedure is sufficiently robust such that even handy infusion of the preloaded solutions is reproducible. We believe our method provides a platform attractive to a variety of single molecule studies and sensing applications such as clinical diagnostics. © 2012 American Chemical Society.


Kuse N.,University of Tokyo | Kuse N.,Japan Science and Technology Agency | Kuse N.,Exploratory Research for advanced Technology ERATO | Ozawa A.,University of Tokyo | And 5 more authors.
Optics Express | Year: 2013

We demonstrate a fiber Bragg grating (FBG) strain sensor with optical frequency combs. To precisely characterize the optical response of the FBG when strain is applied, dual-comb spectroscopy is used. Highly sensitive dual-comb spectroscopy of the FBG enabled strain measurements with a resolution of 34 nε. The optical spectral bandwidth of the measurement exceeds 1 THz. Compared with conventional FBG strain sensor using a continuous-wave laser that requires rather slow frequency scanning with a limited range, the dynamic range and multiplexing capability are significantly improved by using broadband dual-comb spectroscopy. © 2013 Optical Society of America.


Kuse N.,University of Tokyo | Kuse N.,Japan Science and Technology Agency | Kuse N.,Exploratory Research for Advanced Technology ERATO | Ozawa A.,University of Tokyo | And 5 more authors.
Applied Physics Express | Year: 2012

We demonstrate dual-comb spectroscopy with relatively phase-locked two frequency combs, instead of frequency combs firmly fixed to the absolute frequency references. By stabilizing two beat frequencies between two mode-locked lasers at different wavelengths observed via freerunning continuous-wave (CW) lasers, two combs are tightly phase locked to each other. The frequency noise of the CW lasers barely affects the performance of dual-comb spectroscopy because of the extremely fast common-mode noise rejection. Transform-limited comb-resolved dualcomb spectroscopy with a 6 Hz radio frequency linewidth is demonstrated by the use of Yb-fiber oscillators. © 2012 The Japan Society of Applied Physics.


Nishimura K.,Osaka University | Toyota T.,University of Tokyo | Suzuki H.,Osaka University | Suzuki H.,Exploratory Research for Advanced Technology ERATO | And 2 more authors.
14th International Conference on Miniaturized Systems for Chemistry and Life Sciences 2010, MicroTAS 2010 | Year: 2010

We present a method to control the size of giant unilamellar vesicles (GUVs), in which biochemical reaction can be encapsulated and conducted, with the aid of microfluidics. GUVs were formed by passing the water-in-oil (W/O) emulsion droplets through the second oil/water interface by centrifugation. Last year we showed that, by controlling the size of the initial W/O emulsion with a flow-focusing device, size of the lipid vesicles can also be controlled. Here we examined the physical condition that determines the vesicle size, and showed that our method is compatible with biochemical reactions for artificial cell-model studies.


Endo M.,University of Tokyo | Endo M.,Exploratory Research for Advanced Technology ERATO | Ito I.,University of Tokyo | Ito I.,Exploratory Research for Advanced Technology ERATO | And 2 more authors.
Optics Express | Year: 2015

A 15-GHz mode spacing optical frequency comb based on a Kerr-lens mode-locked Yb:Y2O3 ceramic laser has been developed. Individual modes were clearly resolved by a commercial spectrometer. To demonstrate the long-term operation of the optical frequency comb, a single longitudinal mode was phase-locked to a frequency-stabilized continuous wave laser and the repetition rate to a radio frequency standard. To the best of our knowledge, 15 GHz is the largest reported mode spacing (repetition rate) for both a Kerr-lens mode-locked laser and a direct femtosecond laser based-optical frequency comb. © 2015 Optical Society of America.


Endo M.,University of Tokyo | Endo M.,Exploratory Research for Advanced Technology ERATO | Ozawa A.,University of Tokyo | Ozawa A.,Exploratory Research for Advanced Technology ERATO | And 2 more authors.
Optics Letters | Year: 2013

A laser diode (LD)-pumped, 6-GHz repetition rate, ytterbium (Yb)-doped Lu2O3 ceramic Kerr-lens mode-locked laser is described. A bow-tie ring cavity enabled the generation of femtosecond pulses centered at a wavelength of 1076 nm with an average power of 10 mW. The pulse duration after an amplifier was 161 fs whereas the transform-limited pulse duration directly from the oscillator was 148 fs. The repetition frequency was sufficiently high for each longitudinal mode to be spectrally resolved by a commercially available optical spectrum analyzer. The developed laser was successfully applied to the absorption spectroscopy of metastable 4helium and demonstrated the suitability of the system as a source for comb-resolved broadband spectroscopy. © 2013 Optical Society of America.


Nakamura T.,University of Tokyo | Ito I.,University of Tokyo | Ito I.,Exploratory Research for Advanced Technology ERATO | Kobayashi Y.,University of Tokyo | Kobayashi Y.,Exploratory Research for Advanced Technology ERATO
Optics Express | Year: 2015

We demonstrate a passively offset-frequency stabilized optical frequency comb centered at 1060 nm. The offset-free comb was achieved through difference frequency generation (DFG) between two portions of a supercontinuum based on a Yb:fiber laser. As the DFG comb had only one degree of freedom, repetition frequency, full stabilization was achieved via locking one of the modes to an ultrastable continuous wave (CW) laser. The DFG comb provided sufficient average power to enable further amplification, using Yb-doped fiber amplifier, and spectral broadening. The spectrum spanned from 690 nm to 1300 nm and the average power was of several hundred mW, which could be ideal for the comparison of optical clocks, such as optical lattice clocks operated with Sr (698 nm) and Hg (1063 nm) reference atoms. © 2015 Optical Society of America.


Guerin L.,Exploratory Research for Advanced Technology ERATO | Guerin L.,High Energy Accelerator Research Organization | Hebert J.,Rennes Institute of Physics | Buron-Le Cointe M.,Exploratory Research for Advanced Technology ERATO | And 8 more authors.
Physical Review Letters | Year: 2010

Achieving control of photoinduced phase transitions requires understanding how materials work during transformation induced by a laser pulse. Here we investigate the precursors of a photoinduced phase transition in the highly cooperative charge-transfer molecular crystal tetrathiafulvalene-p-chloranil and provide key insights. The photogeneration of one-dimensional nanoscale clusters was detected by time-resolved diffuse x-ray scattering with 50-ps time resolution. Such clustering of structurally relaxed electronic excitations is expected to be a common process in many materials presenting photoinduced transformations.© 2010 The American Physical Society.


Endo M.,University of Tokyo | Endo M.,Exploratory Research for Advanced Technology ERATO | Ozawa A.,University of Tokyo | Ozawa A.,Exploratory Research for Advanced Technology ERATO | And 2 more authors.
Optics Express | Year: 2012

We developed a laser-diode pumped, 4.6-GHz repetition-rate, Yb:KYW Kerr-lens mode-locked femtosecond oscillator. A bow-tie ring cavity generates an output power of 14.6 mW with a spectrum width of 11 nm at 1046 nm. To the best of our knowledge, this is the highest-repetition frequency in the laser-diode pumped femtosecond Kerr-lens mode-locked laser. © 2012 Optical Society of America.

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