High reflection dielectric distributed Bragg reflector (DBR) can be used with high Q optical cavity to narrow down the spectrum optical source, for experimental quantum electro-dynamics, etc. To construct a free space optical cavity for a local oscillator of the state-of-the-art optical frequency standards, concave mirrors are used as one of the end mirrors of the cavity. Usually, the high reflection DBR is fabricated by depositing dielectric materials on a glass substrate. However, the ultimate stability of the optical cavity is limited by the thermal noise of dielectric DBR. To overcome this problem, a crystalline DBR was proposed to stabilize the optical cavity, which can reduce thermal noise. In this study, we fabricated crystalline DBR by GaAs/AlAs compound semiconductor on a concave GaAs substrate. Although a traditional semiconductor substrate has atomically flat surface, we fabricated a concave surface with a curvature radius of 1000 mm on the GaAs substrate by optical quality polishing. Then, we carried out wet etching and introduced it in vacuum chamber for molecular beam epitaxy (MBE). In the MBE growth chamber, we carried out thermal cleaning with As4 at a substrate temperature of 600°C. Next, the GaAs/AlAs DBR structure was grown at 580°C. The evaluation of surface roughness was conducted by atomic force microscopy, which showed a roughness of 0.165 nm in 1 × 1 um measurement such that a very smooth surface can be obtained.
Proc. SPIE. 8132, Time and Frequency Metrology III
KEYWORDS: Vacuum ultraviolet, High harmonic generation, Near infrared, Femtosecond phenomena, Prisms, Ferroelectric materials, Mirrors, Time metrology, Frequency metrology, Current controlled current source
We generate a VUV frequency comb centered at 159 nm as the 5th harmonic of Ti:S femto-second pulses by a passive enhancement using an external cavity. Average power up to 1.5 uW is measured by a solar-blind phototube. Stable generation about 10 minutes is obtained by active locking of the Ti:S frequencies to the enhancement cavity. Frequency tunability of our Ti:S comb teeth is also verified, which enables us to continuously sweep its frequency with more than twice a free spectral range. Those features reported here are indispensable to precision spectroscopy of unexplored atomic transitions in the VUV region.
An 87Sr-based-optical lattice clock in NICT is compared to that of The University of Tokyo using a >50 km fiber
link. In this work, we have demonstrated for the first time that two distant Sr lattice clocks generate the same
frequency with systematic uncertainty of 0.31 Hz (7.3 × 10-16 fractionally) for the 429 THz clock frequency.
Various activities of atomic frequency standards studied in National Institute of Information and Communications
Technology (NICT) are briefly reviewed. After BIPM accepted the first cesium fountain clock in NICT as a reference to
determine International Atomic Time (TAI), efforts to further reduce the uncertainty of collision shifts are ongoing. A
second fountain clock using atomic molasses is being built to enable the operation with less atomic density. Single ion
clock using calcium has been pursued for several years in NICT. The absolute frequency measured in 2008 has CIPM to
adopt the Ca+ clock transition as a part of the list of radiation (LoR) to realize the meter. Sr lattice clock has started its
operation last year. The absolute frequency agreed well with those obtained in other institutes. Study of stable cavities to
stabilize clock lasers are also introduced.
Buffer gas induced collision shift for the 88Sr 1S0-3P1 transition is investigated by precision saturation spectroscopy of
thermal gas in a heat cell. The cell was filled with rare gases of helium, neon, argon, and xenon as buffer gases. Helium
showed the largest fractional shift coefficient of 1.6x10-9 Torr-1. The disagreement between our experiments and simple impact calculations indicates effective atom losses from zero-velocity class which contributes to saturated absorption
spectroscopy. The result could be useful to evaluate the background gas collision shift of Sr lattice clocks.
Keywords: collision, saturated absorption spectroscopy, lattice clock, optical clock, density shift
Proceedings Volume Editor (2)
This will count as one of your downloads.
You will have access to both the presentation and article (if available).