Two strontium optical lattice clocks (Sr1 and Sr2) are being built at National Institute of Metrology(NIM) of China. Sr1 was firstly evaluated in 2015, and later equipped with a new clock laser based on a 30 cm reference cavity, which helped to improve its stability. Sr2 is built on a new campus of NIM, which has some different designs compared to Sr1, for example, a permanent magnets based Zeeman slower, a differential pumping stage, and a robust laser system. A time interleaved self-comparison campaign of Sr2 of more than 7 days shows an up-time of ~90% and a measurement stability of 3.7×10-15/√𝜏 with a 10 cm ULE cavity based clock laser. The link between these two optical clocks, that consists of two fiber optical frequency combs and a 54 km fiber connection, are being constructed. The comparison of these two clocks is planned in the near future.
A theoretical model is analyzed to evaluate the laser emission efficiency and the ratio of heat generation in the gain medium which are calculated by the output optical laser power vs the amount of absorbed power. During the lasing process, the total of absorbed power in the Nd:YAG crystal is obtained around 5.8-W with the 7.6-W incident power by measuring the thermal cooling power of the gain medium. The slope efficiency of the Nd:YAG NPRO laser is obtained of 78.7% experimentally, which approaches the quantum limit of 79% theoretically. This newly realized feature in the Nd:YAG NPRO laser allows for increased energy efficiency and hence less demanding on the heat management, a feature that is especially relevant to laser power upgrade in the ground-based gravitational wave detectors as well as developing laser sources for space-borne gravitational wave detectors.
We present a narrow linewidth laser by optical feedback from a high-finesse F-P cavity. The cavity transmission feeds
back to the laser diode by the external ring path. With a low servo bandwidth system, the feedback phase is compensated
for maintaining the optical feedback operation. The linewidth of the optical feedback laser is reduced to 100 Hz, and the
laser frequency noise in frequency range of 1 Hz to 10 kHz is suppression over 50 dB. It experimentally demonstrates
the excellent characteristics of optical feedback technique.
The recent evaluation of the second cesium fountain NIM5 at National Institute of Metrology(NIM) shows a total
relative uncertainty of 2×10-15. The strontium optical clock project has successfully transferred atoms from broad line
cooling to narrow line cooling. About 10788Sr atoms have been cooled down to 2uK, ready to be loaded into 1
dimensional (1D) optical lattice. The clock transition interrogation laser is locked to a horizontally oriented high finesse
cavity. The linewidth of this laser is reduced to 100Hz level. A fiber based optical frequency comb is being built, which
can be used to synthesize ultra-stable microwave frequency for the fountains in the future.
We in this paper report the progress on developing a "laser cooled Cs atomic fountain clock" at NIM. We also present scheme of the "femto-second pulse laser —comb frequencies" which was just started at NIM. As the f-second comb links optical wavelengths to Cs standard frequency and considering that our new Cs fountain clock is desired to achieve an uncertainty in the order of 10-15, these two projects are expected to advance the capability of optical wavelength measurements in this country to a new level in the near future. This work will also lay the technical foundation for developing optical clock as possible candidate for next generation of frequency standard. Key words: wavelength standard, frequency standard, Cesium clock, comb optical frequency.
In Dense Wavelength Division Multiplexing (DWDM) fiber communication system, more and more channels have to be put into a single fiber in order to fulfil the ever-increasing demand for high capacity. This put strict requirements on the wavelength characteristics of various active and passive optical components. Generally speaking, in current DWDM system, a wavelength accuracy of 5pm is necessary for analyzing channel performance, and 0.5 pm is required for the aging test of components. An extended cavity laser diode (ECLD) frequency stabilized to saturated absorption lines of acetylene C2H2 with a potential long term frequency stability of 10-12 can provide excellent wavelength reference for DWDM communication system[1][2][3]. In this paper, we describe a practical 1.5µm wavelength transfer standard based on C2H2 stabilized DFB laser and tunable fiber Fabry-Perot etalon[4]. This transfer standard is suitable for the calibration of widely used optical spectrum analyzers (OSA) and wavelength/multi-wavelengths meters. This device is currently under development in the Quantum Division ofNational Institute of Metrology (NIM).
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