Accuracy evaluation of an optically pumped caesium beam frequency standard KRISS-1

Abstract

We report on Korea's first optically pumped primary frequency standard (KRISS-1) developed at the Korea Research Institute of Standards and Science. Although a relatively small microwave cavity (the cavity drift region is about 36 cm in length) has been employed in this experiment, we achieved our desired frequency accuracy by applying the regularized inverse on the Ramsey spectrum analysis and compensating the effect of the evanescent field inside the cavity. KRISS-1 typically performs at a short term stability of 1.3 × 10 −12 / √ τ with a combined uncertainty of 1.0 × 10 −14 .

Periodic-Error-Free All-Fiber Distance Measurement Method With Photonic Microwave Modulation Toward On-Chip-Based Devices

“…It was modulated by an intensity modulator (LN05S-FC, Thorlabs) (IM #1) driven at 15 GHz, corresponding to an ambiguity distance of 9.993 mm. A microwave synthesizer (SynthHD PRO, Windfreak Technologies, LLC) to drive the intensity modulator was referenced to a cesium atomic clock with a frequency uncertainty of 10 -13 , [30] which gave direct traceability to a length standard. The modulated beam was divided into the reference and measurement beams by a fiber coupler with a 9:1 split ratio.…”

“…As a counterpart to laser displacement interferometry, absolute distance measurements have been proposed and realized by various approaches [6,7], including the time-of-flight method [8,9], amplitude modulation ranging [10][11][12][13][14], frequency modulation ranging [15][16][17], spectral resolved interferometry [18][19][20], multi-wavelength interferometry [21][22][23], dual-comb ranging [24][25][26], and microcomb ranging [27][28][29]. One of these examples is LIDAR (light detection and ranging), which works with the time-offlight method [30].…”

Improvement of Frequency Locking Algorithm for Atomic Frequency Standards

“…For an ideal gain, i.e., g ¼ 1, the two servos converge immediately so that after two seconds (i.e., one modulation period) the frequency errors remain exactly zero both for method I and II as it can be seen from eqs. ( 5) and (10). The servo needs to converge immediately in order for the frequency data recorded by the servo to be a real-time comparison between the hydrogen maser and KRISS-1.…”

“…A digital servo based on a personal computer is advantageous for the development of an atomic frequency standard [1][2][3][4][5][6][7][8][9][10][11] because it can provide a variety of sequenced control over the equipments and diverse processing techniques on the measured data. One of the important role of the digital servo is to lock the microwave frequency to the center of the clock transition signal.…”

“…7,8,11) In this paper we propose a new algorithm and compare it with the old one that had been used for the optically pumped cesium atomic beam frequency standards such as NIST-7 8) and KRISS-1. [10][11][12][13][14][15][16] The new algorithm exploiting twice as frequent feedback as the old one can reduce the frequency noise transformed from special types of signal noise such as flicker noise and random-walk noise. To characterize the two methods we first check how fast the servos can find the center frequency of the Ramsey signal from an initial guess.…”