High performance vapour-cell frequency standards
2015-10-27, Gharavipour, Mohammadreza, Affolderbach, Christoph, Kang, Songbai, Bandi Nagabhushan, Thejesh, Gruet, Florian, Pellaton, Matthieu, Mileti, Gaetano
We report our investigations on a compact high-performance rubidium (Rb) vapour-cell clock based on microwave-optical double-resonance (DR). These studies are done in both DR continuous-wave (CW) and Ramsey schemes using the same Physics Package (PP), with the same Rb vapour cell and a magnetron-type cavity with only 45 cm3 external volume. In the CW-DR scheme, we demonstrate a DR signal with a contrast of 26% and a linewidth of 334 Hz; in Ramsey-DR mode Ramsey signals with higher contrast up to 35% and a linewidth of 160 Hz have been demonstrated. Short-term stabilities of 1.4×10^-13 τ^-1/2 and 2.4×10^-13 τ^-1/2 are measured for CW-DR and Ramsey-DR schemes, respectively. In the Ramsey-DR operation, thanks to the separation of light and microwave interactions in time, the light-shift effect has been suppressed which allows improving the long-term clock stability as compared to CW-DR operation. Implementations in miniature atomic clocks are considered.
Laser-pumped paraffin-coated cell rubidium frequency standard
, Bandi Nagabhushan, Thejesh, Affolderbach, Christoph, Mileti, Gaetano
We have realized and studied a rubidium atomic frequency standard based on a paraffin-coated cell, exhibiting a short-term frequency stability <3 × 10−12 τ−1/2 between τ = 1 and 100 s. Characterization of the wall-coating is performed by measuring the T1and T2 relaxation times. Perturbations of the medium- to long-term clock stability, due to variations in the laser-intensity, laser frequency, the microwave power shift, and the shifts due to temperature variations are measured and analyzed. A method for reducing the intensity light-shift by detuning the laser frequency and the resulting improvement in clock stability is demonstrated. This work is of relevance for further improvements on Rb cell standards using anti-relaxation wall-coating technology.
Compact microwave cavity for high performance rubidium frequency standards
, Stefanucci, Camillo, Bandi Nagabhushan, Thejesh, Merli, Francesco, Pellaton, Matthieu, Affolderbach, Christoph, Mileti, Gaetano, Skrivervik, Anja K.
The design, realization, and characterization of a compact magnetron-type microwave cavity operating with a TE011-like mode are presented. The resonator works at the rubidium hyperfine ground-state frequency (i.e., 6.835 GHz) by accommodating a glass cell of 25 mm diameter containing rubidium vapor. Its design analysis demonstrates the limitation of the loop-gap resonator lumped model when targeting such a large cell, thus numerical optimization was done to obtain the required performances. Microwave characterization of the realized prototype confirmed the expected working behavior. Double-resonance and Zeeman spectroscopy performed with this cavity indicated an excellent microwave magnetic field homogeneity: the performance validation of the cavity was done by achieving an excellent short-term clock stability as low as 2.4 × 10−13τ−1/2. The achieved experimental results and the compact design make this resonator suitable for applications in portable atomic high-performance frequency standards for both terrestrial and space applications.
High performance vapour-cell frequency standards
2016-6-1, Gharavipour, Mohammadreza, Affolderbach, Christoph, Kang, Songbai, Bandi Nagabhushan, Thejesh, Gruet, Florian, Pellaton, Matthieu, Mileti, Gaetano
We report our investigations on a compact high-performance rubidium (Rb) vapour-cell clock based on microwave-optical double-resonance (DR). These studies are done in both DR continuous-wave (CW) and Ramsey schemes using the same Physics Package (PP), with the same Rb vapour cell and a magnetron-type cavity with only 45 cm3 external volume. In the CW-DR scheme, we demonstrate a DR signal with a contrast of 26% and a linewidth of 334 Hz; in Ramsey-DR mode Ramsey signals with higher contrast up to 35% and a linewidth of 160 Hz have been demonstrated. Short-term stabilities of 1.4×10-13 τ-1/2 and 2.4×10-13 τ-1/2 are measured for CW-DR and Ramsey-DR schemes, respectively. In the Ramsey-DR operation, thanks to the separation of light and microwave interactions in time, the light-shift effect has been suppressed which allows improving the long-term clock stability as compared to CW-DR operation. Implementations in miniature atomic clocks are considered.
Double-resonance studies on compact, high-performance rubidium cell frequency standards
, Bandi Nagabhushan, Thejesh, Mileti, Gaetano
This thesis presents experimental studies on continuous-wave (CW) laser-microwave double-resonance (DR) spectroscopy and metrology in rubidium (87Rb) vapor cells in view of new high-performance, compact Rb-cell atomic clocks. The Rb vapor cell is confined inside a magnetron-type cavity microwave resonator (MWR). The CW DR spectroscopy involves two resonant electromagnetic fields that are operated simultaneously to interrogate the atoms - the optical field to polarize the atoms by optical pumping, and the microwave field to drive the ground-state hyperfine clock transition that serves as an atomic frequency reference. Details on characterization of compact laser heads and microwave synthesizers used in this work are presented. The vapor cell standards are useful in our everyday lives for applications ranging from telecommunications, navigation, metrology etc.
In view of improving the performances of the Rb cell standards, two different clock approaches were studied in detail:
The first one is on use of vapor cells (1.4 cm3) whose inner walls are coated with anti-relaxation material. A first ever wall-coated cell clock was demonstrated with good short-term frequency stability. The medium- to long-term stability was found to be limited by the temperature coefficient (TC) of the coating material itself. This work gave the insight to important features to be considered in future anti-relaxation coating materials for atomic standards.
The second novel approach involves using a bigger cell (12 cm3) within a newly developed, improved MWR towards a high-performance atomic standard. Adopting a larger cell gives a higher atomic Q-factor signal that improves the short-term clock stability. In this approach, the cell was filled with 87Rb and buffer gases. With this clock, we demonstrate the state-of-the-art short-term stability of <1.4×10−13 τ−1/2. Metrological quantitative measurements on parameters influencing the medium- to long-term stability were studied in view of next generation satellite navigation systems that demand a stability level of <1×10−14 at 10 4 s (equivalent to <1 ns/day). The potential of short-term stability and understanding of the limiting factors on medium- to long-term time scales demonstrated in this study pave the way for future work towards the commercialization of high-performance Rb atomic clocks for a variety of applications.
Imaging the Static Magnetic Field Distribution in a Vapor Cell Atomic Clock
2015-4-12, Affolderbach, Christoph, Du, Guan-Xiang, Bandi Nagabhushan, Thejesh, Horsley, Andrew, Treutlein, Philipp, Mileti, Gaetano
We use a Ramsey-type interaction scheme to measure spatially-resolved images of the static magnetic field (C-field) amplitude Bdc applied across the Rb cell in the physics package of a high-performance vapor-cell atomic clock. Low field variations of <; 0.5% are found across the recorded images, and Fourier analysis of the data indicates low variations of Bdc also along the direction of laser propagation. Images of the T2 relaxation time are obtained in a similar way, and show a distribution that correlates with the Bdc distribution. This indicates inhomogeneous dephasing due to C-field gradients, which also results in spatial variation of the T2 time for the clock transition.
ac Stark shift in double resonance and coherent population trapping in a wall-coated cell for compact Rb atomic clocks
, Miletic, Danijela, Bandi Nagabhushan, Thejesh, Affolderbach, Christoph, Mileti, Gaetano
We present a comparative study of the light-shifts (ac Stark shift) in a Rb vapour cell using two possible schemes for Rb atomic clocks: double resonance (DR) and coherent population trapping (CPT). For both schemes, the same wall-coated cell in a compact atomic resonator was used. The light-shift resulting from a monochromatic (DR) or a non-monochromatic (CPT) optical excitation was measured as a function of the laser intensity and the laser frequency and compared with existing theoretical results.
Compact high-performance continuous-wave double-resonance rubidium standard with 1.4 x 10 -13 -1/2 stability
2014-11-6, Bandi Nagabhushan, Thejesh, Affolderbach, Christoph, Mileti, Gaetano, Skrivervik, A.K., Stefanucci, Camillo, Merli, Francesco
We present our studies on a compact high-performance continuous wave (CW) double-resonance (DR) rubidium frequency standard in view of future portable applications. Our clock exhibits a short-term stability of 1.4 × 10 -13 τ -1/2 , consistent with the short-term noise budget for an optimized DR signal. The metrological studies on the medium- to longterm stability of our Rb standard with measured stabilities are presented. The dependence of microwave power shift on light intensity, and the possibility to suppress the microwave power shift is demonstrated. The instabilities arising from the vapor cell geometric effect are evaluated, and are found to act on two different time scales (fast and slow stem effects). The resulting medium- to long-term stability limit is around 5.5 × 10 -14 . Further required improvements, particularly focusing on medium- to long-term clock performance, are discussed.
High-performance laser-pumped rubidium frequency standard for satellite navigation
2011, Bandi Nagabhushan, Thejesh, Affolderbach, Christoph, Calosso, C.E., Mileti, Gaetano
Presented is a double-resonance continuous-wave laser-pumped rubidium (Rb) atomic clock with a short-term stability of 4×10−13 τ −1/2 for integration times 1 s ≤ τ ≤ 1000 s, and a medium- to long-term stability reaching the 1×10−14 level at 104 s. The clock uses an Rb vapour cell with increased diameter of 25 mm, accommodated inside a newly developed compact magnetron-type microwave cavity. This results in a bigger signal with reduced linewidth, and thus improved short-term stability from a clock with 1 dm3 physics package volume only. The medium- to long-term clock stability is achieved by minimising the effects of light-shift and temperature coefficient on the atoms. Potential applications of the clock are discussed.
Imaging microwave and DC magnetic fields in a vapor-cell Rb atomic clock
2015-11-6, Affolderbach, Christoph, Du, Guan-Xiang, Bandi Nagabhushan, Thejesh, Horsley, Andrew, Treutlein, Philipp, Mileti, Gaetano
We report on the experimental measurement of the dc and microwave magnetic field distributions inside a recently developed compact magnetron-type microwave cavity mounted inside the physics package of a high-performance vapor-cell atomic frequency standard. Images of the microwave field distribution with sub-100-μm lateral spatial resolution are obtained by pulsed optical-microwave Rabi measurements, using the Rb atoms inside the cell as field probes and detecting with a CCD camera. Asymmetries observed in the microwave field images can be attributed to the precise practical realization of the cavity and the Rb vapor cell. Similar spatially resolved images of the dc magnetic field distribution are obtained by Ramsey-type measurements. The T2 relaxation time in the Rb vapor cell is found to be position dependent and correlates with the gradient of the dc magnetic field. The presented method is highly useful for experimental in situ characterization of dc magnetic fields and resonant microwave structures, for atomic clocks or other atom-based sensors and instrumentation.