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.

Analysis of the mode composition of an X-band overmoded O-type Cerenkov high-power microwave oscillator Phys. Plasmas 19, 103102 (2012) Gap independent coupling into parallel plate terahertz waveguides using cylindrical horn antennas J. Appl. Phys. 112, 073102 (2012) A band-pass filter approach within molecular dynamics for the prediction of intrinsic quality factors of nanoresonators J. Appl. Phys. 112, 074301 (2012) A research of W-band folded waveguide traveling wave tube with elliptical sheet electron beam Phys. Plasmas 19, 093117 (2012) Additional information on Rev. Sci. Instrum. The design, realization, and characterization of a compact magnetron-type microwave cavity operating with a TE 011 -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 −13 τ −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.

Presented is a double-resonance continuous-wave laser-pumped rubidium (Rb) atomic clock with a short-term stability of 4 × 10 213 t 21/2 for integration times 1 s ≤ t ≤ 1000 s, and a medium-to longterm stability reaching the 1 × 10 214 level at 10 4 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 dm 3 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.Motivation: Portable and compact atomic clocks are today indispensable for many aspects of human civilisation [1], with increasing demand for better clock precision and stability [2,3]. Application examples of such frequency standards include precise navigation, telecommunication, and space science [1,[3][4][5]. Laboratory clocks like primary caesium (Cs) fountains and optical clocks exhibit excellent stabilities of s y (t) ≤ 1 × 10 213 t 21/2 , but are bulky and expensive. Even cold atom clocks or optical clocks proposed for space applications target outlines of 1 m 3 volume, 230 kg mass, and 450 W power consumption [5]; hence a trade-off must be made between stability and portability. Recently developed portable standards, such as the passive hydrogen maser (SPHM) [4] or laser-pumped Cs beam clocks (LPCs) [6], exhibit a reasonable trade-off with volume (13 , V , 28 dm 3 ), mass (8 , m , 18 kg), power consumption (30 , P , 80 W) and stability (7 × 10 213 , s y (1 s) , 1.5 × 10 212 and 1 × 10 214 , s y (10 4 s) , 3 × 10 214 ). Here we show that our simple and compact, continuouswave (CW) laser-pumped double-resonance (DR) Rb clock stability outperforms that of LPCs standards up to 1000 s, and is comparable to coldatom portable clocks [3] or the SPHM, but from a physics package (PP) with volume of ,1 dm 3 only in our case. A previous laser-pumped Rb clock based on a magnetron-type cavity had a stability of s y ≃ 3 × 10 212 t 21/2 [7]. By increasing the cell diameter to 25 mm and redesign of the magnetron cavity, we improve on this clock stability while maintaining a very compact volume of the magnetron-type resonator. This clock can have applications in, e.g., next generation satellite navigation systems like GALILEO. In particular, a short-term stability of 6 × 10 213 t 21/2 allows reaching the 1 × 10 214 level already at timescales of 3600 s, well before the 6000 s relevant for clock error prediction and synchronisation.

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 T 2 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.

For laser micro processing with short and ultra-short pulses the threshold fluence is affected by the incubation and changes with the number of pulses applied. In general the incubation effect is described by a power function including the incubation coefficient S. Beside the threshold fluence also the energy penetration depth is subject to the incubation effect; moreover it is a main cause for the change of the threshold fluence with increasing pulse number.The behavior of the threshold fluence can be explained by varying absorption (due to changes in the surface reflectivity), chemical changes of the surface (e.g. due to oxidation) or changes in the microstructure of the material whereas the behavior of the energy penetration depth could be explained by the latter two effects but should not be affected by a change in the absorption. To try to distinguish between these three effects a systematic ablation study with 10 ps pulses at 1064nm wavelength on copper and iron under different gases atmospheres and pressures was done.The results show on the one hand the change of the energy penetration depth is the main cause of the incubation and that on the other hand an adapted model better fits the trend of the threshold fluence and the penetration depth as a function of the number of pulses applied. The influence of the gas (air, oxygen, nitrogen and argon) is only marginal whereas a reduction of the pressure from normal atmosphere down to 50 mbar results in a 25% increase of the maximum removal rate. Induced changes in the microstructure were detected by a high resolution X-ray diffraction analysis on single crystal (111-orientation) copper and iron samples.

Abstract-We present the development and complete spectral characterization of our compact and frequency-stabilized laser heads, to be used for rubidium atomic clocks and basic spectroscopy. The light source is a Distributed Feed-Back (DFB) laser diode emitting at 780 nm or 795 nm. The laser frequency is stabilized on a sub-Doppler absorption peak of the 87 Rb atom, obtained from an evacuated rubidium cell. These laser heads, including the electronics for the light signals detection, have an overall volume of 0.63 liters. We also present a variant of the laser head into which is integrated an Acousto-Optical Modulator (AOM) that precisely detunes the laser frequency in order to minimize the AC Stark shift in Rb atomic clocks.

We have realized and studied a rubidium atomic frequency standard based on a paraffin-coated cell, exhibiting a short-term frequency stability <3 Â 10 À12 s À1/2 between s ¼ 1 and 100 s. Characterization of the wall-coating is performed by measuring the T 1 and T 2 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.

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