Voici les éléments 1 - 10 sur 87
- PublicationMétadonnées seulementSub-Doppler diode laser frequency stabilization with the DAVLL scheme on the D1 line of a 87Rb vapor-cellWe established an experimental set-up that allows laser stabilization using the Doppler1 and sub-Doppler2,3 Dichroic Atomic Vapor Laser Locking (DAVLL) and the Saturated Absorption (SA) scheme. In this report we present comparative studies between Doppler and sub-Doppler DAVLL using heterodyne frequency stability measurements with an independently SA stabilized laser. Some major sources of frequency instability are discussed together with ways to improve the stability. Special focus is laid on the sub-Doppler DAVLL stabilization technique where a new approach for getting higher stability is introduced. In our measurements, the 87Rb D1 line was used as reference atomic line.
- PublicationAccès libreCPT Cesium-Cell Atomic Clock Operation With a 12-mW Frequency Synthesizer ASICIn this paper, we present the design, fabrication, and electrical characterization of a low-power microwave source for interrogation of cesium atomic hyperfine transition frequency using the coherent population trapping (CPT) technique. The 4.6-GHz frequency generation and signal buffering is performed by a single-chip frequency synthesizer ASIC with a frequency tuning resolution of 1 x 10^-13 and a programmable RF output power from -10 to 0 dBm. The circuit was used to modulate the current of a vertical-cavity surface-emitting laser through a dedicated impedance matching network and low thermal conductivity transmission line. Strong modulation sidebands with >60% of carrier amplitude were obtained with an ASIC power consumption of 12 mW. The system was used as optical source for atomic interrogation in an experimental cesium CPT clock. The measured clock stability of 5 x 10^-11 at τ = 1 s, going down to 4.5 x 10^-12 at τ = 200 s, is limited by the signal-to-noise ratio of the detected CPT signal.
- PublicationAccès libreLow-temperature indium-bonded alkali vapor cell for chip-scale atomic clocksA low-temperature sealing technique for micro-fabricated alkali vapor cells for chip-scale atomic clock applications is developed and evaluated. A thin-film indium bonding technique was used for sealing the cells at temperatures of ≤140 °C. These sealing temperatures are much lower than those reported for other approaches, and make the technique highly interesting for future micro-fabricated cells, using anti-relaxation wall coatings. Optical and microwave spectroscopy performed on first indium-bonded cells without wall coatings are used to evaluate the cleanliness of the process as well as a potential leak rate of the cells. Both measurements confirm a stable pressure inside the cell and therefore an excellent hermeticity of the indium bonding. The double-resonance measurements performed over several months show an upper limit for the leak rate of 1.5 × 10−13 mbar•l/s. This is in agreement with additional leak-rate measurements using a membrane deflection method on indium-bonded test structures.
- PublicationMétadonnées seulementLong-Term Stability Analysis Towards < 10-14 Level for a Highly Compact POP Rb Cell Atomic ClockLong-term frequency instabilities in vapor-cell clocks mainly arise from fluctuations of the experimental and environmental parameters that are converted to clock frequency fluctuations via various physical processes. Here, we discuss the frequency sensitivities and the resulting stability limitations at one day timescale for a rubidium vapor-cell clock based on a compact magnetron-type cavity operated in air (no vacuum environment). Under ambient laboratory conditions, the external atmospheric pressure fluctuations may dominantly limit the clock stability via the barometric effect. We establish a complete long-term instability budget for our clock operated under stable pressure conditions. Where possible, the fluctuations of experimental parameters are measured via the atomic response. The measured clock instability of < 2·E10.14 at one day is limited by the intensity light-shift effect, which could further be reduced by active stabilization of the laser intensity or stronger optical pumping. The analyses reported here show the way towards simple, compact, and low-power vapor-cell atomic clocks with excellent long-term stabilities. ≤ 10.14 at one day when operated in ambient laboratory conditions.
- PublicationAccès libreFrequency-stabilised laser reference system for trace-gas sensing applications from spaceA four-wavelength low-power continuous-wave frequency laser reference system has been realised in the 935.4-nm range for water vapour differential absorption lidar (DIAL) applications. The system is built around laboratory extended-cavity and DFB diode lasers. Three lasers are directly locked to three water vapour absorption lines of different strength, whereas the wavelength of the fourth laser lies out of any absorption line (offline). On-line stabilisation is performed by wavelength modulation spectroscopy technique, while precise offline stabilisation is realised by an offset locking at 18.8 GHz. Offset frequency larger than 320 GHz has also been demonstrated at 1.55 μm, based on an all-fibre optical frequency comb. First steps towards the use of a photonic crystal fibre as ultra compact reference cell with long optical pathlength were realised. The developed techniques for direct and offset-lock laser stabilisation can also be applied to other gases and wavelengths, provided the required optical components are available for the laser wavelength considered.
- PublicationAccès libreCPT Cesium-Cell Atomic Clock Operation with a 12-mW Frequency Synthesizer ASIC
;Zhao, Yazhou ;Tanner, Steve ;Casagrande, Arnaud ; ;Schneller, Luc ;Mileti, and GaetanoFarine Pierre-AndréIn this paper, we present the design, fabrication, and electrical characterization of a low-power microwave source for interrogation of cesium atomic hyperfine transition frequency using the coherent population trapping (CPT) technique. The 4.6-GHz frequency generation and signal buffering is performed by a single-chip frequency synthesizer ASIC with a frequency tuning resolution of 1 x 10-13 and a programmable RF output power from -10 to 0 dBm. The circuit was used to modulate the current of a vertical-cavity surface-emitting laser through a dedicated impedance matching network and low thermal conductivity transmission line. Strong modulation sidebands with > 60% of carrier amplitude were obtained with an ASIC power consumption of 12 mW. The system was used as optical source for atomic interrogation in an experimental cesium CPT clock. The measured clock stability of 5 x 10-11 at τ = 1 s, going down to 4.5x10-12 at τ = 200 s, is limited by the signal-to-noise ratio of the detected CPT signal.
- PublicationMétadonnées seulementA compact, frequency stabilized laser head for space RB clocks and wavelength referencesWe present our ongoing development of a compact (<1.5 liters) and high-performance (10-14 at 104 s) laser-pumped Rubidium clock for space applications like, e.g., satellite navigation systems (GALILEO). A compact laser head was developed that includes frequency stabilization of the pump light to a reference cell. Recent clock stability results obtained with this laser head reach 2⋅10-13 at 1000s, limited mainly by residual cell temperature coefficients and light shift effects. We discuss strategies to overcome these limitations and the relationship between the stabilities of the pump laser and the clock. Comparisons of the laser and clock frequency stabilities are presented for stabilization to both Doppler and sub-Doppler spectroscopy.
- PublicationAccès libreMetrological characterization of custom-designed 894.6 nm VCSELs for miniature atomic clocksWe report on the characterization and validation of custom-designed 894.6 nm vertical-cavity surface-emitting lasers (VCSELs), for use in miniature Cs atomic clocks based on coherent population trapping (CPT). The laser relative intensity noise (RIN) is measured to be 1×10−11 Hz−1 at 10 Hz Fourier frequency, for a laser power of 700 μW. The VCSEL frequency noise is 1013 ƒ −1 Hz2/Hz in the 10 Hz < ƒ < 105 Hz range, which is in good agreement with the VCSEL’s measured fractional frequency instability (Allan deviation) of ≈ 1 × 10−8 at 1 s, and also is consistent with the VCSEL’s typical optical linewidth of 20–25 MHz. The VCSEL bias current can be directly modulated at 4.596 GHz with a microwave power of −6 to +6 dBm to generate optical sidebands for CPT excitation. With such a VCSEL, a 1.04 kHz linewidth CPT clock resonance signal is detected in a microfabricated Cs cell filled with Ne buffer gas. These results are compatible with state-of-the-art CPT-based miniature atomic clocks exhibiting a short-term frequency instability of 2–3×10−11 at τ = 1 s and few 10−12 at τ = 104 s integration time.
- PublicationAccès libreLight-shift suppression in laser optically pumped vapour-cell atomic frequency standardsWe present a novel scheme for reducing the AC Stark effect in optical-microwave double-resonance spectroscopy and its application for efficient suppression of the light-shift-related instabilities in laser-pumped gas-cell atomic clocks. The method uses a multi-frequency pump light field that can be easily produced by frequency modulation of the single-frequency pump laser. We show theoretically that variations of the light shift with both laser frequency and light intensity can be strongly suppressed with properly chosen pump light spectra. Suitable modulation parameters can be found for both the case of pure frequency modulation as well as for pump light spectra showing amplitude-modulation contributions, as usually found for current modulation of diode lasers. We experimentally demonstrate the method for a Rb atomic clock using a frequency-modulated distributed Bragg-reflector laser diode as pump light source.
- PublicationMétadonnées seulementNavigating more precisely with laser clocksesa bulletin 122 - may 2005 53Navigating with Laser ClocksSpace-borne atomic frequency standardsare the backbone of today's advancedsatellite navigation and positioningsystems. Rubidium* gas-cell clocks constitutethe ideal frequency standard for this kind ofspace application, since they combine excellentshort- and medium-term stability with smallsize, as well as low weight and powerconsumption. The development of the keytechnologies, particularly in terms of reliablediode lasers and atomic vapour cells, will pavethe way towards low-power and miniature –ultimately chip-scale – atomic clocks forindustrial and domestic use.