We report on the generation of a tunable buffer-gas mixture within microfabricated alkali-vapor cells. We show that the combination of low-permeation windows with sequential openings of laser-actuated break seals enables adjustment of a He-Ne noble gas mixture, fully compatible with alkali-metal dispensers. The gas reservoirs and the main cell cavities are initially sealed at the wafer level under distinct helium and neon atmospheres, respectively. Within each cell, after Cs vapor is released from the dispenser, the break seals are successively actuated to incrementally increase the helium fraction in the buffer-gas mixture. This process shifts the atomic clock frequency inversion temperature toward higher values. As an illustration, one of the fabricated cells was operated at 95 degrees C in a coherent population trapping clock, achieving a fractional frequency stability of 9 x 10-11 at an integration time of 1 day. These results demonstrate the feasibility of precisely tuning buffer-gas compositions in microfabricated vapor cells and support the suitability of He-Ne mixtures for miniature atomic clock applications.

OBJECTIVE:To evaluate whether autofluorescence spectroscopy (AFS) can reliably distinguish cholesteatoma from surrounding middle-ear tissues, and to develop a real-time intraoperative diagnostic tool. STUDY DESIGN:Prospective ex vivo study. SETTING:Besançon University Hospital, France (tertiary care center). METHODS:In this prospective ex vivo study, middle-ear tissue biopsies were collected during cholesteatoma surgeries and analyzed using autofluorescence following 405-nm laser excitation. Each sample was classified based on its spectral signature and confirmed by histopathology. A computer-assisted model was applied to differentiate cholesteatoma from noncholesteatoma tissues, and its performance was assessed using standard cross-validation. RESULTS:Thirty-six tissue samples from 23 patients were analyzed, generating nearly 3800 fluorescence spectra. The model correctly classified all samples, achieving 94.5% accuracy, 94.7% sensitivity, and 94.2% specificity. The system provided consistent performance across tissue types and returned results in real time, with a response time of 0.1 seconds per sample. Each output included a probability score indicating the likelihood of cholesteatoma presence. CONCLUSION:AFS demonstrated high accuracy in distinguishing cholesteatoma from other middle-ear tissues. Its speed, simplicity, and probabilistic feedback suggest strong potential for real-time intraoperative use. Once validated in vivo, this technology could assist surgeons by improving tissue discrimination and potentially reducing recurrence rates.

A metasurface-based wide-band (400-1500nm) blazed grating is modeled by in-house Finite Element model with 3D topology optimization, leading to a pillar-structure exhibiting 57% average diffraction efficiency over the 2-octave band.

We summarize recent activities performed at FEMTO-ST on the development of high-stability clocks and references based on hot alkali vapor microfabricated vapor cells. By combining pulsed Ramsey-based interrogation protocols and cells built with low-permeation glass wafers, CPT-based microwave clocks with stability in the low 10–12 range at 1 day were demonstrated. We also report on optical references that rely on sub-Doppler spectroscopy techniques. These standards currently exhibit short-term stabilities of a few 10–13 at 1 s. Those microwave and optical standards might be of significant interest for next-generation navigation, communications and instrumentation systems.

We report on the development and short-term stability characterization of an optical frequency reference based on the spectroscopy of the rubidium two-photon transition at 778 nm in a microfabricated vapor cell. When compared against a 778 nm reference signal extracted from a frequency-doubled cavity-stabilized telecom laser, the short-term stability of the microcell frequency standard is 3.5 x 10-13 tau - 1 / 2 until 200 s, in good agreement with a phase noise level of + 43 dBrad2/Hz at 1 Hz offset frequency. The two main contributions to the short-term stability of the microcell reference are currently the photon shot noise and the intermodulation effect induced by the laser frequency noise. Retaining a relevant margin of progress, these results show the interest of this spectroscopic approach for the demonstration of high-stability miniaturized optical vapor cell clocks. Such clocks are poised to be highly beneficial for applications in navigation, communications, and metrology. (c) 2024 Optica Publishing Group. All rights, including for text and data mining (TDM), Artificial Intelligence (AI) training, and similar technologies, are reserved.

We present a coherent-population trapping (CPT) microcell atomic clock using symmetric auto-balanced Ramsey (SABR) spectroscopy. The pulsed SABR sequence is applied through direct current-based power modulation of the vertical-cavity surface-emitting laser, eliminating the need for an external optical shutter and enabling compatibility with fully-integrated clocks. The sequence is controlled by a single FPGA-based digital electronics board. A key aspect of proper clock operation was the implementation of a real-time tracking of the atomic signal detection window. The clock frequency dependence on laser power, microwave power, laser frequency, and timing of the detection window has been measured, obtaining sensitivity coefficients lower than those obtained with Ramsey-CPT spectroscopy. The Allan deviation of the SABR-CPT clock, based on a microfabricated cell with low-permeation glass windows, is 8 × 10-10 at 1 s and averages down in the 10-12 range at 1 day. These results might stimulate the development of chip-scale atomic clocks using Ramsey-based sequences, with reduced light-shift sensitivity, and enhanced long-term stability performances.

We describe the short-term frequency stability characterization of external-cavity diode lasers stabilized onto the 6S1/2-7P1/2 transition of Cs atoms at 459 nm, using a microfabricated vapor cell. The laser beatnote between two nearly identical systems, each using saturated absorption spectroscopy in a simple retroreflected configuration, exhibits an instability of 2.5 x 10(-13 )at 1 s, consistent with phase noise analysis, and 3 x 10(-14 )at 200 s. The primary contributors to the stability budget at 1 s are the FM-AM noise conversion and the intermodulation effect, both emerging from laser frequency noise. These results highlight the potential of microcell-based optical references to achieve stability performances comparable to that of an active hydrogen maser in a remarkably simple architecture.

A topology optimized metasurface grating is presented, designed using a 3D, in-house developed Finite Element model. It is manufacturable and exhibits nearly 60% of average diffraction efficiency on the -1st order between 400 and 1500 nm.

Microfabricated alkali vapor cells are key to enable miniature devices such as atomic clocks and optically pumped magnetometers with reduced size, weight, and power. Yet, more versatile fabrication methods are still needed to further expand their use cases. Here, we demonstrate an approach to collectively fill and seal microfabricated cesium cells using locally sealed microchannels patterned within one of the glass substrates comprising the cells. Unlike current methods that rely on wafer-level anodic bonding as the last sealing step, an approach based on local sealing opens the path to features so far limited to traditional glass-blown cells, including the ability to deposit temperature-sensitive antirelaxation coatings, reaching lower background gas pressure without an additional gettering material or filling with diverse atomic or molecular species.

We report on the operation of a coherent population trapping (CPT) microcell atomic clock using a pulsed Ramsey-like interrogation. The Ramsey-CPT sequence, defined by two-step optical pulses separated by a free-evolution dark time, is produced by switching on and off the output power of a low-power vertical-cavity surface-emitting laser, through direct modulation of its driving current. High-contrast and narrow Ramsey-CPT fringes are detected without the use of any external optical modulator stage. We demonstrate closed-loop operation of the clock based on high-speed digital signal processing implemented in a field programmable gate array board. The clock's short-term fractional frequency stability is 1.3 × 10−10τ−1/2 until 2000 s. A power light-shift coefficient of 8 × 10−11/μW, in relative value, is obtained for a dark time of 150 μs. This value is about ten times lower than in the continuous regime. These results show the feasibility of fully integrated atomic clocks based on Ramsey spectroscopy, which could provide enhanced long-term stability.

We report on the characterization of sub-Doppler resonances detected by probing the 6S 1/2 - 7P 1/2 transition of the Cs atom at 459 nm in a microfabricated vapor cell. The dependence of the sub-Doppler resonance (linewidth, amplitude) on some key experimental parameters, including the laser intensity and the cell temperature, is investigated. These narrow atomic resonances are of interest for high-resolution spectroscopy and instrumentation and may constitute the basis of a high-stability microcell optical standard.

Sub-wavelength blazed gratings designed using topology optimization are presented. They diffract light on a particular order with a very high diffraction efficiency, on a broad wavelength range in the visible and near-infrared light. They are moreover faced with preliminary results of manufacturing of metasurfaces.

Stability and precision of atomic devices are closely tied to the quality and stability of the internal atmosphere of the atomic vapor cells on which they rely. Such atmosphere can be stabilized by building the cell with low permeation materials such as sapphire, or aluminosilicate glass in microfabricated devices. Recently, we showed that permeation barriers made of Al$_{2}$O$_{3}$ thin-film coatings deposited on standard borosilicate glass could be an alternative for buffer gas pressure stabilization. In this study, we hence investigate how helium permeation is influenced by the thickness, ranging from 5 to 40 nm, of such Al$_{2}$O$_{3}$ thin-films coated by atomic layer deposition. Permeation rates are derived from long-term measurements of the pressure-shifted transition frequency of a coherent population trapping (CPT) atomic clock. From thicknesses of 20 nm onward, a significant enhancement of the cell hermeticity is experienced, corresponding to two orders of magnitude lower helium permeation rate. In addition, we test cesium vapor cells filled with neon as a buffer gas and whose windows are coated with 20 nm of Al$_{2}$O$_{3}$. As for helium, the permeation rate of neon is significantly reduced thanks to alumina coatings, leading to a fractional frequency stability of 4x10$^{-12}$ at 1 day when the cell is used in a CPT clock. These features outperform the typical performances of uncoated Cs-Ne borosilicate cells and highlight the significance of Al$_{2}$O$_{3}$ coatings for buffer gas pressure stabilization.

The combination of atomic spectroscopy, integrated photonics, and microelectromechanical systems leads the way to the demonstration of microcell-based optical atomic clocks. Here, we report the short-term stability budget of table-top Cs microcell-stabilized lasers based on dual-frequency sub-Doppler spectroscopy (DFSDS). The dependence of the sub-Doppler resonance properties on key experimental parameters is studied. The detection noise budget and absolute phase noise measurements are in good agreement with the measured short-term frequency stability of the laser beatnote, at the level of 1.1 × 10 − 12 τ − 1 / 2 until 100 s, currently limited by the intermodulation effect from a distributed-feedback laser setup. The fractional frequency stability of the laser beatnote at 1 s is about 100 times greater than that of commercial microwave chip-scale atomic clocks and validates interest in the DFSDS approach for the development of high-performance microcell-based optical standards.

The stability and accuracy of atomic devices can be degraded by the evolution of their cell inner atmosphere. Hence, the undesired entrance or leakage of background or buffer gas, respectively, that can permeate through the cell walls, should be slowed down. In this work, we investigate helium permeation in microfabricated alkali vapor cells filled with He and whose windows are made of borosilicate glass (BSG) or aluminosilicate glass (ASG). The permeation is then derived from routine measurements of the pressure-shifted hyperfine transition frequency of an atomic clock. We first confirm that ASG reduces the He permeation rate by more than two orders of magnitude, in comparison to BSG. In addition, we demonstrate that Al2O3 thin-film coatings, known to avoid alkali consumption in vapor cells, can also significantly reduce He permeation. The permeation through BSG is thereby reduced by a factor up to 130, whereas the one through ASG is decreased by a factor up to 5.0 compared to uncoated substrates. These results may contribute to the development of miniaturized atomic clocks and sensors with improved long-term stability or sensitivity.

We report on the characterization of sub-Doppler resonances detected by probing the 6S$_{1/2}$-7P$_{1/2}$ transition of Cs atom at 459 nm in a microfabricated vapor cell. The dependence of the sub-Doppler resonance (linewidth, amplitude) on some key experimental parameters, including the laser intensity and the cell temperature, is investigated. These narrow atomic resonances are of interest for high-resolution spectroscopy, instrumentation, and may constitute the basis of a near-UV microcell optical standard.