# Microfabricated multi-axis cell for integrated atomic devices

L Péroux, A Dewilde, A Mursa, A Mazzamurro, J Bonhomme, Q Tanguy, E

Klinger, L Gauthier-Manuel, O Gaiffe, A. Talbi, et al.

► To cite this version:

L Péroux, A Dewilde, A Mursa, A Mazzamurro, J Bonhomme, et al. Microfabricated multi-axis cell for integrated atomic devices. Journal of Physics: Photonics, 2025, 8 (1), pp.015022. 10.1088/2515-7647/ae2710. hal-05438641

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# Microfabricated multi-axis cell for integrated atomic devices

To cite this article: L Péroux et al 2026 J. Phys. Photonics 8 015022

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Microfabricated multi-axis cell for integrated atomic devices

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L Péroux<fnref n="1" />,*, A Dewilde<fnref n="1" /> ID, A Mursa<fnref n="2" />, A Mazzamurro<fnref n="1" />, J Bonhomme<fnref n="1" /> ID, Q Tanguy<fnref n="2" />, E Klinger<fnref n="2" /> ID,
L Gauthier-Manuel<fnref n="2" />, O Gaiffe<fnref n="2" />, A Talbi<fnref n="1" />, R Boudot<fnref n="2" />, P Pernod<fnref n="1" />, J-F Clément<fnref n="1" />, V Maurice<fnref n="1" /> ID
and N Passilly<fnref n="2" />,*, ID

E-mail: linda.peroux@centralelille.fr and nicolas.passilly@femto-st.fr

**Keywords:** alkali vapor cells, multiple optical channels, wafer-level, optically pumped magnetometers

Abstract

Microfabricated alkali vapor cells enable the miniaturization of atomic sensors, but require collective wafer-level integration of complex features. In many applications—including magnetometers, gyroscopes, magneto-optical traps, and fluorescence imaging—multiple optical accesses are needed to enhance performance. Yet, achieving this without compromising manufacturability remains challenging. In this work, we present a wafer-level fabrication approach that enables three orthogonal optical pathways in microfabricated alkali vapor cells, using fully scalable and collective processes. Our method relies on the thermal reflow of glass preforms, shaped by laser-assisted etching (LAE) and bonded between silicon frames. The relatively low surface roughness produced by LAE allows for effective reflow, which further smooths the surfaces without significantly compromising the optical planarity of the windows. This process results in multi-axis vapor cells featuring embedded, optics-grade lateral windows. We evaluate the device performance through both single-beam and dual-beam atomic magnetometry measurements. Magnetic sensitivities better than 200 fT√Hz⁻<fnref n="1" /> are demonstrated along each of the three orthogonal axes, confirming the potential of the approach for tri-axis magnetic field sensing at sub-picotesla resolution. This fabrication strategy opens new perspectives for versatile, high-performance atomic sensors, fully compatible with wafer-level integration and mass production.

**1. Introduction**

Atomic devices enable highly precise measurements of time, magnetic field or angular velocity. However, their widespread use has been hindered by the cost, size, and scalability of their components. In particular, these devices rely on alkali vapor cells, which were traditionally produced through glassblowing, a process dependent on craftsmanship, making it unsuitable for miniaturization and mass production. In the early 2000s, researchers at NIST pioneered microfabrication techniques for alkali vapor cells, addressing these limitations [11]. Originally developed for the semiconductor industry, microfabrication enables precise structuring of materials at the microscale, allowing the production of compact and low-power atomic systems [8]. The first microfabricated alkali cells quickly led to advancements in chip-scale atomic clocks [9] and magnetometers [21], demonstrating their potential for miniaturized quantum technologies. Beyond miniaturization, microfabrication offers additional advantages, in particular the ability to co-integrate microelectrical features (such as heaters and thermistors) and microoptics, while sustaining greater manufacturability [19]. However, most microfabricated vapor cells are designed with a single optical access, which restricts the use of multi-beam configurations that could enhance their performance or enable additional functionalities. For instance, centimeter-scale glass-blown cells with two optical accesses have demonstrated magnetometry sensitivities as low as 0.6 fT√Hz⁻<fnref n="1" /> [10]. Concerning microfabricated cells, sub-picotesla sensitivity was demonstrated in spin-exchange relaxation free regime but the performance was limited by amplitude noise which could have been suppressed

<footnote n="1">¹ Univ. Lille, CNRS, Centrale Lille, Univ. Polytechnique Hauts-de-France, UMR 8520 - IEMN—Institut d'Electronique de Microélectronique et de Nanotechnologie, Lille, France</footnote>

<footnote n="2">² Université Marie et Louis Pasteur, CNRS, SUPMICROTECH, institut FEMTO-ST, Besançon, France</footnote>

<footnote>* Authors to whom any correspondence should be addressed.</footnote>
using a second probe beam [22]. One solution involves tilting the cell to allow orthogonal pump and
probe beams, leading to 5fT√Hz⁻¹ sensitivity at 200°C [7]. An alternative solution uses superimposed
beams, which has demonstrated sub-picotesla scalar magnetometry [6, 26]. Furthermore, multiple beam
configurations offer additional advantages, for instance by enabling magneto-optical trap (MOT), which
has been demonstrated on microfabricated cells with a 6-beams configuration enabled by the use of a
large window [1]. To further enhance compactness microfabricated grating chips have been combined
with microfabricated cells to realize MOT with a single beam but larger volumes or additional transverse
optical access may be needed [15]. Similarly, terahertz imaging systems based on atomic vapor require
two separate optical paths: one for delivering the pump lasers that excite the atoms, and another for col-
lecting the visible fluorescence used to form the image [3]. Alternative designs have been explored to
overcome these limitations. Spherical glass-blown cells on wafers, developed for gyroscopes [5], allow
multiple optical accesses. However, the non-uniformity of the wall thickness results in distortion of the
transmitted optical beams through the glass-blown structure, restricting its usability in certain applica-
tions. Other approaches exploit integrated reflective surfaces to enable compact optical routing in micro-
fabricated cells [2, 16]. Femtosecond laser machining enabled the fabrication of cells with customizable
3D shapes, which can improve optical access and has already been demonstrated in a single-beam mag-
netometry measurement [12, 25]. More recently, microfabricated atomic vapor cells with multiple optical
channels have been demonstrated using an inner-sidewall molding process [24]. While this approach
improves optical access, its complexity introduces significant fabrication challenges. Here, we propose
a microfabrication process to realize cells with three perpendicular high quality optical accesses at the
wafer-level.

## 2. Microfabricated multi-axis cell

### 2.1. Concept

The multi-axis cell is fabricated from a stack of five wafers: three glass wafers and two silicon wafers (figure 1). This configuration is designed to incorporate a central glass wafer that can be microstructured to provide lateral optical windows. The central glass is bonded between two external glass wafers using intermediate silicon wafers, enabling robust and hermetic anodic bonding-a technique well-established for alkali vapor cell fabrication [8]. This five-wafer structure is employed to achieve higher depths than what can be obtained with deep reactive ion etching (DRIE), as in reference [18]. In our case, the two intermediate silicon wafers also serve as a mechanical frame during the glass reflow process, which is carried out at the wafer-level on the Si-glass-Si sandwich alone. This rigid frame helps maintain the geometry of the etched glass cavities, preventing deformation or collapse during reflow and thereby preserving the flatness of the optical windows. The central glass wafer is structured using laser-assisted wet etching, a technique that offers several advantages. Compared to direct laser ablation, it produces smoother surfaces and vertical (90°) sidewalls, requiring only minor surface correction during reflow to achieve optical quality windows. Additional cavities are etched along the dicing lines to form recessed walls, which undergo the same glass-reflow processing as the main cavities. These recessed features help preserve the optical quality of the outer surfaces of the windows during wafer dicing, thereby eliminating the need for post-polishing. This approach also allows the use of a coarser dicing blade, significantly improving the efficiency of cell release.

### 2.2. Fabrication

The fabrication process, shown in figure 2, begins with the structuring of both the silicon and the central glass wafers. The silicon wafers, 500 µm thick, are processed by optical lithography and DRIE to form cavities that are slightly smaller than those in the glass wafer. This deliberate offset ensures proper edge anchoring of the glass cavities during the subsequent thermal reflow step. These silicon wafers also include narrow channels that connect the dispenser cavity to the science chamber. The 1 mm-thick central borosilicate glass wafer (BOROFLOAT33, SCHOTT, Germany) is structured using laser-assisted etching (LAE). Unlike laser ablation, this method involves direct laser writing only to define the cavity contours, which are then developed by wet etching. By doing so, the sacrificial material does not require to be entirely laser-irradiated but is eventually detached during wet etching in a potassium hydroxide (KOH) aqueous solution. Although KOH is primarily known for anisotropic etching of silicon, its etching rate is significantly enhanced in laser-exposed regions of glass, enabling 3D structuring. Originally proposed in the early 2000s, femtosecond laser pre-irradiation was first used to enhance etching in hydrofluoric acid solutions [13], but higher selectivity was later demonstrated with KOH [14]. The laser writing step is carried out using a f100 aHead Enhanced system (FEMTOprint, Switzerland), where the
<figure><img src="image_4.png" /><figcaption>**Figure 1.** (a) Cell schematic, (b) cell photography.</figcaption></figure>

<figure><img src="image_5.png" /><figcaption>**Figure 2.** Microfabrication flowchart: the central glass substrate, structured by laser-assisted etching (LAE), is sandwiched between two silicon wafers, used first to create a rigid frame during thermal reflow, and secondly, which allow relying on anodic bonding for the cell sealing. External cavities prevent contact with the saw blade during cell release.</figcaption></figure>

glass wafer is mounted horizontally on an XY translation stage. This stage is positioned above a vertically movable 50× microscope objective, which focuses a 1030 nm femtosecond Yb:YAG laser beam into the glass bulk. The LAE process relies on localized structural modifications induced by the intense laser irradiation at the focal point. Etching follows in a 10 mol l⁻¹ KOH solution, maintained at 85 °C under intermittent ultrasonic agitation. The laser-modified regions are etched hundreds of times faster than unexposed glass [20], allowing selective removal with minimal impact on surrounding areas. Unlike laser ablation, the resulting cavity edges remain sharp and clean, enabling bonding without requiring additional surface treatments such as polishing. After etching, the lateral walls of the cavities typically exhibit a surface roughness around 100 nm RMS-significantly smoother than what is usually obtained by laser ablation [24], yet still insufficient for optical-quality surfaces. To improve surface quality, a thermal reflow is performed. The reflow takes place in vacuum (typically a few times 10⁻⁶ mbar), where the temperature is ramped at 6 °C min⁻¹ up to 850 °C (slightly above the glass softening point). The surface is smoothened for 20 min before a controlled cooldown. A 30 min annealing step at 560 °C is added to relieve internal stresses. This reflow process is conducted on a Si-glass-Si stack, pre-assembled by anodic
bonding performed at 350 °C and 900 V. The silicon wafers act as a mechanical frame, ensuring struc-
tural integrity during reflow and preventing the glass corners from collapsing. The silicon cavities are
designed to be nearly 50 µm narrower than their glass counterparts, to reinforce edge anchoring and
accommodate potential bonding misalignments. Final sealing is achieved by anodically bonding two
500 µm thick borosilicate glass wafers onto both sides of the reflowed structure: once the first external
wafer is bonded, the alkali dispensers are loaded into their designated cavity. The second glass wafer
is then bonded in a controlled atmosphere (neon or nitrogen) to complete the cell sealing. Alkali dis-
pensers are then laser-activated at the wafer level. After confirming the presence of saturated alkali vapor
through optical absorption measurements, the cells are released from the wafer by means of saw-dicing.

**2.3. Windows surface characterization**

Unlike DRIE, where sidewall roughness of silicon cavities is typically characterized by scalloping due to
alternating etch/passivation cycles, LAE reveals a different form of periodic surface modulation. In our
case, the vertical sidewalls exhibit a fine, regular texture which corresponds to the successive transla-
tions of the laser focal point, layered sequentially in depth during the irradiation process. The pattern
then arises from the layered voxel-based exposure strategy and is later revealed by differential etching
rates between laser-modified and unmodified glass regions. As a result, the surface quality is orientation-
dependent, with smoother walls typically observed along directions aligned with the laser scanning path.
In the vertical direction, the roughness is generally about 50% higher than in the horizontal direction.

In the following, surface topography and roughness have been measured using an optical profilo-
meter based on white-light interferometry (MSA 500 from Polytec, Waldbronn, Germany), over an
886 × 662 µm² area corresponding to the field of view of a 10 × Mirau objective. As mentioned earlier,
it is noteworthy that the sidewall roughness resulting from wet etching is relatively low compared to sur-
faces produced by direct laser ablation [24]. Additionally, within LAE-processed structures, roughness of
the sidewalls is slightly lower than that observed at the cavity bottom as reported in reference [23], des-
pite the much larger spacing between parallel laser tracks (from 1 µm overlap to 10 µm separation). This
difference stems directly from the ovoid shape of the voxel. In details, reference [23] reported roughness
values of Rq = 45 nm RMS along the writing lines and Rq = 90 nm RMS perpendicular to them, whereas
here, we observe a roughness of Rq = 47 nm RMS along the writing lines and approximately Rq = 64 nm
RMS in the vertical direction.

Nevertheless, in their current state, these surfaces are not smooth enough to transmit laser beams
without introducing distortions, making thermal reflow necessary. Surface annealing is therefore car-
ried out in a tubular furnace (HST1200 by Carbolite) under vacuum conditions. To calibrate the reflow
temperature, a Si-glass-Si structured stack was first fabricated, and diced into chips, which were then
annealed at various setpoint temperatures. For each chip, the setpoint temperature was maintained for
20 min, followed by controlled cooling at 5 °C min⁻¹ down to room temperature.

The evolution of surface quality for different chips as a function of the reflow temperature is shown
in figure 3. Surface roughness decreases significantly as the annealing temperature approaches 850 °C,
until nearly optical quality is reached. Anisotropy in surface roughness persists after reflow, but becomes
much less pronounced at higher annealing temperatures. Around 850 °C, this anisotropy almost van-
ishes, and the surface roughness R<sub>a</sub> falls below 3 nm in all directions.

It is worth noting that the surface parameters of the samples are strongly modified by reflow,
although the temperature increments are small. Combined with slight variations in chip dimensions
(all cut from the same wafer), this can explain the variability observed in the curves. Nevertheless, the
overall trend is clear: the initially high vertical waviness decreases rapidly, while horizontal waviness is
more affected by the surface reorganization at first (840 °C). Then, as the reflow temperature increases,
roughness along both directions is found to be smaller and more uniform. At higher temperatures (e.g.
above 850 °C), however, surface bowing increases, particularly along the y direction, where the radius
of curvature of the surface can be as small as 60 mm, indicating that a trade-off must be found between
minimizing roughness and preserving surface flatness.

**2.4. Windows transmission characterization**

In addition to the surface characterization of the windows, and in order to evaluate the distortion experi-
enced by a beam passing through the sidewalls, we investigated the beam profiles of a freely propagat-
ing beam through the different reflowed samples, i.e. undergoing propagation through four surfaces. We
used a diode laser emitting at 895 nm (Toptica DL pro), beam-shaped to produce an incident beam of
nearly 460 µm in diameter at the position of the samples. The samples were mounted on a XYZ stage
<figure><img src="image_6.png" /></figure>

with adjustable yaw and pitch. About 80 mm behind the cell, a beam profiler (Newport LBP2), a polar-
imeter (Thorlabs PAX1000IR1) and a power meter (Thorlabs PM100D) are mounted on a rail (perpen-
dicular to the beam) allowing sequential measurements of the beam properties. The results are gathered
in table 1. For each reflowed sample, the optical power was measured in order to determine the trans-
mission of the pair of lateral windows (four surfaces) for an incident vertically linearly polarized beam.
The beam profile was then recorded and, finally, the polarization state of the transmitted beam was
measured (ellipticity angle ϵ) for four different incident polarization states (linear vertical, linear at 45°,
linear horizontal and circular). The ellipticity angle ϵ characterizes the shape of the polarization ellipse
via tan ϵ = *b*/*a*, where *a* and *b* are the semi-major and semi-minor axes, such that ϵ = 0° corresponds
to linear polarization and ϵ = ±45° to circular polarization. Table 1 reports the change in ellipticity
(deterioration) relative to the initial linear (ϵ = 0°) and circular (ϵ = 45°) incident states.

For reflow temperatures of 840 °C and 845 °C, the beam distortion is significant, especially along
the y axis, where a higher waviness had previously been measured. The transmission is also affected by
the surface quality, with losses as high as 14.7% and 10.8%, respectively. At 850 °C, the temperature
<table><caption>**Table 1.** Optical characterization of windows as a function of reflow temperature.</caption><thead><tr><th></th><th>840</th><th>845</th><th>850</th><th>855</th></tr></thead><tbody><tr><td>Reflow temperature (°C)</td><td>840</td><td>845</td><td>850</td><td>855</td></tr><tr><td>Transmission (%)</td><td>71.8</td><td>74.8</td><td>81.6</td><td>76.6</td></tr><tr><td>Power loss (%)</td><td>14.7</td><td>10.8</td><td>4.9</td><td>9.9</td></tr><tr><td>Beam profile*</td><td></td><td></td><td></td><td></td></tr><tr><td>Polarization ellipticity deterioration (°)</td><td>1.0<br>3.6<br>0.2<br>2.9</td><td>0.2<br>2.4<br>0.3<br>1.7</td><td>0.3<br>2.9<br>0.6<br>2.1</td><td>0.1<br>3.8<br>0.4<br>3.6</td></tr></tbody></table>

ultimately retained for further cell fabrication, the distortion decreases and the transmission improves, with losses reduced to 4.9%. At 850 °C, a residual anisotropy of the beam is visible, but it remains smaller than at 855 °C, where the bowing starts to stretch the beam and likely induces some clipping that could account for the reduced transmission. These observations are consistent with the optical profilometry measurements, which showed increased waviness and bowing at lower and higher reflow temperatures, respectively. Regarding the polarization state, it is well preserved, particularly for temperatures between 845 °C and 850 °C, where the ellipticity deterioration remains below 3°, even for an incident circular polarization.

## 2.5. Cells functionalized for magnetometry

Once a Si-glass-Si stack was thermally reflowed at the wafer level, it was assembled with the bottom glass lid and loaded with Cs dispensers. The top glass lid was then anodically bonded to seal the cell under an atmosphere of 760 Torr of nitrogen at 350 °C. As expected, the subsequent laser activation of the dispenser consumes a portion of the nitrogen [4]. Indeed, whereas a pressure of nearly 380 Torr could be expected without dispenser, the nitrogen pressure, determined by measuring the induced frequency shift, is found to be 330 Torr at 95 °C. At this temperature, the nitrogen atmosphere induces a collisional broadening around 5 GHz adding to the 400 MHz Doppler broadened lines. The wafer right after saw dicing is shown on the figure 4(a). This step produces rough external sidewalls, except at the recessed windows, as illustrated in figure 4(b).

The same measurements as in section 2.4 were performed on a cell. The transmission measured through the largest window (corresponding to configuration A in figure 5) is 86.6%, in very good agreement with the expected value $T = 86.53\%$ at normal incidence, obtained by considering Fresnel reflections at the four surfaces (refractive index $n = 1.4645$). Small additional losses are observed along the two lateral axes (3.4% and 1.8%, respectively) but these confirm that the residual roughness and waviness do not lead to strong scattering. The beam profiles show a slight distortion even through the lids (configuration A), which we attribute to a weak etalon effect between the two windows. However, in this case, the polarization state is not measurably affected, regardless of the incident polarization. Along the two lateral windows, the beams are slightly distorted, similarly to the pattern obtained for the sample reflowed at 850 °C. Owing to the surface geometry, linear polarizations are well preserved, whereas a modest deterioration of the ellipticity (between 5° and 10°) is experienced for 45° linear and circular input states. It is worth noting that samples reflowed at 850 °C in chip form exhibit very similar beam patterns to those observed with the cells, although the latter were reflowed at the wafer level. Moreover, we underline that the thermal reflow, although performed at a relatively high temperature, does not appear to affect the bonding. Indeed, several cells have been monitored by linear absorption for weeks after activation, and no significant changes in their absorption spectra have been observed.

<footnote>* The beam profile on the left shows the probing beam with no cell/sample on the optical path.</footnote>
<figure><img src="image_7.png" /><figcaption>**Figure 4.** (a) Wafer after saw dicing. (b) Cell lateral side and window.</figcaption></figure>

### 3. Magnetometry measurements

To evidence the cell potential, a zero-field resonance (ZFR) magnetometer is implemented using one of the fabricated multi-axes cell filled with nitrogen. In this setup, two distributed Bragg reflector lasers are used to generate the pump and probe beams along the *z* and *x*-axis respectively. The pump beam is tuned to the ¹³³Cs *D*₁ line (895 nm) and the probe beam is slightly detuned from the ¹³³Cs *D*₂ line (852 nm), both lasers are free-running. The cell is placed in a three-layer magnetic shield, and the magnetic field is established using a set of three coils. Measurements are carried out by measuring the change in absorption of the transmitted pump light or the polarization state rotation of the transmitted probe light. The pump beam is collimated and passes through a half-wave plate followed by a quarter-wave plate to produce circular polarization. The probe beam is linearly polarized and its amplitude is adjusted using a half-wave plate and a first polarizing beam-splitter (PBS). After passing through the cell, the probe beam is split by a second PBS into two orthogonally polarized components, which are directed onto a differential photodiode. The intensity difference measured between these two beams provides a signal proportional to the polarization rotation.

The light intensities are estimated by measuring the optical power transmitted through the cold cell and considering the window size. The cell temperature and laser intensities are tuned manually in order to optimize sensitivity. To evaluate the magnetometer sensitivity, the noise spectrum is calibrated by generating oscillating magnetic fields of known amplitude at several frequencies between 10 and 100 Hz. The measurement is taken from either the lock-in amplifier output (for the one-beam configuration) or the differential photodiode output (for the two-beam configuration).

Magnetometry measurements are carried out using two different setups, shown in figures 5(a) and (b). The first setup, based on a single-beam geometry, relies on absorption detection whereas the two-beam geometry detects the polarization rotation of the probe beam. By scanning the magnetic field around zero along the *y*-axis, a ZFR is observed (figure 5(c)). For the measurements performed with a single beam, the magnetic field along the *y*-axis is modulated and the dispersive signal is obtained by demodulating the photodiode signal with a lock-in amplifier. To compare the response along different cell axes, absorption measurements are performed in two configurations: either with the pump light passing through the glass lids (configuration A) or through the lateral windows (configuration B). In configuration A, the pump light intensity is 1.6 mW cm⁻² and the cell is operated at a temperature of 120 °C. In configuration B, the pump light intensity is 14 mW cm⁻² and the cell is operated at 150 °C. In the two-beam configuration (C), the magnetometer signal is obtained from polarization rotation of the probe beam. The pump light illuminates the vapor through the lateral windows with an intensity of 14 mW cm⁻² while the probe light uses the main windows with an intensity of 12.6 mW cm⁻². In this configuration, the cell is operated at a temperature of 155 °C. The power spectral density (PSD) of the magnetometer signal for each configuration is shown in figure 5(d). In configuration A, the sensitivity noise floor reaches 100 fT√Hz⁻¹ while in configurations B and C it reaches 200 fT√Hz⁻¹.
<figure><img src="image_8.png" /><figcaption>**Figure 5.** Experimental setup of the zero-field resonance (ZFR) magnetometer for measurements: (a) in absorption and (b) in polarization rotation. (c) Zero-field resonance signal measured in transmission by scanning the magnetic field $B_0$ (config. B). The orange line indicates a Lorentzian fit with a full-width at half-maximum of 22 nT at 155 °C with a 12 mW cm⁻² laser intensity. (d) PSD (power spectral density) of the magnetometer signal for the different configurations. The dotted lines indicate 100 fT√Hz⁻¹ and 200 fT√Hz⁻¹.</figcaption></figure>

## 4. Discussion and conclusion

A part of the sensitivity difference between the configurations can be attributed to the smaller illuminated atomic volume (resulting from the reduced dimensions of the lateral windows), differences in the experimental conditions (temperature, laser intensity, lock-in parameters) and the slightly lower optical quality of the lateral window. In addition, diffraction at the edges of the lateral window, combined with its slightly lower flatness (see section 2.4), slightly alter the polarization state. Increasing the dimensions of the lateral window and/or better shaping the probe beam could therefore enable sensitivities in configurations B and C comparable to those achieved in configuration A. Furthermore, the buffer gas pressure is currently limited by the maximum pressure the bonding machine can withstand, but increasing this pressure could likely improve sensitivity. An alternative approach could be to fill the cell externally [17], eliminating the need for internal dispensers while allowing higher buffer gas pressures.

Compared to prior approaches [24], our method offers significant advantages. By employing LAE rather than direct laser ablation, we achieve an intrinsically lower level of roughness on the lateral glass windows. This eliminates the need for a mold to emboss the glass surface since a simple thermal reflow improves the surface roughness to $R_a < 3$ nm. Consequently, issues related to alignment, mold wear, and dimensional accuracy are avoided, enabling simpler and more reliable mass production while improving consistency across large-scale manufacturing. Moreover, the introduction of auxiliary cavities ensures that the saw blade never comes in contact with the windows, thereby eliminating the need for an additional polishing step. Despite the limited buffer gas pressure of 330 Torr, the fabricated cells achieved sensitivities of 100 fT√Hz⁻¹ with optical access through the main window and 200 fT√Hz⁻¹ through the lateral windows.
## Data availability statement

All data that support the findings of this study are included within the article (and any supplementary files).

## Acknowledgments

This work was supported by the Direction Générale de l'Armement (DGA) and by the Agence Nationale de la Recherche (ANR) in the frame of the ASTRID project named NOMAD (Grant ANR-23-ASTR-0020) and EIPHI Graduate school (Grant ANR-17-EURE-0002). The PhD thesis of L Péroux is co-funded by Agence Innovation Defense (AID) and Région Hauts-de-France. The PhD thesis of A Dewilde is funded by the ANR (Grant ANR-23-CE42-0012). This research work has been partially undertaken with the support of IEMN and FEMTO-ST microfabrication facilities (CMNF and MIMENTO), both part of the French Renatech network. We gratefully acknowledge L. Furfaro and J-M. Merolla for lending us the annealing furnace used in this work.

## Author contributions

L Péroux ID 0009-0006-9838-2677

Data curation (lead), Formal analysis (equal), Investigation (lead), Validation (lead), Visualization (lead), Writing – original draft (lead), Writing – review & editing (equal)

A Dewilde ID 0009-0008-7727-8170

Data curation (supporting), Formal analysis (supporting), Investigation (equal), Writing – original draft (supporting)

A Mursa

Investigation (supporting), Methodology (lead), Resources (supporting), Writing – review & editing (supporting)

A Mazzamurro

Investigation (supporting), Resources (supporting), Writing – review & editing (supporting)

J Bonhomme ID 0000-0002-5776-4170

Investigation (supporting), Writing – review & editing (supporting)

Q Tanguy

Investigation (supporting), Methodology (supporting), Resources (supporting), Writing – review & editing (supporting)

E Klinger ID 0000-0001-7461-9568

Data curation (equal), Formal analysis (equal), Validation (equal), Writing – review & editing (supporting)

L Gauthier-Manuel

Resources (supporting)

O Gaiffe

Data curation (supporting), Formal analysis (equal), Validation (equal), Visualization (supporting), Writing – review & editing (supporting)

A Talbi

Funding acquisition (supporting), Resources (supporting)

R Boudot

Funding acquisition (supporting), Resources (supporting), Writing – review & editing (supporting)

P Pernod

Funding acquisition (equal), Project administration (lead), Supervision (equal)

J-F Clément

Resources (supporting)
V Maurice D 0000-0003-3559-4120

Conceptualization (supporting), Data curation (equal), Formal analysis (equal), Funding acquisition (equal), Investigation (equal), Methodology (equal), Project administration (equal), Supervision (equal), Validation (equal), Visualization (supporting), Writing – original draft (supporting), Writing – review & editing (equal)

N Passilly D 0000-0002-4447-4588

Conceptualization (lead), Data curation (equal), Formal analysis (equal), Funding acquisition (equal),
Investigation (equal), Methodology (equal), Project administration (equal), Supervision (equal),
Validation (equal), Visualization (equal), Writing – original draft (equal), Writing – review &
editing (equal)

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