114106-3
Liew, Moreland, and Gerginov
Appl. Phys. Lett. 90, 114106 ͑2007͒
from the two ground-state components. The microwave fre-
quency was scanned in a 20 kHz interval, and the transmis-
sion through the cell increased when it matched exactly one-
half of the atomic ground-state splitting, creating the
resonance. The CPT linewidth of 2.7 kHz suggests that nar-
row linewidths are possible from azide-derived cesium cells.
For clock applications, temperature compensation could
be obtained by prefilling the anodic bonding chamber with
other buffer gases before cell sealing. Furthermore, this tech-
nique allows for creation of high buffer gas pressure inside
the cell. For magnetometer applications where only the high
buffer gas pressure is desired and temperature compensation
is not as critical, these N buffer gas cells may be sufficient
2
in their present form.
In summary, we have demonstrated thin-film deposition
and photodecomposition of cesium azide for filling micro-
fabricated atomic resonance cells. This method replaces the
technically complex and limiting process of handling liquid
cesium with a remote and wafer-level in situ production of
the cesium. This method also combines the formally dispar-
ate functions of cell fabrication and cell filling into one
seamless procedure that is readily amenable to massively
parallel processing, a feature which may be critical to future
commercialization of CSADs. Furthermore, these cells are
devoid of noncesium chemical residues that might react over
time with the cesium; thus the cells remain chemically pure
and the cell windows optically clear. Finally, this technique
allows for a careful control of the final buffer gas pressure
through varying the film deposition and photolysis
parameters.
FIG. 3. ͑Color online͒ ͑a͒ Photograph of a cell, viewed through the glass
window, showing the cesium produced in situ from azide photodecomposi-
tion. Most cells contain less azide than shown in this figure. Here a cell with
more unreacted azide is shown for clarity. ͑b͒ Cesium optical absorption
spectrum obtained from a cell in which a film of CsN3 was deposited and
photodissociated. The N2 buffer gas pressure is estimated from the line
broadening to be about 350 Torr at room temperature.
which in our experiments range from 27 kPa to over 270 kPa
͑
about 200–2000 Torr͒, may be obtained. The cells are more
This work was supported by the U.S. Defense Advanced
Research Projects Agency’s Microsystems Technology Of-
fice. The authors thank Svenja Knappe, Ying-Ju Wang, and
John Kitching at NIST for valuable technical discussions,
and Daniel Porpora at NIST for assistance with thermal
evaporator construction. This work is a contribution of the
National Institute of Standards and Technology and is not
subject to U.S. copyright.
optically transparent than in our previous work because they
contain no bulk oxides or residues except for a thin film of
unreacted azide. Furthermore, cells have been made which
show no noticeable change in the optical absorption line-
width or contrast after one year. This suggests that the
chemical environment within the cell is stable, which is im-
portant for the functioning of atomic-based instruments.
Figure 4 shows a cesium coherent population trapping
1
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FIG. 4. ͑Color online͒ CPT transmission for a CsN -derived cell. The N
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