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\fancyhead[C]{{\footnotesize \textit{HRMS, 28th Colloquium, Dijon, France, Aug. 28 - Sept. 1, 2023}}}
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\title{SUB-DOPPLER SPECTROSCOPY OF $\bf C_2H_2$ BY \uline{N}OISE-\uline{I}MMUNE
\uline{C}AVITY-\uline{E}NHANCED \uline{O}PTICAL \uline{H}ETERODYNE
\uline{M}OLECULAR \uline{S}PECTROSCOPY AROUND 1.4 $\upmu$m}

\author{\underline{\FirstName PATRICK \LastName DUPR\'E}}
\address{Laboratoire Interdisciplinaire Carnot de Bourgogne, 9 Avenue Alain Savary, BP 47870, 21078 Dijon Cedex, France}

\category {3}
\begin{document}

\maketitle

An insight of sub-Doppler high-resolution lines of ${\rm C_{2}H_{2}}$
in the Near-Infrared will be presented. Data have been obtained by
using the very sensitive Noise-Immune Cavity-Enhanced Optical Heterodyne
Molecular Spectroscopy (NICE-OHMS) technique. Combined with a Wavelength
Modulation, this technique is theoretically optimum to measure weak
absorption transitions at a very high accuracy when it is associated
with an Optical Frequency Comb (OFC). Nevertheless, under saturation
conditions (Lamb-dip), a full control of the experimental parameters
is demanded. Indeed, lacks of control may be at the origin of data
misinterpretation. Here, we anticipated to use ${\rm C_{2}H_{2}}$
as a benchmarking system for the NICE-OHMS technique.

Preliminary results will be presented. They are typically based on
the mastering of the two key parameters which are the sample pressure,
and the impinging power of the electromagnetic field.

In the past, data obtained under saturated absorption conditions have
demonstrated that the resonance profiles may be difficult to interpret.
Indeed, a genuine data analysis cannot be obtained without an appropriate
modeling that can be a source of difficulties when dealing with nonlinear
spectroscopy. Actually, several sets of data obtained with different
setups, and by different authors do not allow converging toward a
universal/unique model. For example, the role of the Velocity Changing
Collision at low pressure can be challenged.

We anticipate that such kind on analysis, associated with a relevant
model can help studying the different collisional processes inherent
to any bulk system, typically a low pressure.

Nonlinear behaviors, resonance shape, pressure broadening, pressure
frequency shift and resonance amplitude/integral will be mainly discussed
in the perspective of quantitative analyses.
\end{document}
