#
APS April Meeting 2021

## Volume 66, Number 5

##
Saturday–Tuesday, April 17–20, 2021;
Virtual; Time Zone: Central Daylight Time, USA

### Session T08: Advanced Acceleration, Lasers & Diagnostics

3:45 PM–5:21 PM,
Monday, April 19, 2021

Sponsoring
Unit:
DPB

Chair: Sergei Nagaitsev, Fermilab

### Abstract: T08.00007 : UV Laser Pulse Trains for Raman Spectroscopy.*

4:57 PM–5:09 PM
Live

Preview Abstract
Abstract

####
Authors:

Dustin Swanson

(University of Maryland, College Park)

Phillip Sprangle

(University of Maryland, College Park)

The theoretical framework for Raman spectroscopy using a UV probe laser
pulse train consisting of multi femtosecond pulses is developed. We show
selective excitation of a single Raman mode by tuning the pulse parameters.
The use of UV radiation for the probe has a number of advantages for this
application. The pulse train consists of multiple pulses of the form, $I_{1}
(\tau )=I_{0} \sin^{2}(\pi \tau /\tau_{L} )\left( {\Theta \left( \tau
\right)-\Theta \left( {\tau -\tau_{L} } \right)} \right)$, where $\tau_{L}
$ is the duration of a single pulse, $\tau_{FWHM} ={\tau_{L} }
\mathord{\left/ {\vphantom {{\tau_{L} } 2}} \right.
\kern-\nulldelimiterspace} 2,\mbox{\thinspace \thinspace }I_{0} =n_{0}
c\varepsilon_{0} {E_{peak}^{2} } \mathord{\left/ {\vphantom {{E_{peak}^{2}
} 2}} \right. \kern-\nulldelimiterspace} 2$, is the peak intensity and
$\Theta \left( \tau \right)$ is the Heaviside function. The analysis is
performed in the group velocity frame, where $\tau =t-z/\mbox{v}_{G}
\,\,\mbox{and}\,\,\eta =z$. The reduced propagation equation for the probe
pulse field is ${\partial E_{P} (\eta ,\tau )} \mathord{\left/ {\vphantom
{{\partial E_{P} (\eta ,\tau )} {\partial \eta }}} \right.
\kern-\nulldelimiterspace} {\partial \eta }=i(\mu_{0} \omega_{0}^{2}
/2k_{0} )P_{NL} (\eta ,\tau )$ where $P_{NL} $ is the non-linear
polarization field. The probe intensity is modulated and grows approximately
linearly with the interaction distance. We simulate the detection of the
COVID-19 pathogen with a laser pulse train consisting of 10 micro-pulses,
each with a duration of $\approx $ 32 fs, peak intensity of
10$^{\mathrm{10\thinspace }}$W/cm$^{\mathrm{2}}$ and central wavelength of
250 nm (frequency tripled Ti:Sapphire). The micro-pulse duration is chosen
to match the vibrational period of the smallest Raman shift resonance of the
pathogen, $\omega_{V} /(2\pi c)=1032\mbox{cm}^{\mbox{-1}}$. This simulation
showed the selective excitation of a single Raman mode.

*The authors would like to acknowledge the ONR and the PM Quentin Saulter for proposing this problem.