Does anyone know how I can get this symbol in LaTeX?

Question

I found it in my differential equations book but I can't seem to get it to work. The only things that look close are \mathscr{L} and \mathcal{L}.

Answer 1

Not quite the same, but dutchcal has a comparatively close glyph:

        \documentclass[12pt]{article}
        \usepackage[utf8]{inputenc}

        \usepackage{dutchcal}

        \begin{document}%
        $ \begin{array}[t]{c@{\quad}c}
         \small \verb+ \mathcal + & \small\verb+ \mathbcal + \\[6pt]
             \mathcal{L} & \mathbcal{L}
            \end{array} $

        \end{document} 

Answer 2

The calligraphic/script math glyphs are intended to appear handwritten, so there is a lot of variation between fonts, just like with handwriting in real life.

To add to the other answers and comments:

In Unicode, Laplace transform is in the Letterlike block (at U+2112) and the bold script capital L version is in the Mathematical Alphanumeric Symbols block (at U+1D4DB), so using unicode-math package and system fonts, a sampling of system math fonts looks like this:

MWE

\documentclass[12pt,varwidth,border=6pt]{standalone}
\usepackage{xcolor}
\pagecolor{red!3}
\usepackage{unicode-math}
%\usepackage{accents}
\setmathfont{XITS Math}[Colour=blue]
%\setmathfontface\mxits{XITS Math}
\setmathfontface\masana{Asana Math}
\setmathfontface\mdejavu{DejaVu Math}
\setmathfontface\mtgdeja{TeX Gyre DejaVu Math}
\setmathfontface\mpagella{TeX Gyre Pagella Math}
\setmathfontface\mbonum{TeX Gyre Bonum Math}
\setmathfontface\mschola{TeX Gyre Schola Math}
\setmathfontface\mtermes{TeX Gyre Termes Math}
\setmathfontface\mlatin{Latin Modern Math}
\setmathfontface\mcambria{Cambria Math}
\setmathfontface\mfira{Fira Math}
\setmathfontface\mfreeserif{FreeSerif}
\setmathfontface\mlibert{Libertinus Math}
\setmathfontface\mnoto{Noto Sans Symbols}
\setmathfontface\mqui{Quivira}
\setmathfontface\mstixtwo{STIX Two Math}
\setmathfontface\mstixgen{STIXGeneral}
\setmathfontface\msymbola{Symbola}
\setmathfontface\mgaramond{\detokenize{Garamond-Math}}
\newcommand\mfsize{\Huge}
\setmainfont{Noto Serif}


\newcommand\themassym{ℒ}%
\begin{document}
\section*{Sampling {\mfsize $\themassym $}}

\vspace{24pt}


\begin{tabular}{rccl}
XITS Math & \mfsize $\themassym$ & \mfsize $\mcambria \themassym$ & Cambria Math \\ 
\ &\ & \ & \ \\ 
Asana Math & \mfsize $\masana {\themassym}$ & \mfsize $\mfira \themassym$ & Fira Math \\ 
\ &\ & \ & \ \\ 
DejaVu Math & \mfsize $\mdejavu \themassym$ & \mfsize $\mfreeserif \themassym$ & FreeSerif \\
\ &\ & \ & \ \\ 
Tex Gyre Bonum Math & \mfsize $\mbonum \themassym$ & \mfsize $\mlibert \themassym$ & Libertinus Math \\
\ &\ & \ & \ \\ 
Tex Gyre DejaVu Math & \mfsize $\mtgdeja \themassym$ & \mfsize $\mnoto \themassym$ & Noto Sans Symbols \\
\ &\ & \ & \ \\ 
Tex Gyre Pagella Math & \mfsize $\mpagella \themassym$ & \mfsize $\mqui \themassym$ & Quivira \\
\ &\ & \ & \ \\ 
Tex Gyre Schola Math & \mfsize $\mschola \themassym$ & \mfsize $\mstixtwo \themassym$ &STIX Two Math \\
\ &\ & \ & \ \\ 
Tex Gyre Termes Math & \mfsize $\mtermes \themassym$ & \mfsize $\mgaramond \themassym$ & Garamond-Math \\
\ &\ & \ & \ \\ 
Latin Modern Math & \mfsize $\mlatin \themassym$ & \mfsize $\msymbola \themassym$ & Symbola \\
\end{tabular}


\end{document}