With biblatex you can use the field addendum, which is similar to note, but always printed at the end of the bibliography entry:
\documentclass{article}
\usepackage{filecontents}
\begin{filecontents*}{\jobname.bib}
@article{dawlaty,
author={Jahan M. Dawlaty and Yunquing Chen},
title={Measurement of the optical absorption of graphene in the terahertz},
journal={Applied Physics Letters},
year={2008},
addendum={\par
Research Group: Cornell \\
Pump Wavelength: 500 nm. \\
Probe Wavelenth: 7 microns. \\
Relaxation Time: 50 fs.}}
@article{george,
author={Paul George and Dmitry Vekslar},
title={Measurement of Ultrafast Carrier Dynamics in Graphene},
journal={Applied Physics Letters},
year={2009}}
\end{filecontents*}
\usepackage[sorting=none]{biblatex}
\addbibresource{\jobname.bib}
% to remove the addendum (https://tex.stackexchange.com/questions/208441)
% in the case that you want to use the same .bib file elsewhere without them
%\AtEveryBibitem{%
% \clearfield{addendum}%
%}
\begin{document}
\nocite{*}
\printbibliography
\end{document}
For normal BibTeX, you could (ab)use the note field in the bib-file. This only works if the note is typeset last of course, and I don't know if that always is the case. Hence, this may not be a solution at all, though it works for the example you posted.

\documentclass{article}
\usepackage{filecontents}
\begin{filecontents*}{\jobname.bib}
@article{dawlaty,
author={Jahan M. Dawlaty and Yunquing Chen},
title={Measurement of the optical absorption of graphene in the terahertz},
journal={Applied Physics Letters},
year={2008},
note={\par
Research Group: Cornell \\
Pump Wavelength: 500 nm. \\
Probe Wavelenth: 7 microns. \\
Relaxation Time: 50 fs.}}
@article{george,
author={Paul George and Dmitry Vekslar},
title={Measurement of Ultrafast Carrier Dynamics in Graphene},
journal={Applied Physics Letters},
year={2009}}
\end{filecontents*}
\begin{document}
\nocite{*}
\bibliographystyle{plain}
\bibliography{\jobname}
\end{document}
notefield in the bib-file I suppose, putting the extra info there, optionally with some linebreaks etc. – Torbjørn T. Dec 30 '12 at 22:30annotefield, which was designed for producing annotated bibliographies (though it is not used by the standard styles). In general, however, your job will probably be much easier if you usebiblatex. – jon Dec 30 '12 at 23:01