Subscriber access provided by TULANE UNIVERSITY
A: New Tools and Methods in Experiment and Theory
Absolute Nonlinear Refractive Index Spectra Determination of Organic Molecules in Solutions Marlon dos Santos Melhado, Emerson Cristiano Barbano, Marcelo Gonçalves Vivas, Sérgio Carlos Zilio, and Lino Misoguti J. Phys. Chem. A, Just Accepted Manuscript • DOI: 10.1021/acs.jpca.8b10984 • Publication Date (Web): 04 Jan 2019 Downloaded from http://pubs.acs.org on January 9, 2019
Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.
is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.
Page 1 of 20 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
The Journal of Physical Chemistry
Absolute
Nonlinear
Refractive
Index
Spectra
Determination of Organic Molecules in Solutions Marlon dos Santos Melhado, † Emerson Cristiano Barbano, ‡ Marcelo Gonçalves Vivas, * Sérgio Carlos Zilio, †,§ and Lino Misoguti † †
Instituto de Física de São Carlos, Universidade de São Paulo, CP 369, 13560-970 São Carlos, SP, Brazil
‡Departamento *Laboratório
§Instituto
de Física, Universidade Federal do Paraná, CP 19044, 81531-980 Curitiba, PR, Brazil
de Espectroscopia Óptica e Fotônica, Universidade Federal de Alfenas, Poços de Caldas, MG, Brazil
de Física, Universidade Federal de Goiás, 74001-970, Goiânia, GO, Brazil
E-mail:
[email protected] ABSTRACT: It has been a great challenge to measure the spectrum of pure boundelectronic third-order nonlinear refraction (n2) of organic chromophores in solutions because of the spurious contribution from the solvent and cuvette walls. In order to circumvent this problem, we present here a new method to obtain highly accurate absolute n2 value of organic molecules in solutions with a self-referenced nonlinear ellipse rotation (NER) technique. As a proof of concept, we measured n2 spectra of two well-know chromophores, rhodamines B and 6G dissolved in methanol, in the range from ~600 to 1200 nm. Our results pointed out that these two dyes present similar dispersion curves with strong negative nonlinearities near the one-photon absorption band and small positive values at long wavelengths. Furthermore, the negative signal of the dyes can be strong enough to cancel and even invert the positive nonlinear refraction of the solvent (methanol) as the solution’s concentration increases. To understand the n2 spectrum and its connection to molecular properties of organic chromophores, we employed the sum-over-states (SOS) approach within the few-energy-level model and observed an excellent agreement between the experimental and theoretical spectra. In this way, we believe that employing our NER technique and the SOS model, it is possible to determine both experimentally and theoretically the absolute magnitude and spectra of pure electronic n2 for a large variety of other organic molecules.
1 ACS Paragon Plus Environment
The Journal of Physical Chemistry 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Page 2 of 20
1. Introduction The advent of reliable optical parametric amplifier (OPA) systems delivering tunable laser pulses paved the way for nonlinear absorption (NLA) and refraction (NLR) measurements of materials in a broad spectral range. 1 These third-order nonlinear optical phenomena are the key to the development of organic photonics applications like optical power limiting,
2-3
all-optical switching,
4-5
high resolution microscopy,
6-7
photodynamic
therapy, 8-9 white-light continuum generation 10-11 and so on. To date, NLA measurements such as two-photon absorption (2PA:2) spectra of organic molecules are much more common than pure bound-electronic NLR (n2),
12-13
mainly because 2 is simpler to
measure than n2. For example, absolute NLR and NLA can be both measured by the Z-scan method,
14
but the open aperture configuration used in NLA allows the collection of all
light, thus providing a much better signal-to-noise ratio and less sensitivity to sample’s imperfections (scratch, non-parallelism, scattering, etc.). In addition, NLA results are easier to be achieved because solvent molecules do not present considerable 2PA cross section values (2
