Full length article
Investigation on thermally-induced optical nonlinearity of alcohols
Qian Zhang
a
, Xuemei Cheng
a,
⇑
,BoHe
a
, Zhaoyu Ren
a
, Ying Zhang
b
, Haowei Chen
a,
⇑
,
Jintao Bai
a
a
State Key Lab Incubation Base of Photoelectric Technology and Functional Materials, National Photoelectric Technology, Functional Materials and Application of Science
and Technology International Cooperation Center, Institute of Photonics & Photon-Technology, Northwest University, Xi’an 710069, China
b
School of Science, Engineering University of PAP, Xi’an 710086, China
article info
Article history:
Received 19 June 2017
Received in revised form 24 November 2017
Accepted 9 December 2017
Keywords:
Thermal nonlinear optical effect
Self-phase modulation
Kerr effect
Diffraction pattern
abstract
In this work, we studied the thermally-induced optical nonlinearity of alcohols by analyzing the far-filed
diffraction rings patterns, which are generated when the alcohols are illuminated by a laser beam reso-
nant to their overtones. We deduced the nonlinear refractive index coefficient n
2
generated by thermal
nonlinear optical effect to be ð20:53 00:03Þ10
8
cm
2
=W, which is much higher than that of Kerr
effect (7:7 10
16
cm
2
=W). The results also demonstrated that the thermally-induced optical nonlinear-
ity increased with the laser power and sample concentration increasing. The notable nonlinearity sug-
gests that thermal effect has potentials in many applications such as optical spatial modulation, and
trapping and guiding of atoms.
Ó 2017 Elsevier Ltd. All rights reserved.
1. Introduction
A number of nonlinear optical phenomena occur due to the
light intensity dependent nonlinear refraction index. Taking
advantages of those phenomena, people have developed many
novel applications, such as all-optical modulation [1,2], optical
switching [3–6], optical limiting [7–9], optical delays [10,11].In
mostly reported cases, nonlinear refraction indexes are obtained
based on the optical Kerr effect. In fact, thermal nonlinear optical
effect can also generate intensity dependent nonlinear refraction
index [12–15]. Because it has similar properties as Kerr effect, it
is also named as ‘‘Kerr-like effect” [16]. The principle of the thermal
nonlinear optical effect is that: when the laser beam passes
through a medium, the medium is heated and a temperature gra-
dient is formed at the local area, which would result in thermal
expansion. Then the acoustic wave propagating in a medium
changes the density distribution of the medium, which finally
changes the refractive index. As the temperature gradient is closely
related to the light intensity, the thermally-induced refractive
index is light intensity dependent. Thermal nonlinearities are com-
monly larger than the electronic nonlinearities of the same mate-
rial by several orders of magnitude [17]. Nevertheless, there are
relatively fewer researches.
In this work, we report the observation of far-field diffraction
rings pattern of O-H bond based on thermal nonlinear optical
effect. Experimentally, we take ethanol, methanol, propanol and
butanol as the nonlinear mediums and obtain the far-field diffrac-
tion rings patterns around the overtone region of the vibration of
OAH bond at the range from 720 nm to 830 nm. The characteristics
of far-field diffraction rings patterns regarding to the laser power,
the concentration and position of sample are demonstrated. To
illustrate the results, thermal nonlinear optical effect is considered
theoretically. Finally, the nonlinear refractive indexes are approxi-
mated by the number of the diffraction rings, which are further
confirmed by the z-scan method. The notable nonlinearity (8
orders higher than Kerr effect) suggests that thermal nonlinear
optical effect has potentials in many applications. For example,
people can achieve a continuous lateral phase modulation of inci-
dent light by changing the laser power, the concentration and the
position of sample [18]. Such a phase modulation method is of par-
ticular advantage for the intense laser beam because of the high
damage threshold. Moreover, hollow laser beam of tunable size
can be obtained, which is of particular importance in trapping
the particles of various sizes [19].
2. Experiment
A Gaussian beam is obtained from a tunable Titanium sapphire
laser (Spectra-Physics, Matisse TR, CW, tunable from 740–850 nm)
and focused into nonlinear medium by a lens with a focal length of
200 mm. The radius of laser beam at output is 0.7 mm and the
beam waist at focus is estimated to be 70
l
m or so. The wave-
length of the laser was set at 765 nm during the experiments.
https://doi.org/10.1016/j.optlastec.2017.12.017
0030-3992/Ó 2017 Elsevier Ltd. All rights reserved.
⇑
Corresponding authors.
E-mail addresses: xmcheng@nwu.edu.cn (X. Cheng), chenhaowei2005@126.com
(H. Chen).
Optics and Laser Technology 102 (2018) 140–146
Contents lists available at ScienceDirect
Optics and Laser Technology
journal homepage: www.elsevier.com/locate/optlastec