We observed experimentally intense scattered lights with multicolors at the surface of microbubbles formed by a focused femtosecond laser inside the water. This optical scattering phenomenon is found, to the best of our knowledge, for the first time since the invention of the femtosecond laser.

1. Introduction
We observed experimentally intense scattered lights with multicolors at the
surface of microbubbles formed by a focused femtosecond laser inside the water.
This optical scattering phenomenon is found, to the best of our knowledge, for the
first time since the invention of the femtosecond laser. However, it is well known
that, after focusing femtosecond laser inside water firstly it shows optical
breakdown because of photoionization effect [1], then, loose geometrical focusing
condition (because of water) creates plasma strings that is considered as
filamentation inside water which also creates white light generation, blue shifting
phenomena, laser induced bubbles generation by ionocavitation [2], those
bubbles show irradiation, nucleation, growth, growth, rebound, etc. [3]. And we
observed our new found multicolour optical scattering from the surface of those
bubbles.
Methods And Experimental Setup
Observational Results
The focused femtosecond laser region under water is very dynamic and also it is
challenging in terms of observation, there are so many mechanisms are involved
there, but we focused into some specific topics where our Observation can be
summarized as below :
Explanation
References
1. Zysset, B., Fujimoto, J. G., & Deutsch, T. F. Applied Physics B, 48(2), 139-147 (189).
2. Mizushima, Y., & Saito, T. Applied Physics Letters, 107(11), 114102 (2015).
3. L. Berthe, R. Fabbro, P. Peyre, L. Tollier, and E. Bartnicki, J. Appl. Phys. 82 (6), 2826 (1997).
4. Fengjiang Liu el at. Optics Express, 25(19), 13258 (2016).
5. Hao, Zuoqiang, et al. Optics Express, 19(8), 7799 (2011).
6. Couairon, A., & Mysyrowicz, A. Physics reports, 441(2-4), 47 (2007).
7. Ooi, C. R., & Sanny, A. I. JOSA B, 34(10), 2072 (2017)..
Contact: bigganobish@gmail.com & rooi@um.edu.my
Conclusion
Mauris orci mi, varius id diam, egestas auctor enim.
*Question: Are the Colors Correlated with Space and Bubble Size?
Answer: It has been observed similar size bubbles scattered different colors in different
regions so answer is No.
MULTICOLOR SCATTERING BY TIGHTLY FOCUSED FEMTOSECOND LASER
A. I. Sanny & C. H. Raymond Ooi
Department of Physics, University of Malaya, Kuala Lumpur, Malaysia
• Biconvex Objective Lens : 2.5 cm
• The focused region : 100 μm
Our new found optical phenomena discussed based on observation and our known
fundamental knowledge on nonlinear properties of lights when femtosecond laser
interacts with water [7]. This effect is still a subject to discuss theoretically in details.
Beside fundamental science we think this is also very important for many applications
related to biophysics, biomedical engineering, fabrications of nanoparticles under water,
etc.
In this experimental study, the laser beam, with a diameter of 1 cm, is focused into the
water by a biconvex objective lens from the side of a water container. And camera
and lights are placed such a way that we can observe live dynamic reactions when
laser was focused inside water.
Ti: Sapphire femtosecond laser amplifier System Quantities
• Energy per pulse : 2.5mJ
• Laser Pulse duration : 50 fs
• Central wavelength : 800nm
• Repetition rate : 1KHz
• Average Power : 3.5 W
• Peak Power : 𝟓 𝟏𝟎 𝟏𝟎
W
• Peak intensity: 𝟏𝟎 𝟏𝟒
𝑾𝒄𝒎−𝟐
 Laser induced breakdown in water and self focusing
or filamentation
 White light generation at focused portion, blue
shifting property, Multi-spectral effects
*Multispectral image
taken at the laser axis
1 m away from the
focus after the laser
passes through the
water due to nonlinear
optical interactions for
different average
laser powers. The
bottom panels show
the colourful image at
low power and the
effect of lower
repetition rate of 500
kHz.
 Creation of bubbles, their motions due to pressure
force [4] and in between we have found strong color
light scattering
(a) Scatter plot showing the spatial distributions of the sparkling colors obtained by
analyzing the movie shot-by-shot. (b) Distributions of the bubble diameters for
each color. (c) Overall distribution of bubbles with all colors and a Gaussian fit with
mean 21.8 μm and variance 30 μm.
The physics of the colored filaments was described in ref. [5] as due to the filaments
having different degrees of nonlinearity, self-focusing, SPM, and multiphoton ionization
(plasma defocusing), as well as different laser intensities at different positions, leading
to different degrees of spectral broadening, from our understanding, this phenomena
acts from behind to show colorful sparking from microbubble surface. For peak power
of 8 GW, the number of filaments is estimated to be [6],
(the filaments numbers)
Pin is the average laser power, Pfil is the power carried by each filament and we use n2
= 26×10-21m2W-1
Some statistical data :