skip to main content
US FlagAn official website of the United States government
dot gov icon
Official websites use .gov
A .gov website belongs to an official government organization in the United States.
https lock icon
Secure .gov websites use HTTPS
A lock ( lock ) or https:// means you've safely connected to the .gov website. Share sensitive information only on official, secure websites.

Explore Research Products in the PAR
It may take a few hours for recently added research products to appear in PAR search results.


  • NSF Public Access
  • Search Results
  • Photoacoustic identification of laser-induced microbubbles as light scattering centers for optical limiting in a liquid suspension of graphene nanosheets
Title: Photoacoustic identification of laser-induced microbubbles as light scattering centers for optical limiting in a liquid suspension of graphene nanosheets
Liquid suspensions of carbon nanotubes, graphene and transition metal dichalcogenides have exhibited excellent performance in optical limiting. However, the underlying mechanism has remained elusive and is generally ascribed to their superior nonlinear optical properties such as nonlinear absorption or nonlinear scattering. Using graphene as an example, we show that photo-thermal microbubbles are responsible for optical limiting as strong light scattering centers: graphene sheets absorb incident light and become heated up above the boiling point of water, resulting in vapor and microbubble generation. This conclusion is based on the direct observation of bubbles above the laser beam as well as a strong correlation between laser-induced ultrasound and optical limiting. In situ Raman scattering of graphene further confirms that the temperature of graphene under laser pulses rises above the boiling point of water but still remains too low to vaporize graphene and create graphene plasma bubbles. Photo-thermal bubble scattering is not a nonlinear optical process and requires very low laser intensity. This understanding helps us to design more efficient optical limiting materials and understand the intrinsic nonlinear optical properties of nanomaterials.  more » « less
Award ID(s):
1809622
PAR ID:
10171974
Author(s) / Creator(s):
; ; ; ; ; ; ; ; ; ; ;
Date Published:
Journal Name:
Nanoscale
Volume:
12
Issue:
13
ISSN:
2040-3364
Page Range / eLocation ID:
7109 to 7115
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. ; ; ; ; (, Advanced Optical Materials)
    Abstract Titanium nitride nanoparticles have become a research interest due to their distinguished optical and photothermal properties. Furthermore, the search for nanoparticle solutions with tunable nonlinear optical properties for laser‐based applications is critical. More specifically, third order optical nonlinearities such as reverse saturable absorption, optical liming, and self‐focusing are important in the biomedical and electronics fields. The optical nonlinearities of titanium nitride plasmonic nanoparticles are investigated as a function of material concentration in water solutions. Furthermore, the effect of nanoparticle clustering on optical nonlinearities is investigated by fabricating micrometer‐sized clusters of ≈50 nm titanium nitride particles. These studies demonstrate that the nonlinear absorption coefficient increases linearly with concentration. However, clusters require higher concentrations compared to the freestanding nanoparticles to exhibit similar nonlinear absorption coefficient and optical density. Similarly, the optical limiting threshold for titanium nitride nanoparticles appears to be lower compared to the cluster solutions, which is impacted by the collective scattering of nanoparticles and high reverse saturable absorption. In addition, self‐focusing is observed in the continuous resonant regime. This study provides an in‐depth analysis of the nonlinear optical properties of titanium nitride, with relevant consequences for applications such as sensor protection and photothermal therapy. 
    more » « less
  2. ; ; ; ; ; ; ; ; ; ; et al (, Journal of Physics: Conference Series)
    Abstract We have investigated crystalline AlGaAs/GaAs optical coatings with three ultra-stable cavities operating at 4 K, 16 K, 124 K and 297 K. The response of the cavities’ resonance frequencies to variations in optical power indicates non-thermal effects beyond the photo-thermo-optic effect observed in dielectric coatings. These effects are strongly dependent on the intensity of the intracavity light at 1.5 μm. When the rear side of the mirrors is illuminated with external light, we observe a prominent photo-modified birefringence for photon energies above the GaAs bandgap, which points to a possible mechanism relating our observations to the semiconductor properties of the coatings. Separately, we also present a low maintenance evolution of our 124 K silicon cavity system where the liquid nitrogen based cooling system is replaced with closed cycle cooling from a pulse-tube cryo-cooler. 
    more » « less
  3. ; ; ; ; ; (, Catalysis Today)
    Khatib, Sheima J; Groppo, Elena (Ed.)
    The CO2 hydrogenation (HYD) reaction was investigated over Ni phosphide (Ni3P, Ni12P5, Ni2P) catalysts to probe the effect of the NixPy phase on photo-thermal catalytic properties in comparison to Ni metal. The light absorption properties of 2.5 wt% NixPy/SiO2 catalysts differ substantially, with the extent of light absorption decreasing as the P/Ni molar ratio of the Ni phosphide phase increases. This finding directly impacts the photo-thermal catalytic properties as the photo-enhancement (light activity / dark activity) correlates linearly with the extent of light absorption. For comparison purposes, 2.5 wt% Ni/SiO2 catalysts were also investigated and showed high activity but suffered from low CO selectivity (57-68%). A Ni3P/SiO2 catalyst was the most active of the Ni phosphides with high CO selectivity (>95%), while Ni12P5/SiO2 and Ni2P/SiO2 catalysts had lower CO2 HYD activities but CO selectivities above 98%. Upon light exposure, the NixPy/SiO2 (and Ni/SiO2) catalysts exhibited significant rises of temperature (~200 K increase from room temperature), indicating the importance of photothermal heating in increasing the CO2 HYD rate. The findings highlight how a non-metal element (i.e., P) plays a crucial role in tailoring the photo-thermal catalytic properties of earth abundant nickel metal. 
    more » « less
  4. ; ; (, Nature Nanotechnology)
    Optical tweezers have emerged as a powerful tool for the non-invasive trapping and manipulation of colloidal particles and biological cells1,2. However, the diffraction limit precludes the low-power trapping of nanometre-scale objects. Substantially increasing the laser power can provide enough trapping potential depth to trap nanoscale objects. Unfortunately, the substantial optical intensity required causes photo-toxicity and thermal stress in the trapped biological specimens3. Low-power near-field nano-optical tweezers comprising plasmonic nanoantennas and photonic crystal cavities have been explored for stable nanoscale object trapping4,5,6,7,8,9,10,11,12,13. However, the demonstrated approaches still require that the object is trapped at the high-light-intensity region. We report a new kind of optically controlled nanotweezers, called opto-thermo-electrohydrodynamic tweezers, that enable the trapping and dynamic manipulation of nanometre-scale objects at locations that are several micrometres away from the high-intensity laser focus. At the trapping locations, the nanoscale objects experience both negligible photothermal heating and light intensity. Opto-thermo-electrohydrodynamic tweezers employ a finite array of plasmonic nanoholes illuminated with light and an applied a.c. electric field to create the spatially varying electrohydrodynamic potential that can rapidly trap sub-10 nm biomolecules at femtomolar concentrations on demand. This non-invasive optical nanotweezing approach is expected to open new opportunities in nanoscience and life science by offering an unprecedented level of control of nano-sized objects, including photo-sensitive biological molecules. 
    more » « less
  5. ; ; ; ; ; ; ; ; ; ; et al (, Hyper-Raman optical activity of biologically relevant chiral molecules)
    The optical activity of Raman scattering provides insight into the absolute configuration and conformation of chiral molecules. Applications of Raman optical activity (ROA) are limited by long integration times due to a relatively low sensitivity of the scattered light to chirality (typically 10^-3 to 10^-5). We apply ROA techniques to hyper-Raman scattering using incident circularly polarized light and a right-angle scattering geometry. We explore the sensitivity of hyper- Raman scattering to chirality as compared to spontaneous Raman optical activity. Using the excitation wavelength at around 532 nm, the photobleaching is minimized, while the hyper-Raman scattering benefits from the electronic resonant enhancement. For S/R-2-butanol and L/D-tartaric acid, we were unable to detect the hyper-Raman optical activity at the sensitivity level of 1%. We also explored parasitic thermal effects which can be mitigating by varying the repetition rate of the laser source used for excitation of hyper-Raman scattering. 
    more » « less
  • Citation Formats
  • MLA
  • APA
  • Chicago
  • BibTeX
  • Save / Share this Record
  • Send to Email