Change In Refractive Index Of Water Research Articles

Ultrasensitive Optical Detection of Water Pressure in Microfluidics Using Smart Reduced Graphene Oxide Glass.

Despite recent progresses in the field of microfluidics, the effect of liquid pressure on the detection accuracy has been rarely studied. Here, we perform a quantitative analysis of such effect, by utilizing the sensitive optical responses of graphene to the refractive index (RI) change of its surrounding environment. We utilize a reflection coupling configuration by combining the total internal reflection (TIR) and ultrasonic waves. The high-performance graphene is processed on common glasses by using the solution-processable oxidation-reduction method. We find that the RI change of water caused by a pressure as small as 500 Pa generated by the liquid level change in the microfluidics can be measured directly. The detection accuracy and response time limits are approximately 280 Pa and 100 ns, respectively. The Maxwell's boundary conditions, Fresnel's law, and Pascal's law are used in theoretical analyses. This work highlights the importance of liquid pressure in microfluidics and provides guidance in designing and accurate detection of microfluidic devices.

Theoretical Investigation of Surface Plasmon Resonance (SPR)-Based Acoustic Sensor

We report a theoretical investigation of a surface plasmon resonance (SPR)-based acoustic sensor for optical detection of ultrasound. The structure being studied is arranged in the Krestchmann configuration and the detection is performed by observing the change of refractive index of water next to the SPR metal. The acoustic pressure is simulated using COMSOL. The simulation results illustrate an insight into mechanism of pressure variation on the surface of SPR sensor due to a constructive interference of the ultrasound. This leads to a local refractive index change of water. The local refractive index change is calculated by converting the incident pressure to water density using IAPWS-95 formulation. Then, the water density is converted to the refractive index using Lorentz-Lorenz formulation. Here we report the change in the refractive index of the water to pressure, dn/dp, which is calculated to be 1.4 x 10-10 Pa-1, which is very close to the dn/dp reported by M. W. Sigrist 1986. We also investigated the effect of temperature and wavelength on the dn/dp and found that the variation in temperature and wavelength does not show any significant effect on the dn/dp relationship. We also discuss the effect of quality factor (Q) and possible improvements to enhance the sensitivity of SPR-based acoustic sensor.

Estimation of absolute sound pressure in a small-sized sonochemical reactor

A small-sized sonochemical reactor in which the absolute value of the sound pressure amplitude can be estimated from the vibration velocity of the transducer was investigated. The sound pressure distribution in the reactor and the relationship between the vibration velocity and the sound pressure amplitude were derived through Helmholtz wave equation. The reactor consists of a bolt-clamped Langevin transducer and a rectangular cell with a tungsten reflector. A 3λ/4-standing-wave-field was generated in the reactor to simplify the sound pressure distribution. The sound pressure distribution was measured from the optical refractive index change of water using a laser interferometer. The experimental and theoretical results showed a good agreement in the absolute value of the sound pressure amplitude, and it was confirmed that the sound pressure in the sonochemical reactor can be estimated from the input current of the vibrator.

Gigantic optical Pockels effect in water within the electric double layer at the electrode-solution interface

We have obtained the experimental evidence for the Pockels effect of water, which is placed in the electric double layer (EDL) on the interface between the bulk water and a transparent electrode. The electric-field induced energy shift was observed for the visible interference fringes in a 300-nm indium-tin-oxide (ITO) electrode layer. The signal was shown to originate from a negative (positive) refractive index change of water in the EDL for the positive (negative) bias. The refractive index change was as large as $\ensuremath{\Delta}n=\ensuremath{-}0.1$ for the 2-nm thick EDL. The Pockels constants of water in the EDL were determined to be ${r}_{13}=(2.0\ifmmode\pm\else\textpm\fi{}0.3)\ifmmode\times\else\texttimes\fi{}100\text{ }\text{pm}/\text{V}$ and ${r}_{33}=(2.5\ifmmode\pm\else\textpm\fi{}0.6)\ifmmode\times\else\texttimes\fi{}100\text{ }\text{pm}/\text{V}$. At the same time, the ITO showed blue shifts of both the band gap in the UV and the plasma frequency in the near infrared due to the band population effect in the space charge layer. Both shifts lead to a negative refractive index change in the visible region of the ITO, but their effect on the interference fringe shifts in the visible region was estimated to be much smaller than that of water in the EDL.

Temperature-insensitive miniaturized fiber inline Fabry-Perot interferometer for highly sensitive refractive index measurement

We report a miniaturized fiber inline Fabry-Perot interferometer (FPI), with an open micro-notch cavity fabricated by one-step fs laser micromachining, for highly sensitive refractive index measurement. The device was tested for measurement of the refractive indices of various liquids including isopropanol, acetone and methanol at room temperature, as well as the temperature-dependent refractive index of deionized water from 3 to 90 degrees C. The sensitivity for measurement of refractive index change of water was 1163 nm/RIU at the wavelength of 1550 nm. The temperature cross-sensitivity of the device was about 1.1x10(-6) RIU/degrees C. The small size, all-fiber structure, small temperature dependence, linear response and high sensitivity, make the device attractive for chemical and biological sensing.

Pockels effect of water in the electric double layer at the interface between water and transparent electrode

We have obtained the first experimental evidence for the Pockels effect of water, which is induced by a high electric field in the electric double layer (EDL) on the water–transparent electrode interface. The electric-field induced energy shift of the visible interference fringes of a 300 nm indium–tin–oxide (ITO) electrode layer is observed, indicating a negative refractive index change at the interface. Numerical calculation reproduces well the experimental observation, showing that the signal mainly originates from water in the EDL. The Pockels constants of water are estimated to be r 33 = 5.1 × 100 pm/V and r 13 = 1.7 × 100 pm/V. The large anisotropy of the Pockels effect of water is deduced from the incidence angle dependence of the p-polarization signal. At the same time, the ITO shows a blue shift of the band gap in the UV due to the band population effect in the space charge layer. The plasma frequency in the near IR is also expected to increase due to the band population effect, since the ITO has a high doped carrier population close to metal. A negative refractive index change in the ITO space charge layer is induced from both effects, but its effect on the signal is estimated to be much smaller than that of the negative refractive index change of water in the EDL.