Absorption of light by water in the region of high transparency: recommended values for photon-transport calculations

Practical Guidance for Developing Small-Molecule Optical Probes for In Vivo Imaging

The WMIS Education Committee (2019-2022) reached a consensus that white papers on molecular imaging could be beneficial for practitioners of molecular imaging at their early career stages and other scientists who are interested in molecular imaging. With this consensus, the committee plans to publish a series of white papers on topics related to the daily practice of molecular imaging. In this white paper, we aim to provide practical guidance that could be helpful for optical molecular imaging, particularly for small molecule probe development and validation in vitro and in vivo. The focus of this paper is preclinical animal studies with small-molecule optical probes. Near-infrared fluorescence imaging, bioluminescence imaging, chemiluminescence imaging, image-guided surgery, and Cerenkov luminescence imaging are discussed in this white paper.

Wander and spread of a perfect Laguerre-Gauss beam under turbulent absorbent seawater

The wander and long-term spread of a beam caused by turbulence are two important factors affecting channel targeting and information receiving in optics communication systems. In this paper, the wander and long-term spread of a perfect Laguerre-Gauss (PLG)/circular perfect Laguerre-Gauss (CPLG) beam in turbulent absorbing seawater are studied. The analytical expression of the wander for a CPLG beam in the weak turbulent fluctuation region and the analytical expression of the long-term spread for a CPLG beam in a weak to strong turbulent fluctuation region are derived by using the Rytov approximation and the generalized Huygens-Fresnel integral, respectively. Through numerical analysis, we find that the optimal beam diameter and self-convergence effect of the PLG beam exist under given communication link conditions, the long-term spread of PLG beam is smaller than that of the LG beam, but the wander evolution trend of the PLG beam with increasing propagation distance is opposite to that of the LG beam. PLG and CPLG beams have stronger resistance disturbance of turbulence than that of Laguerre-Gauss and circular Laguerre-Gauss beams, respectively.

Bit-error rate and average capacity of an absorbent and turbulent underwater wireless communication link with perfect Laguerre-Gauss beam

The proper selection of signal source structure and parameters is one of the effective methods to suppress the random disturbance of underwater channel and enhance the performance of link communication. In this paper, the bit error probability and average capacity of a weakly turbulent absorbing seawater link with a perfect Laguerre-Gaussian beam are studied. The bit error rate of orbital angular momentum (OAM) channel under on-off key modulation is derived. The average capacity model of the optical wireless communication link is established on the basis that the OAM channel formed by vortex carrier of topological charge m is symmetric channel. The relationship between OAM channel capacity, carrier wavelength and seawater absorption is numerically analyzed by seawater spectral absorption coefficient, and it is concluded that in the range of "window transmission wavelength" and long channel, the conclusion of the longer signal source wavelength is beneficial to the performance of non-absorptive turbulent channel is no longer valid. Some other numerical results are worked out to show that the underwater communication link with perfect Laguerre-Gaussian beam can obtain high channel capacity by adopting low OAM topological charge, smaller aperture of transmitter as well as receiver.

Received probability of perfect optical vortex in absorbent and weak turbulent seawater links

We investigated the effects of absorbent and weak turbulent seawater channels on the orbital angular momentum (OAM) mode carried by perfect optical vortex (POV) based on the Rytov approximation. After deriving the received probability of OAM modes, some numerical results are worked out to show that the receiving probability of OAM modes decreases linearly with the increase of virtual refractive index of the water body. An underwater communication link with POV as the signal carrier can obtain high receiving probability by adopting long signal wavelength in intervals of "seawater window wavelength," low OAM quantum number, a POV with a larger ring radius, and a transmitter as well as receiver with a smaller aperture. The transmission distance of OAM mode carried by POV in four kinds of seawater is better than that of a Bessel-Gaussian beam.

Received Probability of Orbital-Angular-Momentum Modes Carried by Diffraction- and Attenuation- Resistant Beams in Weak Turbulent Oceans

High performance underwater wireless optical communication systems are the key to the construction of high quality underwater optical communication networks. However, seawater absorption and seawater turbulent diffraction should be the main factors limiting the performance of underwater optical communication systems. For this reason, we established the probability model of the orbital angular momentum (OAM) mode received by the communication system to study the influence of the absorbable turbulent seawater channel on the underwater optical communication system with an anti-diffraction and anti-attenuation random (DARR) beam as the signal carrier. In the study, the DARR beam with a large truncated Gaussian aperture was adopted as the signal carrier, seawater absorption was characterized by the complex refractive index of seawater, and seawater turbulence was described by the power spectrum of the refractive index of seawater. By analyzing the relationship between the received probability of the OAM mode of DARR beams and the dissipation rate of kinetic energy per unit of mass of fluid, the ratio of temperature and salinity, dissipation rate of the mean-squared temperature, and other parameters, we show that one can select longer wavelength, smaller OAM quantum number and smaller received diameter to increase the received probability of OAM signal modes. The disturbance of turbulent seawater to the OAM modes with different quantum numbers carried by the DARR beam is less than the corresponding OAM modes carried by the Laguerre–Gaussian beam. Our paper shows that the DARR beam can mitigate the absorption and disturbance of turbulent seawater.

Impacts of pure seawater absorption coefficient on remotely sensed inherent optical properties in oligotrophic waters

The spectral absorption coefficient of pure seawater (a_w(λ)) in published studies differ significantly in the blue domain, yet the impacts of such discrepancies on the inherent optical properties (IOPs) derived from ocean color have been scarcely documented. In this study, we confirm that changes in a_w(λ) may have significant impacts on retrieved IOPs in oligotrophic waters, especially for the phytoplankton absorption coefficient (a_ph(λ)). Two sets of a_w(λ) data, a_w_PF97 (Appl. Opt. 36, 8710, 1997) and a_w_Lee15 (Appl. Opt. 54, 546, 2015), were selected for optical inversion analysis. It is found that a_ph(λ) retrieved with a_w_Lee15 agree better with the in-situ measurements in oligotrophic waters. Further applications to satellite images show that the derived a_ph(λ) using a_w_Lee15 can be up to 238% higher than the retrievals using a_w_PF97 in the core zone of the subtropical ocean gyres. Given that a_w_PF97 is commonly accepted as the "standard" a_w(λ) by the ocean color community in the past decades, this study highlights the need and importance to update a_w(λ) with a_w_Lee15 for IOPs retrievals in oligotrophic waters.