There are three short wavelength infrared (SWIR) optical windows outside the conventionally used first near-infrared (NIR) window (650 to 950 nm). They occur in the 1000- to 2500-nm range and may be considered second, third, and fourth NIR windows. The second (1100 to 1350 nm) and third windows (1600 to 1870 nm) are now being explored through label-free linear and multiphoton imaging. The fourth window (2100 to 2350 nm) has been mostly ignored because of water absorption and the absence of sensitive detectors and ultrafast lasers. With the advent of new technology, use of window IV is now possible. Absorption and scattering properties of light through breast and prostate cancer, bone, lipids, and intralipid solutions at these windows were investigated. We found that breast and prostate cancer and bone have longer total attenuation lengths at NIR windows III and IV, whereas fatty tissues and intralipid have longest lengths at windows II and III. Since collagen is the major chromophore at 2100 and 2350 nm, window IV could be especially valuable in evaluating cancers and boney tissues, whereas windows II and III may be more useful for tissues with high lipid content. SWIR windows may be utilized as additional optical tools for the evaluation of collagen in tissues.

https://www.spiedigitallibrary.org/journals/journal-of-biomedical-optics/volume-22/issue-4/045002/Short-wavelength-infrared-optical-windows-for-evaluation-of-benign-and/10.1117/1.JBO.22.4.045002.pdf

Short wavelength infrared optical windows for evaluation of benign and malignant tissues.

Fluorescence anisotropy imaging in drug discovery.

A New Frontier of Science and Technology: Exploring and Visualizing the Dynamics of Mind and Brain

We introduce a new method for performing ultrafast imaging and tracking of surface plasmon wave packets that propagate on metal films. We demonstrate the efficiency of leakage radiation microscopy implemented in the time domain for measuring both group and phase velocities of near-field pulses with a high level of precision. The versatility of our far-field imaging method is particularly appealing in the context of ultrafast near-field optics.

Tracking surface plasmon pulses using ultrafast leakage imaging

Light Propagation in Highly Scattering Turbid Media: Concepts, Techniques, and Biomedical Applications

By varying the absorption coefficient and width of an intralipid–India ink solution in a quasi-one-dimensional experiment, we investigate the transition between the ballistic and the diffusive regimes. The medium’s attenuation coefficient changes abruptly between two different values within a single mean free path. This problem is analyzed both experimentally and theoretically, and it is demonstrated that the transition location depends on the scattering coefficient as well as on the measuring solid angle.

Transition from the ballistic to the diffusive regime in a turbid medium

By varying the absorption coefficient and width of an intralipid- India ink solution in a quasi one-dimensional experiment, the transition between the ballistic and the diffusive regimes is investigated. The medium's attenuation coefficient changes abruptly between two different values within a single mean-free-path. This problem is analyzed both experimentally and theoretically, and it is demonstrated that the transition location depends on the scattering coefficient as well as on the measuring solid angle.

The transition from the ballistic to the diffusive regime in a turbid medium

The dependence of the transition between the ballistic and the diffusive regimes of turbid media on the experimental solid angle of the detection system is analyzed theoretically and experimentally. A simple model is developed which shows the significance of experimental conditions on the location of the ballistic–diffusive transition. It is demonstrated that decreasing the solid angle expands the ballistic regime; however, this benefit is bounded by the initial Gaussian beam diffraction. In addition, choosing the appropriate wavelength according to the model’s principles provides another means of expanding the ballistic regime. Consequently, by optimizing the experimental conditions, it should be possible to extract the ballistic image of a tissue with a thickness of 1 cm.

https://www.spiedigitallibrary.org/journals/journal-of-biomedical-optics/volume-18/issue-10/106006/Effect-of-measurement-on-the-ballisticdiffusive-transition-in-turbid-media/10.1117/1.JBO.18.10.106006.pdf

Effect of measurement on the ballistic-diffusive transition in turbid media.

Nanophotonic circuitry requires an ability to externally control and analyze optical signals tightly confined in subwavelength volumes. Various schemes of surface plasmon (SP) routing have been presented using active and passive metasurfaces. One of the most appealing approaches is the use of plasmonic spin-orbit interaction where the incident light spin state is efficiently coupled to an orbital degree of freedom of the surface wave. Recently, a major attention has been drawn to an additional plasmonic degree of freedom - the transverse spin and some application for near-field plasmonic manipulations have been presented. Here we propose a spin-locking metasurface incorporating a transverse spin of the SP wave to selectively route the near-field beams. Owing to the combination of the oblique incidence of circularly polarized light with the accurately designed momentum matching of the grating we achieve a precise directional control over the plasmonic distributions. The experimental verification of the directional launching is performed by a time-resolved leakage radiation measurements allowing one to visualize the shape and the dynamics of the excited beam.

/pdf/spin-locking-metasurface-for-surface-plasmon-routing-1eti7fpw8v.pdf

Spin-locking metasurface for surface plasmon routing

The spin-dependent routing of surface plasmons on metal by use of mirror symmetric periodic metasurface is presented and analyzed. We incorporate the intrinsic transverse spin angular momentum of the plasmonic wave in order to efficiently couple the incident light carrying circular polarization to a desired direction. The combination of the oblique incidence of polarized light with the accurately designed momentum matching properties of the grating provides a perfect way to achieve a spin-locking metasurface that routes the plasmonic beams.

Andre Yaroshevsky

Papers

Transition from the ballistic to the diffusive regime in a turbid medium

The transition from the ballistic to the diffusive regime in a turbid medium

Effect of measurement on the ballistic-diffusive transition in turbid media.

Spin-locking metasurface for surface plasmon routing

Spin-locking metasurface for surface plasmon routing