Scanning focused refractive-index microscopy

Abstract

We present a novel scanning focused refractive-index microscopy (SFRIM) technique to obtain the refractive index (RI) profiles of objects. The method uses a focused laser as the light source, and combines the derivative total reflection method (DTRM), projection magnification, and scanning technique together. SFRIM is able to determine RIs with an accuracy of 0.002, and the central spatial resolution achieved is 1 µm, which is smaller than the size of the focal spot. The results of measurements carried out on cedar oil and a gradient-refractive-index (GRIN) lens agree well with theoretical expectations, verifying the accuracy of SFRIM. Furthermore, using SFRIM, to the best of our knowledge we have extracted for the first time the RI profile of a periodically modulated photosensitive gelatin sample. SFRIM is the first RI profile-resolved reflected light microscopy technique that can be applied to scattering and absorbing samples. SFRIM enables the possibility of performing RI profile measurements in a variety of applications, including optical waveguides, photosensitive materials and devices, photorefractive effect studies, and RI imaging in biomedical fields.

Quantitative index imaging of coculture cells by scanning focused refractive index microscopy

“…All information is collected with Labview software. Because the detector receives part of the reflected light, spatial resolution of SFRIM is 0.8 and 3.7 μm in horizontal directions, 13 smaller than the size of the focal point. The incident angle of the focused beam varies across a range that covers the critical angle θ c at the sample-prism interface, and the angle-dependent reflectance curve can be directly recorded by the detector.…”

“…In our previous study, SFRIM has been applied to waveguides, photochromic materials, and photorefractive materials. 13 The spatial discrimination of SFRIM is significantly better than traditional reflection-based methods. The RI information is deduced with the simple derivative total internal reflection method, while the complex retrieval algorithm or reconstruction process is unnecessary.…”

“…The precision of RI estimation is less than 0.002. 13 Differently from the SSPM methods, a coated metal film is not needed in our apparatus. The cells are cultured directly on the prism.…”

Measurement of refractive index distribution of biotissues by scanning focused refractive index microscopy

“…The newly emerged scanning focused refractive index microscopy is applied to measure refractive index profiles of optical waveguides and photosensitive materials, and is a potential TIR-based technique for RI imaging of biological tissues. 17 In this study, we present the subtle tissue RI information with the improved SFRIM spatially adapted to the observation of unstained porcine muscle slices. Some slight modifications are made to the SFRIM for better two dimension (2-D) observation of the tissues.…”

“…A: Attenuator. MO1: 50× microscopy objective; P: trapezoidal prism; S: sample; D: detector (Hamamatsu S3903-512Q); MO2: 10× microscopy objective; CCD: Charge Coupled Device (CXE-B013-U, Mightex System, Canada); PC: personal computer.Because the detector received part of the reflected light, spatial resolution of SFRIM is 0.8 m μ along X-axis and 3.8 m μ along Y-axis, smaller than size of the focal spot 17. When SFRIM is applied to 2-D measurement, spatial resolution along Y-axis changes slightly.…”