A self-scanned 1024 element photodiode array and minicomputer are used to measure the phase (wavefront) in the interference pattern of an interferometer to lambda/100. The photodiode array samples intensities over a 32 x 32 matrix in the interference pattern as the length of the reference arm is varied piezoelectrically. Using these data the minicomputer synchronously detects the phase at each of the 1024 points by a Fourier series method and displays the wavefront in contour and perspective plot on a storage oscilloscope in less than 1 min (Bruning et al. Paper WE16, OSA Annual Meeting, Oct. 1972). The array of intensities is sampled and averaged many times in a random fashion so that the effects of air turbulence, vibrations, and thermal drifts are minimized. Very significant is the fact that wavefront errors in the interferometer are easily determined and may be automatically subtracted from current or subsequent wavefrots. Various programs supporting the measurement system include software for determining the aperture boundary, sum and difference of wavefronts, removal or insertion of tilt and focus errors, and routines for spatial manipulation of wavefronts. FFT programs transform wavefront data into point spread function and modulus and phase of the optical transfer function of lenses. Display programs plot these functions in contour and perspective. The system has been designed to optimize the collection of data to give higher than usual accuracy in measuring the individual elements and final performance of assembled diffraction limited optical systems, and furthermore, the short loop time of a few minutes makes the system an attractive alternative to constraints imposed by test glasses in the optical shop.

Digital wavefront measuring interferometer for testing optical surfaces and lenses

Journal of Visual Communication and Image Representation

Plaques vulnerable to rupture are characterized by a thin and stiff fibrous cap overlaying a soft lipid-rich necrotic core. The ability to measure local plaque stiffness directly to quantify plaque stress and predict rupture potential would be very attractive, but no current technology does so. This study seeks to validate the use of Brillouin microscopy to measure the Brillouin frequency shift, which is related to stiffness, within vulnerable plaques. The left carotid artery of an ApoE−/−mouse was instrumented with a cuff that induced vulnerable plaque development in nine weeks. Adjacent histological sections from the instrumented and control arteries were stained for either lipids or collagen content, or imaged with confocal Brillouin microscopy. Mean Brillouin frequency shift was 15.79 ± 0.09 GHz in the plaque compared with 16.24 ± 0.15 (p < 0.002) and 17.16 ± 0.56 GHz (p < 0.002) in the media of the diseased and control vessel sections, respectively. In addition, frequency shift exhibited a strong inverse correlation with lipid area of −0.67 ± 0.06 (p < 0.01) and strong direct correlation with collagen area of 0.71 ± 0.15 (p < 0.05). This is the first study, to the best of our knowledge, to apply Brillouin spectroscopy to quantify atherosclerotic plaque stiffness, which motivates combining this technology with intravascular imaging to improve detection of vulnerable plaques in patients.

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Quantification of plaque stiffness byBrillouin microscopy in experimentalthin cap fibroatheroma

Current measurements of the biomechanical properties of cells require physical contact with cells or lack subcellular resolution. Here we developed a label-free microscopy technique based on Brillouin light scattering that is capable of measuring an intracellular longitudinal modulus with optical resolution. The 3D Brillouin maps we obtained of cells in 2D and 3D microenvironments revealed mechanical changes due to cytoskeletal modulation and cell-volume regulation.

Noncontact three-dimensional mapping of intracellular hydromechanical properties by Brillouin microscopy

Radially and azimuthally polarized beams can create needle-like electric and magnetic fields under tight focusing conditions, respectively, and thus have been highly recommended for optical manipulation. There have been reports on the superiority of these beams over the conventional Gaussian beam for providing a larger optical force in single beam optical trap. However, serious discrepancies in their experimental results prevent one from concluding this superiority. Here, we theoretically and experimentally study the impact of different parameters — such as spherical aberration, the numerical aperture of the focusing lens, and the particles’ size — on optical trapping stiffness of radially, azimuthally, and linearly polarized beams. The result of calculations based on generalized Lorenz–Mie theory, which is in good agreement with the experiment, reveals that the studied parameters determine which polarization state has the superiority for optical trapping. Our findings play a crucial role in the development of optical tweezers setups and, in particular, in biophysical applications when laser-induced heating in the optical tweezers applications is the main concern.

Efficient optical trapping with cylindrical vector beams.

A new laser differential confocal radius measurement (DCRM) is proposed for high precision measurement of radius. Based on the property of an axial intensity curve that the absolute zero precisely corresponds to the focus of the objective in a differential confocal system (DCS), DCRM uses the zero point of the DCS axial intensity curve to precisely identify the cat's-eye and confocal positions of the test lens, and measures the accurate distance between the two positions to achieve the high-precision measurement of radius of curvature (ROC). In comparison with the existing measurement methods, DCRM proposed has a high measurement precision, a strong environmental anti-interference capability and a low cost. The theoretical analyses and preliminary experimental results indicate that DCRM has a relative measurement error of better than 5ppm.

Laser differential confocal radius measurement.

A new real-time laser differential confocal microscopy (RLDCM) without sample reflectivity difference effects is proposed for imaging height topography of sample surface, which divides the confocal microscopy imaging light path into two confocal microscopy imaging paths before and after focus with the equal axial detector offset oriented in opposite direction. By dividing the difference of the two signals simultaneously detected from these two confocal imaging paths by the higher signal between these two signals, RLDCM separates the signal that comes from reflectivity heterogeneity from the topographic signal in real time for the first time. RLDCM significantly reduces the height topography imaging time by single-layer scanning for the sample surface with reflectivity heterogeneity, and it achieves high axial resolution and lateral resolution similar to CM by optimizing the axial detector offset. Theoretical analysis and experimental results demonstrate that RLDCM realizes the real-time surface imaging for line structures featuring Silicon Dioxide steps on a Silicon base and achieves 2-nm axial depth resolution without reducing lateral resolution.

Real-time laser differential confocal microscopy without sample reflectivity effects.

The invention belongs to the technical field of optical microimaging and spectral measurement, and relates to a high-spatial resolution laser differential confocal map microimaging imaging method and device. The core thought of the method is that a differential confocal detection technology is merged with a spectrum detection technology together, and a dichroic beam splitting system (13) is used to carry out nondestructive separation on Reyleigh scattering light and Raman scattering light, wherein the Raman scattering light is treated by spectrum detection, the Reyleigh scattering light is treated by geometric position detection, based on the characteristic that the position of a zero crossing point of a differential confocal curve (43) is accurately corresponding to the focus position, spectrum information of the excitation spot focus position is captured through zero crossing point triggering, the high-spatial resolution spectrum detection is realized, and a method and a device capable of realizing the high-spatial resolution spectrum detection on micro zones of samples are formed. The method and the device have the advantages of being accurate in location, high in spatial resolution, high in sensitivity of spectrum detection and controllable in measurement of focal spot size, and the like, and have a wide application prospect in the fields of biomedicine, evidence collection of tribunal, and the like.

Laser differential confocal map microimaging imaging method and device

A new laser differential reflection-confocal focal-length measurement (DRCFM) method is proposed for the high-accuracy measurement of the lens focal length. DRCFM uses weak light reflected from the lens last surface to determine the vertex position of this surface. Differential confocal technology is then used to identify precisely the lens focus and vertex of the lens last surface, thereby enabling the precise measurement of the lens focal length. Compared with existing measurement methods, DRCFM has high accuracy and strong anti-interference capability. Theoretical analyses and experimental results indicate that the DRCFM relative measurement error is less than 10 ppm.

Laser differential reflection-confocal focal-length measurement

The invention relates to a method and device for measuring multiple element parameters in differential con-focus (con-focus) interference manner, belonging to the technical field of optical precise measurement. The core thought of the invention is as follows: a differential con-focus (con-focus) measurement system is used for measuring the surface curvature radius of a spherical element, the vertex focal distance of a lens, the refraction index of a lens, the thickness of the lens and the axial clearance of a lens group, and a facial-contour interference measurement system is used for measuring the facial contour of an element surface to realize simultaneous measurement on multiple parameters of an element and high measurement precision. In the invention, the differential con-focus (con-focus) measurement system and the facial-contour interference measurement system are fused for the first time to measure parameters comprehensively; and in the process of measuring the multiple parameters of the element, a light path is unnecessary to regulate and a measured element is unnecessary to detach, thus, the measured element is not damaged and the measurement speed is high.

Weiqian Zhao

Papers

Laser differential confocal radius measurement.

Real-time laser differential confocal microscopy without sample reflectivity effects.

Laser differential confocal map microimaging imaging method and device

Laser differential reflection-confocal focal-length measurement

Method and device for measuring multiple element parameters in differential con-focus interference manner