Single Optical Measurement Research Articles

Ultrasound modulated bioluminescence tomography with a single optical measurement

Ultrasound modulated bioluminescence tomography is an imaging method which can be formulated as a hybrid inverse source problem. In the regime where light propagation is modeled by a radiative transfer equation, previous approaches to this problem require large numbers of optical measurements (Bal et al 2016 SIAM J. Math. Anal. 48 1332). Here we propose an alternative solution for this inverse problem which requires only a single optical measurement in order to reconstruct the isotropic source. Specifically, we derive two inversion formulae based on Neumann series and Fredholm theory respectively, and prove their convergence under sufficient conditions. The resulting numerical algorithms are implemented and experimented to reconstruct both continuous and discontinuous sources in the presence of noise.

Selection of optimal wavelengths for optical soiling modelling and detection in photovoltaic modules

Soiling impacts the photovoltaic (PV) module performance by reducing the amount of light reaching the photovoltaic cells and by changing their external spectral response. Currently, the soiling monitoring market is moving toward optical sensors that measure transmittance or reflectance, rather than directly measuring the impact of soiling on the performance of photovoltaic modules. These sensors, which use a single optical measurement, are not able to correct the soiling losses that depend on the solar irradiance spectra and on the spectral response of the monitored PV material. This work investigates methods that can improve the optical detection of soiling by extracting the full soiling spectrum profiles using only two or three monochromatic measurements. Spectral transmittance data, measured with a spectrophotometer and collected during a 46-week experimental soiling study carried out in Jaén, Spain, was analysed in this work. The use of a spectral profile for the hemispherical transmittance of soiled PV glass is found to significantly improve the soiling detection, returning the lowest errors independently of the PV materials and irradiance conditions. In addition, this work shows that it is also possible to select the measurement wavelengths to minimize the soiling loss detection error depending on the monitored PV semiconductor material (silicon, CdTe, a-Si, CIGS and a representative perovskite). The approaches discussed in this work are also found to be more robust to potential measurement errors compared to single wavelength measurement techniques.

Lifting degeneracy in nematic liquid crystal viscosities with a single optical measurement

The viscosity of complex, anisotropic fluids, such as liquid crystals or their colloidal suspensions, is characterized by a number of coefficients. Methods to measure them are, typically, sensitive only to their particular combinations, hence unable to determine them individually. Using an Ericksen-Leslie model and propagation of light through aligned layers of such materials, we show theoretically and verify experimentally how this degeneracy can be lifted by exploiting both the amplitude and frequency of the voltage applied to the cell as control parameters.

Optical mass sensing based on nanomechanical resonator systems

Nanomechanical resonator has attracted much attention because of its high Q factor, high vibration frequency, small size, high sensitivity and other excellent characteristics. With the rapid development of nanotechnology, nanomechanical system is widely employed in biology, chemistry, physics, medical sciences. Gradually, nanomechanical resonator becomes an auxiliary system for scientists to pursue some high quality and high performance materials. Here, we review one of the most important applications in our research group which is optical mass sensing based on nanomechanical resonator systems. The masses of neutral atoms, protons, neutrons and other chemical molecules and biological molecules can be measured in all-optical domain. Two nanomechanical resonators carbon nanotube and graphene nanoribbon are introduced. Compared with traditional electrical mass detection there are a lot of incomparable advantages for this optical mass sensing. For example, the heat effect and energy loss caused by circuits can be removed during the optical mass measurement, and the spectral width in optical sensing is narrower than in electrical technique. Furthermore, other than the single optical mass detection, the all-optical mass sensing is not restricted by the vibrational frequency of nanomechanical resonator, which will break many limitations in electrical method and single optical measurement. The all-optical mass sensing provides a new platform in nanoscale measurement, and has a promising to enhance the mass sensitivity and accuracy in the future.

Effects of tissue heterogeneity on the optical estimate of breast density

Breast density is a recognized strong and independent risk factor for developing breast cancer. At present, breast density is assessed based on the radiological appearance of breast tissue, thus relying on the use of ionizing radiation. We have previously obtained encouraging preliminary results with our portable instrument for time domain optical mammography performed at 7 wavelengths (635–1060 nm). In that case, information was averaged over four images (cranio-caudal and oblique views of both breasts) available for each subject. In the present work, we tested the effectiveness of just one or few point measurements, to investigate if tissue heterogeneity significantly affects the correlation between optically derived parameters and mammographic density. Data show that parameters estimated through a single optical measurement correlate strongly with mammographic density estimated by using BIRADS categories. A central position is optimal for the measurement, but its exact location is not critical.

Amplitude filter and Fourier-based modal method for quality control of microlenses array

We present a computer simulation and an experimental realization of an optical setup for automatic quality control of microlenses arrays. The method is based on a 4f correlator setup with an amplitude filter. The output intensity signal is simple to analyze and interpret because the intensity is proportional to the first derivative of the distortion of the input wavefront. This method is shift invariant, allows for the examination of single elements, or sets of micro-optical elements simultaneously, and is particularly suitable for assessing the quality of optical elements. However, combining the method with a more detailed analysis based on the Fourier modal method, allows for obtaining quantitative data. Although errors are within the 2-3% range, such an analysis enables a fast and relatively accurate comparison of numerous elements with each other and with the model. The combination has never been applied but allows for a fast and cost-effective analysis that can be used for industrial purposes. Both the methods give separate results for each lens or for all the lenses in the array, simultaneously. In the combination proposed, the analysis is computer-based and done on the basis of the initial single optical measurement.

Amplitude filter and Zernike polynomial expansion method for quality control of microlens arrays

This paper deals with a computer simulation and an experimental realization of an optical setup for automatic quality control of microlens arrays. The method is based on a 4f coherent light correlator setup with an amplitude filter placed in the Fourier plane. The output intensity signal is proportional to the first derivative of the distortion of the input wavefront. An analysis can be carried out with the use of the Zernike polynomial expansion method. It must be carried out separately for each lens, but it allows for a more precise, quantitative assessment of their quality. What is important is that the analysis is computer-based and performed on the basis of the initial single optical measurement.

Invited Article: Simultaneous mapping of temperature and stress in microdevices using micro-Raman spectroscopy

Analysis of the Raman Stokes peak position and its shift has been frequently used to estimate either temperature or stress in microelectronics and microelectromechanical system devices. However, if both fields are evolving simultaneously, the Stokes shift represents a convolution of these effects, making it difficult to measure either quantity accurately. By using the relative independence of the Stokes linewidth to applied stress, it is possible to deconvolve the signal into an estimation of both temperature and stress. Using this property, a method is presented whereby the temperature and stress were simultaneously measured in doped polysilicon microheaters. A data collection and analysis method was developed to reduce the uncertainty in the measured stresses resulting in an accuracy of +/-40 MPa for an average applied stress of -325 MPa and temperature of 520 degrees C. Measurement results were compared to three-dimensional finite-element analysis of the microheaters and were shown to be in excellent agreement. This analysis shows that Raman spectroscopy has the potential to measure both evolving temperature and stress fields in devices using a single optical measurement.

All electrical laser diode characterization by monolithic integration with a photodiode

Summary form only given. The combination of a laser diode integrated on top of a photodiode has been shown to be of interest as an electronic device for optoelectronic circuits (the photon transport transistor) and for reducing the power dissipation of a laser at thresholds up to 42% through photon recycling. The added photodiode also proves to be a powerful analysis tool for determining laser parameters, characterizing mirror processing, and studying laser diode degradation. Without a single optical measurement one can determine the laser threshold current, the nonradiative lifetime of the carriers, and the differential quantum efficiency. Early degradation of the laser diode was also studied by monitoring the light absorbed in the photodiode. >

The chemical dynamics of 1,4,8,11-tetraazacyclotetradecane nickel(II) perchlorate with several solvents. I. Thermodynamics of base adduct formation

A solvent adduct study of 1,4,8,11-tetraazacyclotetradecane nickel(II) perchlorate with the coordinating solvents acetonitrile, N,N-dimethylformamide (DMF), methyl sulfoxide (DMSO), and water by optical and nmr techniques is reported. The thermodynamic parameters ΔH°, ΔS°, and K eq for adduct formation are given for each solvent system. At 25 °C, the stability order is found to be DMF > CH 3CN > DMSO > H 2O. A comparison of the observed stability order and stabilities predicted by single optical measurements and solvent donicity is presented.