Fast Spectral Measurements Research Articles

A Radio Frequency Tagging Continuous-Wave Optical Spectrometer With Megahertz Refreshing Rate

Optical spectrometers capable of fast spectral measurements are useful in many fields spanning from industrial manufacturing to scientific research. However, conventional spectrometers, especially those applicable to continuous-wave light measurements, are limited in speed due to the need of taking multiple measurements sequentially and/or direct current (dc) detection that are subject to noise influence. We report a new radio frequency (RF) tagging spectrometer, which breaks these limitations and dramatically accelerates measurements. In this new spectrometer, an acousto-optic deflector (AOD) is used to encode the intensity at each wavelength to the amplitude of a different beat RF signal. As a result, all RF signals can be summed up and detected simultaneously by a fast single-channel detector. The spectrum is obtained by taking the Fourier transform of the summed RF signal. The spectrometer is evaluated by measuring both multiline and broadband light sources with a speed up to 1 MHz as well as light scattering spectra with a speed of 64 kHz. With the ability to select wavelengths by programming the driving RF signal, the spectrometer offers great flexibility to detect part of a spectrum that contains most useful information with an unprecedented speed limit up to multiple megahertz.

High-power portable terahertz laser systems

Terahertz (THz) frequencies remain among the least utilized in the electromagnetic spectrum, largely due to the lack of powerful and compact sources. The invention of THz quantum cascade lasers (QCLs) was a major breakthrough to bridge the so-called ‘THz gap’ between semiconductor electronic and photonic sources. However, their demanding cooling requirement has confined the technology to a laboratory environment. A portable and high-power THz laser system will have a qualitative impact on applications in medical imaging, communications, quality control, security and biochemistry. Here, by adopting a design strategy that achieves a clean three-level system, we have developed THz QCLs (at ~4 THz) with a maximum operating temperature of 250 K. The high operating temperature enables portable THz systems to perform real-time imaging with a room-temperature THz camera, as well as fast spectral measurements with a room-temperature detector. GaAs-based terahertz quantum cascade lasers emitting around 4 THz are demonstrated up to 250 K without a magnetic field. To elevate the operation temperature, carrier leakage channels are reduced by carefully designing the quantum well structures.

Elucidating the Variability of Magnesium Stearate and the Correlations With Its Spectroscopic Features

The objective of this study is to investigate the variability in physiochemical and spectral properties of commercially available vegetable-grade magnesium stearate (MgSt) samples and to assess the correlation between physiochemical properties and near-infrared and Raman spectroscopic features to determine if fast spectral measurements could be used for physical and chemical evaluation. Thirteen MgSt samples of 9 manufacturer grades were obtained from 3 suppliers. The chemical composition was examined using gas chromatography and loss on drying. The physical characteristics were examined on 3 levels: solid state, particle, and bulk level. Comparing the largest to the smallest test values of 13 samples, the variation of the properties ranged from 7% to 335%, with majority of them varying by more than 100% of the smallest value. The samples could be categorized into 4 groups based on solid state properties (1) monohydrate, (2) dihydrate, (3) mixture of monohydrate and dihydrate, and (4) anhydrous form. Scanning electron microscopy images revealed 2 morphological types: thin, flat, and plate-like crystal habit versus irregular crystal habit. The overall variability was mapped using Principal Component Analysis. The greatest variation was due to different manufacturers and perhaps manufacturing methods and starting materials. Based on correlations to physiochemical properties of MgSt, near-infrared and Raman spectra showed potential as a rapid technique for evaluating the differences in excipient properties.

FTIR spectroscopy as a tool to detect contamination of rocket (Eruca sativa and Diplotaxis tenuifolia) salad with common groundsel (Senecio vulgaris) leaves

Rocket is a popular salad vegetable used all over the world and it has many health benefits. However, like with all plant material, there exists a danger of contamination with toxic substances. In the case of rocket, contamination with groundsel has occurred. Groundsel is a common weed in rocket crops, and it contains very toxic pyrrolizidine alkaloids. In our study infrared spectroscopy was used to distinguish groundsel samples from rocket leaves. Infrared spectroscopy is a very simple analytical technique; however, some specific conditions are more easily implemented in industrial environment than others. Some of these conditions and parameters of infrared spectroscopy were explored in detail. We tested for the influence of different parameters of attenuated total reflectance and transmission infrared method. Our results show that a 100 % correct classification can be obtained under conditions most suitable for industry: using fresh samples and parameters that enable fast spectral measurement. Infrared spectroscopy is a fast and easy-to-use method that has been shown to be able to differentiate between rocket and groundsel leaves. Therefore, it could be further studied for implementation in the safety control of rocket salads. © 2016 Society of Chemical Industry.

High-$T_{c}$ Josephson Square-Law Detectors and Hilbert Spectroscopy for Security Applications

Among various discussed ways of explosive detection, the techniques using electromagnetic radiation are considered as having great potential and research activities are recommended in this field. To identify new threats, like liquid explosives, with low rate of false alarms, fast spectral measurements are required in a broad frequency range from microwave to terahertz. We attract attention to a great potential of high-Tc Josephson technology in security applications and present our results in developing high-Tc Josephson junctions for Hilbert spectroscopy and detector arrays.

Ultra-Fast Optical Spectrum Analyzer for DWDM Applications

Dense wavelength division multiplexing optical networks use tunable devices such as distributed Bragg reflector laser diodes. These optical sources require a precise wavelength calibration according to the ITU grid, even with aged components. Some specific optical spectrum analyzers are commercially available. Unfortunately, measurements using those systems are generally relatively slow. We present and discuss in this paper a fast spectral measurement system that can easily be implemented in a laser diode package.