Spatial and spectral features of the luminescence of liquid nitrogen stimulated by infrared lasers

Spectral features of cryogenic liquids, especially nitrogen, seem to be clearly investigated due to the wide application in science. On the other hand, material properties can really be different under intensive laser irradiation. During irradiation of liquid nitrogen with pulsed (pulse duration 20 ns) YaG: Nd 1064 nm laser with average power of 0.3 W we have found bright luminescence in the visible region with five narrow spectral lines. This phenomenon can be explained by the multiphoton excitation of nitrogen molecules and ions with infrared photons. Its spatial and spectral characteristics are attributed to Amplified Spontaneous Emission. The main features include super-linear dependence of the emission intensity on the intensity of the excitation radiation, limited amount of narrow spectral bands and conical geometry of the emission with the clear separation of the cones in correspondence with the spectral lines of the emission. This phenomenon manifests liquid nitrogen as the convenient substance of Kerr type for studies of various non-linear optical processes by means of nanosecond lasers instead of femtosecond lasers applied usually for these purposes.

A Cost-Efficient Multiwavelength LED-Based System for Quantitative Photoacoustic Measurements

The unique ability of photoacoustic (PA) sensing to provide optical absorption information of biomolecules deep inside turbid tissues with high sensitivity has recently enabled the development of various novel diagnostic systems for biomedical applications. In many cases, PA setups can be bulky, complex, and costly, as they typically require the integration of expensive Q-switched nanosecond lasers, and also presents limited wavelength availability. This article presents a compact, cost-efficient, multiwavelength PA sensing system for quantitative measurements, by utilizing two high-power LED sources emitting at central wavelengths of 444 and 628 nm, respectively, and a single-element ultrasonic transducer at 3.5 MHz for signal detection. We investigate the performance of LEDs in pulsed mode and explore the dependence of PA responses on absorber’s concentration and applied energy fluence using tissue-mimicking phantoms demonstrating both optical absorption and scattering properties. Finally, we apply the developed system on the spectral unmixing of two absorbers contained at various relative concentrations in the phantoms, to provide accurate estimations with absolute deviations ranging between 0.4 and 12.3%. An upgraded version of the PA system may provide valuable in-vivo multiparametric measurements of important biomarkers, such as hemoglobin oxygenation, melanin concentration, local lipid content, and glucose levels.

Direct U-Pb dating of carbonates from micron scale fsLA-ICPMS images using robust regression

U-Pb dating of carbonates by LA-ICPMS spot analysis is an increasingly used method in the field of geosciences, as it brings very strong constraints over the geological history of basins, faults or reservoirs. Most ages currently published are based on the measurement of U and Pb ratios on spot ablations, using nanosecond lasers coupled to sector-field or multi-collector ICPMS. Here, we present a new strategy for the U-Pb dating of carbonates from 2D isotopic ratio maps, based on the use of a robust regression approach in the data reduction workflow. The isotopic maps, having minimum area of 0.65 mm2 (∼ 1000 pixels of 13 x 25 µm resolution), are obtained using a 257 nm femtosecond laser ablation system at high repetition rate (500 Hz) coupled to a High Resolution ICPMS. The maps commonly show significant variations in isotope ratios at the pixel scale, allowing the plotting of pixel U-Pb ratios in concordia or isochron diagrams and the calculation of U-Pb ages. Due to the absence of individual ratio uncertainties, the ages are calculated by using MM-robust linear regression rather than the more commonly used York-type regression. Provided examples demonstrate that this strategy allows calculating ages and uncertainties similar to those obtained for samples already dated by more traditional techniques (isotope dilution or LA-ICPMS spot analyses). The goodness-of-fit to the data is assessed by the calculation of the residual standard error of the regression (RSE), and by the calculation of a MSWD on discretized data. The regression method proposed is a statistically robust, alternative approach to that proposed by Drost et al. (2018), that can be easily applied to U-Pb age determination from isotopic maps.