Influence Of Spectral Bandwidth Research Articles

Influence of spectral bandwidth on the working curve in vat photopolymerization

In vat photopolymerization, 3-dimensional parts are fabricated by using patterned light to spatially cure a liquid resin. One of the foundational measurements for vat photopolymerization is known as the working curve whereby the depth (i.e. thickness) of cured resin is measured as a function of radiant exposure. The commonly applied mathematical model for the working curve – known widely as the Jacobs model – assumes a monochromatic light source. The Jacobs model has been widely used, but in many cases significant deviations between the Jacobs model and the data have been observed. Herein, we extend the Jacobs model by deriving a polychromatic model that accounts for broadband light sources (e.g. light emitting diodes, LEDs). We demonstrate through experiment and theory that in certain cases the deviations from Jacobs’ original model can be explained and understood as an optical ‘inner filter’ effect. The ability of the Jacobs model to capture the working curve behavior is shown to be dependent on the bandwidth of the light source in conjunction with the gradient in the absorption spectrum of the resin in the vicinity of the light source spectrum. Additionally, we offer an empirical model function that better fits experimental data and allows for an improved estimate of model parameters. Broadly, this work aims to strengthen the conceptual link between the working curve measurement and the photophysical parameters that are intrinsic to vat photopolymerization printing.

The influence of spectral bandwidth and shape on deep-water wave breaking onset

Deep-water surface wave breaking affects the transfer of mass, momentum, energy and heat between the air and sea. Understanding when and how the onset of wave breaking will occur remains a challenge. The mechanisms that form unforced steep waves, i.e. nonlinearity or dispersion, are thought to have a strong influence on the onset of wave breaking. In two dimensions and in deep water, spectral bandwidth is the main factor that affects the roles these mechanism play. Existing studies, in which the relationship between spectral bandwidth and wave breaking onset is investigated, present varied and sometimes conflicting results. We perform potential-flow simulations of two-dimensional focused wave groups on deep water to better understand this relationship, with the aim of reconciling existing studies. We show that the way in which steepness is defined may be the main source of confusion in the literature. Locally defined steepness at breaking onset reduces as a function of bandwidth, and globally defined (spectral) steepness increases. The relationship between global breaking onset steepness and spectral shape (using the parameters bandwidth and spectral skewness) is too complex to parameterise in a general way. However, we find that the local surface slope of maximally steep non-breaking waves, of all spectral bandwidths and shapes that we simulate, approaches a limit of$1/\tan ({\rm \pi} /3)\approx 0.5774$. This slope-based threshold is simple to measure and may be used as an alternative to existing kinematic breaking onset thresholds. There is a potential link between slope-based and kinematic breaking onset thresholds, which future work should seek to better understand.

Slit Width Effect on Signal-to-noise Ratio in Spectrophotometric Measurements

Signal-to-noise (S/N) ratio theory has proven to be useful in understanding, designing, and optimizing spectrophotometric measurement systems. Although a narrower spectral bandwidth does improve the resolution of closely spaced peaks, it also decreases the Signal-to-noise ratio. The narrowest slit width should be used that will yield an acceptable Signal-to-noise ratio. In this research, the wavelengths of peak absorbance of the holmium glass filter were determined to attain the optimum Signal-to-noise ratio accompanied with spectral bandwidths of 0.1 nm, 0.2 nm, 0.5 nm, 0.8 nm, 1 nm, 2 nm, 3 nm and 5 nm. The influence of spectral bandwidth on the Signal-to-noise ratio was by far the most important parameter affecting the location of the measured wavelengths of absorbance or transmittance of the sample.

Influence of Spectral Bandwidth and Position on Chlorophyll Content Retrieval at Leaf and Canopy Levels

Foliar chlorophyll content in vegetation ecosystems plays an important role in plant photosynthesis and it also can indicate vegetation stress and disturbance. Vegetation indices (VIs) which derived from the hyperspectral remote sensing data offer a nondestructive method for quick estimation of leaf and canopy chlorophyll content. However, the accuracy of chlorophyll retrieved by VIs depends on the spectral band information. It is a big problem how to select the suitable band and how to effectively evaluate the band position and bandwidth in chlorophyll estimation using remote sensing data. This study was focused on the impact of spectral band position and bandwidth on the chlorophyll retrieval at leaf and canopy levels. One hundred leaf spectral reflectance samples which were measured with an ASD spectroradiometer and 954 canopy reflectance samples which were simulated with the PROSAIL model were used in the study. First, the variable interval spectral average method was used to generate the plant spectra with different band position and bandwidth at leaf and canopy level. And then, linear regression model was used to build the relationship between chlorophyll (Chl) and two-band VIs (Normalized Difference Vegetation Index, NDVI; Chlorophyll Index CI; Simple Ratio Index SR). With this model, the accuracy of Chl was evaluated when varying spectral band position and bandwidth. At last, by comparing accuracies, the optimized spectral band position and bandwidth for Chl retrieval were identified. The results showed that the bandwidth and position of the spectral data could significantly affect the accuracy on Chl retrieval at both leaf and canopy levels. The optimal bandwidth on retrieval Chl would be less than 30 nm and greater than 10 nm at both leaf and canopy levels when using linear regression model. At leaf level, the optimal bands were in 748–786 nm and in 713–732 nm respectively. At canopy level, the optimal bands were in 770–750 and 765–738 nm respectively when using two-band VIs (NDVI, SR, and CI) to estimate Chl.

Thin‐layer response and spectral bandwidth

A derivation is presented of the response of an embedded thin layer to a vertically incident seismic pulse. The reflected pulse has the shape of the time derivative of the incident‐wavelet, and its amplitude is proportional to the two‐way traveltime in the thin layer and to a factor depending upon the ratio of acoustic impedances. The influence of spectral bandwidth on interface resolution and thin‐layer response is investigated by means of zero‐phase signals, and a filtering philosophy is proposed which enables thickness estimation either from amplitude or from peak‐to‐trough time.