4/28/2023 0 Comments Igor pro background image in graph![]() If the fluorescence baseline is high, the shot noise generated by this signal may be of a similar order, or even greater than the Raman signal alone and will completely mask the signal from the Raman photons. As a result, very low amounts of fluorescent species in the sample may be enough to mask the low Raman scattered photons or make it difficult to interpret the spectrum. Typically, one Raman photon is generated for every 106 to 109 laser photons incident upon the sample. It is well known that Raman scattering is an inefficient phenomenon. 1 This is reported to be a better alternative to conventional subtraction strategies2-4 by virtue of its compatibility with automated high-speed chemical analysis in the presence of fluorescence background. Advances in compressive detection strategy have recently been made to facilitate Raman classification and quantitation in the presence of fluorescence background. In contrast to the 514nm laser excitation line that produced significant fluorescence baseline, a better S/N ratio HPMC spectrum is acquired with 785nm excitation wavelength. ![]() The figure illustrates the loss of Raman peaks in the presence of increasing levels of fluorescence with high energy excitation sources. Bottom (785nm): 60s, 68mW at the sample.įigure 1 shows spectra of an inactive pharmaceutical ingredient, hydroxypropyl methylcellulose (HPMC), a common pharmaceutical excipient, which is measured at three different laser lines 514nm, 633nm and 785nm. Top spectrum (514nm): 5s, 77mW at the sample. This effect is illustrated in Figure 1.įigure 1: Spectra of HPMC obtained with 514nm, 633nm and 785nm laser lines. As the laser line moves to the near-infrared (NIR) region, as with 785nm or 1,064nm laser, the fluorescence effect subsides or completely disappears since the energy of these wavelengths may not be sufficient to excite the molecule to higher electronic state or may not be enough to destroy fluorescing molecules in the material. Higher energy green or red excitation sources, such as 514nm or 633nm visible laser, produce stronger fluorescence background. Raman scattering and fluorescence emission may compete with each other when the excitation laser energy is close to the electronic transition energy of the material. The phenomenon depends strongly on the excitation wavelength and appears only at a fixed frequency, while the Raman shifts are independent of the laser’s wavelength. Fluorescence light is then emitted while molecules relax back to the lower energy level. It is an absorption process that causes molecules to be excited to a higher electronic state, which requires high-energy photons. Print ( '|) plot_to_blog ( fig, 'xrd-fitting-xrd-data-complex-lmfit.The fluorescence interference in Raman spectroscopy may result from the compound analysed or from fluorescent impurities in the sample. Tedious parts of writting our own fitting software. Will use the excellent python package lmfit which automates all the Our own peak fitting software that is just as successful. ![]() In this post I will show how with numpy and scipy alone we can create Obscure the simple mathematics taking place behind the scenes. Softwares to do this job such as Origin Pro Peak Fitting, IGOR Pro, But the mathematician side of me neverīelieved it! There are numerous commercially available and open source As a material scientist I had alwaysīeen told that fitting is hard. It turns out that all XRD profiles are a combination of gaussians, These patterns when measures with a camera along all angles Technique where you point an x-ray beam at a material in a set angleĪnd observe the resulting angles and intensities of the diffractedīeam. One of the techniques ourĮxperimentalists use regularly is x-ray diffraction (XRD). Our group studies theįundamental physics behind ion beam modification and radiation While it may not be apparent on my blog, I am graduate student
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