Fabricating a Raman spectrometer using an optical pickup unit and pulsed power

Abstract

Young chai cho & Sung il Ahn * Although Raman spectroscopy is a major analytical tool in modern chemical experiments, commercial Raman spectrometers remain very pricey for educational and research purposes in individual university laboratories. thus, this study focused on the structural similarity between the Raman spectrometer and an optical pickup unit (opU), which is an inexpensive compact optical device used for a part of optical discs. the study investigated whether or not a full set of Raman spectrometer can be developed at a cost of less than 1,000 US$. The OPU-based Raman spectrometer was fabricated using 3D printer-made components, a Raman edge filter, and a laser diode with a wavelength of 520 nm as the light source. A function generator was used as a pulsed power source to analyze the characteristics of the opU Raman spectrometer according to various frequencies and duty ratios. When using a pulsed DC power supply, the laser wavelength tended to move to a longer wavelength with increases in duty ratios. that is, the higher the frequency at the same duty ratio, the weaker the background light intensity compared with the scattered Raman signal intensity. The findings illustrate that Raman signal strength can be adjusted by adjusting the focal length of the objective lens of the OPU through an external adjustment of an additional DC power. In the Raman spectra of all solid and liquid samples used, the maximum error rate reached approximately 11 cm −1 , whereas the maximum intensity deviation reached approximately ± 6%. The cost of the complete OPU Raman spectrometer is less than 1,100 US$ using a function generator as power source and less than 930 US$ using a DC adapter. If the optical density (OD) 6 filter can be replaced with the OD 4 filter, then the costs are expected to decrease to approximately 730 US$. Raman spectrometers are very powerful tools used for the simple and rapid identification of chemical species in chemical-related laboratories. In particular, it is considered one of the essential spectroscopic methods along with the research and development of low-dimensional carbon compounds, such as carbon nanotubes, graphene, and carbon dots 1-6. Since C. V. Raman discovered Raman scattering in 1928 7 , various Raman spectrometers have been developed after extensive research and improvement. Light scattering can be classified into Mie and Rayleigh scatterings dependent on the size of scattering materials 8. Mie scattering is a phenomenon in which the light of all colors is scattered evenly regardless of the wavelength due to particle sizes that are larger than the incident wavelengths of lights. When the size of the scattering matter is much smaller than the wavelength of light, the difference lies in the degree of scattering according to the wavelength of the incident light. The second form, namely, Rayleigh scattering, causes the sky to appear blue. Most photon incidents on a molecule undergo Rayleigh scattering at the same wavelength as the incident light. However, a few photons scatter inelas...

A study on signal enhancement of a Raman probe using an optical pickup unit

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“…In this study, a Raman probe was developed using an OPU because the structural characteristics of a Raman spectrometer are similar to those of an OPU ( Figure 1 a). An OPU-based Raman system has been reported in previous studies [ 23 , 24 ]. However, the fabrication method discussed in previous studies is extremely complicated for educational purposes because of the replacement of multiple OPU parts with optical components.…”

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