SPECTRUMMATE: A Low-cost Spectrometer for Small Telescopes

TL;DR

SPECTRUMMATE addresses the need for affordable, portable spectroscopy on small telescopes by adapting the Sol'EX design to a low-cost, 3D-printed housing and SpaceLAB components. The instrument employs a folded optical path with a 1200 grooves/mm reflective grating, delivering a dispersion of about $\rho \approx 0.11~\mathrm{\AA}/\text{pixel}$ and a resolving power of roughly $R \approx 2546$ near $5500~\mathrm{\AA}$ in practice, enabling high-resolution spectra of bright sources. The paper documents end-to-end development, from optical configuration and parameter calculations to 3D-modeling, assembly, and data reduction, culminating in Sun spectra and H-alpha solar imaging that demonstrate educational applicability. The work highlights the instrument’s modularity, cost-effectiveness, and potential as a training tool for astronomy education and outreach, while outlining concrete improvements (e.g., material choices, motorized grating rotation, and automated stitching) for future iterations.

Abstract

This project presents the development and implementation of a compact spectrometer, named SPECTRUMMATE, tailored for small telescopes. Small telescopes offer several advantages: they are cost-effective, occupy less space, and are simpler to set up than larger instruments. This makes them particularly suitable for amateur astronomers and educational institutions with limited resources. Moreover, small telescopes can effectively observe bright celestial objects, enabling valuable contributions to astronomical projects. Based on the Sol'EX design, SPECTRUMMATE was constructed using optical components available at the Space and Applications Laboratory (SpaceLAB), University of Science and Technology of Hanoi, Vietnam. The instrument is designed to meet the specific needs of astronomers who require detailed analysis within the visible spectrum (SPECTRUMMATE can capture a waveband of 368 angstrom/image, spectral coverage from 4000 to 6600 angstrom, and resolving power R = 2546 at 5500 angstrom). To achieve optimal performance, the design process involved selecting and configuring optical elements, including a collimator, diffraction grating, and objective lens. Experimental setups were tested to minimize spectral dispersion while ensuring the system's compactness and ease of alignment. Spectra obtained by SPECTRUMMATE demonstrated efficient spectral calibration and the capability to capture high-resolution spectra of bright light sources, such as the Sun, making it a valuable tool for specialised spectroscopic observations. The modular design of SPECTRUMMATE also allows users to change its components easily to achieve the desired spectral range and resolution.

Figures (29)

• Figure 1: The Sol'EX spectrometer by builsol - a good example of an easy-to-build spectrometer.
• Figure 2: Holographic reflective diffraction gratings of dimension $25 \times 25 \times 6~mm$ by Thorlabs, Inc.
• Figure 3: The first configuration by Thorlabs, Inc. 1 - LED light source. 2 - Aspheric Condenser Lenses. 3 - Focusing Lens. 4 - Variable Slit. 5 - Imaging lens. 6 - Reflective Diffraction Grating. 7 - Viewing Screen. 8 - Light Barrier (blocks stray light from source). Image from Thorlabs manual.
• Figure 4: The second configuration by Thorlabs, Inc. 1 - LED light source. 2 - Focusing Lens. 3 - Adjustable Slit. 4 - Imaging lens. 5 - Reflective Diffraction Grating. 6 - Viewing Screen. 7 - Light Barrier (blocks stray light from source). Image from Thorlabs manual.
• Figure 5: Sol'EX optical configuration.