3D-printed microscope with illumination for undergraduate wave optics laboratory

We present an educational tool, a microscope with a video camera, that can be fabricated either from a standard microscope or assembled from inexpensive, commercially available components (objectives, beam splitters, LEDs, linear stages) and 3D-printed elements. Usage of interference filters in combination with white light-emitting diode (LED) illumination enables the quantitative study of optical phenomena such as refraction, interference (e.g., Newton’s rings), Fresnel and Fraunhofer diffraction. Thus, we propose an instrument that can be used to illustrate the theoretical foundations of an undergraduate optics course and beyond.

💡 Research Summary

The paper presents a low‑cost, modular microscope designed specifically for undergraduate wave‑optics laboratories. The instrument can be built either by retrofitting a conventional microscope or by assembling inexpensive, commercially available components—objective lenses, beam splitters, LEDs, linear stages—and a 3D‑printed PETG frame. The core optical architecture follows an infinity‑corrected scheme: a plan‑achromatic objective projects the sample onto a collimated beam, which is then focused onto a camera sensor by a tube lens placed at its focal plane. Because the objective forms a parallel beam, the distance between objective and camera does not affect image quality, allowing easy insertion of additional optics such as filters, polarizers, or beam splitters without degrading performance.

Two illumination configurations are implemented. In the top‑illumination (reflection) mode, a white LED passes through a selectable interference filter, a focusing lens (Lens 1), and a 45° beam‑splitting plate before reaching the objective’s entrance pupil. The beam‑splitting plate is a 50/50 dielectric coating with an anti‑reflection side facing the LED, ensuring a balanced mix of reflected and transmitted light. In the bottom‑illumination (transmission) mode, a pinhole/iris acts as a point source; a second achromatic lens (Lens 2) collimates the light, providing either nearly parallel illumination for diffraction experiments or slightly divergent illumination for Newton’s‑ring measurements. The interchangeable interference filters (10–40 nm bandwidth) give quasi‑monochromatic illumination while retaining the uniformity of an LED source.

Resolution is limited by diffraction (δ ≈ λ/(2 NA)) and by the camera pixel size (≈3 µm). The authors use objectives of 5× (NA 0.15), 10× (NA 0.30), and 20× (NA 0.40) together with a 100 mm tube lens, achieving pixel‑limited resolutions several times finer than the diffraction limit. Validation is performed with micro‑structured test targets such as CD, DVD, HD‑DVD, and Blu‑ray discs; the smallest 0.32 µm track of a Blu‑ray is resolved only with violet illumination and the highest‑NA objective, demonstrating the system’s capability to explore sub‑micron features.

The educational value lies in the assembly process itself. Students must thread coarse and fine 3D‑printed screws, align the tube lens by focusing on a distant object, calibrate the vertical translation stage by focusing on the top and bottom surfaces of a calibrated glass block, and understand the physics of beam‑splitter coatings (reflection vs. transmission, optimal R = T = 0.5 for maximal product TR). The microscope enables a suite of classic optics experiments:

1. Refractive‑index measurement – By recording the Z‑stage positions (h₁, h₂, h₃) when focusing on the bottom surface, top surface of a transparent plate, and the substrate, the index is calculated via n = (h₂ − h₃)/(h₂ − h₁). The authors achieved ~1 % accuracy for glass and sapphire plates of 1 mm thickness.

2. Newton’s rings – Both reflected and transmitted configurations are demonstrated. Students can measure ring radii, plot r² versus ring order, and extract the wavelength or curvature radius of the lens.

3. Diffraction experiments – A lithographic mask containing slits, gratings, and pinholes is placed in the collimated beam. Students record Fresnel and Fraunhofer patterns, measure fringe spacings, and compare with theoretical predictions.

4. Resolution tests – Using the disc patterns mentioned above, students quantify the system’s lateral resolution and explore the effect of NA, illumination wavelength, and magnification.

5. Scale calibration – By moving the focus between known height steps on a calibrated block, the Z‑stage’s micrometer scale is verified.

Potential extensions include replacing the 50/50 beam splitter with a dichroic or cube splitter for fluorescence or photoluminescence studies, adding polarizers for polarization microscopy, integrating a simple condenser for higher‑angle illumination, or employing the platform for machine‑vision projects. The open‑source software ToupView provides real‑time image acquisition and quantitative analysis, further lowering the barrier for student use.

Limitations are acknowledged: high‑NA objectives have a very shallow depth of field (≈λ/NA²), making precise focusing challenging for inexperienced users; the LED’s spectral width, while acceptable for most wave‑optics demonstrations, is insufficient for high‑precision interferometry that would benefit from laser coherence; and maintaining the exact 160 mm tube‑lens‑to‑objective spacing required by some commercial objectives is difficult without precision machining, which the authors circumvent by selecting infinity‑corrected objectives with longer working distances.

In summary, the authors deliver a practical, cost‑effective, and pedagogically rich microscope platform that integrates modern 3D‑printing with readily available optics. It enables students to experience the full lifecycle of an optical instrument—from mechanical design and alignment to quantitative measurement of fundamental wave phenomena—thereby strengthening conceptual understanding and hands‑on competence in modern optics.