A portable LED-based diamond magnetometer for outreach and teaching labs

TL;DR

The study addresses the need for safe, accessible demonstrations of NV center magnetometry in teaching labs by replacing laser excitation with a high-power LED. It presents a compact, LED-driven cw-ODMR magnetometer that uses a prism-mixing rod optical path, a printed single-turn MW loop, and a Red Pitaya for lock-in detection, achieving ODMR spectra and a sensitivity around $1~\mu\mathrm{T}/\sqrt{\mathrm{Hz}}$. The authors provide construction details, cost estimates (about $4500), and supplementary materials with CAD files and example data to support uptake in outreach and undergraduate laboratories. This work enables hands-on exploration of spin physics, Zeeman splitting, and magnetometry in safe, visually engaging demonstrations with practical instructional value.

Abstract

We present a compact, low-cost version of an NV center diamond magnetometer which replaces the standard green laser with a high-power LED. This modification improves safety, reduces cost, and allows the green excitation and red photoluminescence to be viewed directly during demonstrations. The device is simple to assemble and suitable for outreach activities and undergraduate laboratories. We show that it can produce ODMR spectra and respond to nearby magnetic objects, with a sensitivity on the order of 1 $μ$T/$\sqrt{\text{Hz}}$. Supplementary material provides details of the construction and suggestions for student investigations to support use in teaching laboratories.

Figures (7)

• Figure 1: (Left) Schematic of the experiment. The gray squares denote the two block magnets attached to the circuit board and the pink square denotes the NV diamond. (Right) Schematic of the prism and diamond placement (not to scale). The bottom rectangle denotes the circuit board and the rectangle between the prism and the circuit board is the NV diamond placed on top of a thin metal pad. The gap between the prism and the light mixing rod is exaggerated to indicate that a filter is placed in between.
• Figure 2: Excerpt of the top copper Gerber layer of the printed circuit board showing the integrated microwave loop used for ODMR. The circular pad on the right connects to the SMA input. A straight copper trace routes the microwave signal to the printed single-turn loop in the middle of the board, which generates the oscillating magnetic field to drive the NV spin transitions. The diamond sits directly above this loop during operation. Full PCB design files are provided in the Supplementary Material.
• Figure 3: Measured ODMR spectrum from the LED-excited diamond magnetometer, acquired using the same operating settings as the demonstration in Fig. 5. The dashed line marks the working point, defined as the frequency at which the ODMR amplitude exhibits its maximum slope $dV/df$.
• Figure 4: Photo of the demonstration setup.
• Figure 5: Time series of the demodulated PL signal when a steel Allen key is moved close to the magnetometer. The in-phase (“demod-X”) channel exhibits a spike, whereas the quadrature (“demod-Y”) channel remains near zero as expected for correctly phased lock-in detection. This measurement was performed using the LED magnetometer in its standard demonstration configuration.