Development of a Modular ODMR Setup for Optical Experiments in a Variable Temperature Insert

TL;DR

This work addresses the challenge of performing NV-center ODMR magnetometry inside standard helium bath cryostats with variable temperature inserts by delivering a modular, cryo-compatible optical geometry. The authors present an external optical head, a long, integrated sample stick with microwave delivery, and a rail-guided alignment platform to preserve optical quality over nearly two meters. They demonstrate temperature- and magnetic-field-dependent ODMR in a bulk diamond and detect a ferromagnetic transition in SrRuO3, validating the method and illustrating compatibility with high-pressure environments. The results establish a practical blueprint for deploying high-stability NV magnetometry in constrained cryogenic setups, enabling nanoscale magnetic sensing in materials under extreme conditions and guiding future implementations in diamond anvil cells.

Abstract

We developed an optically detected magnetic resonance (ODMR) setup designed for compatibility with a widely used, commercially available helium bath cryostat equipped with a variable temperature insert. The optical path extends nearly two meters, spanning the full length of the cryostat insert, enabling excitation of the nitrogen-vacancy (NV) centers and detection of the resulting fluorescence from outside the cryostat. The setup preserves optical alignment and beam quality along this extended path allowing integration into existing cryogenic systems without significant modifications. We demonstrate the setup's performance by measuring the temperature dependence of the resonance signal and its behavior under small applied magnetic fields, as well as the magnetic transition of a SrRuO$_3$ sample, thereby showcasing the feasibility of NV magnetometry on a sample in constrained cryogenic environments.

Figures (16)

• Figure 1: Schematic of the optical components and their arrangement. The components are labeled and listed in the legend above. The schematic shows the light path of the excitation laser as well as the path of the collected fluorescence.
• Figure 2: (a) CAD assembly of the sample stick and its support structure used for optical alignment at room temperature prior to installation in the cryostat. Key dimensions and features are indicated. (b) Photograph of the assembled sample stick with support structure for comparison. (A) Optical head and sample stick for the VTI (B) in its support frame for room-temperature storage and testing (C) and (D) shows the sample stick sample cage with detailed view in the following figure.
• Figure 3: Detailed view of the sample holder at the lower end of the sample stick, showing the objective (E), the temperature sensor (F), a diamond chip mounted on a coplanar waveguide (G), the sample holder (H), and the piezo actuator at the base (I). Specific details may be found in the table above.
• Figure 4: (a) CAD model of the modular aluminum support table with a rail-guided platform (K), designed for reproducible positioning of the optical head (J) above the sample stick (L) mounted in the cryostat (M). The sliding platform ensures precise and repeatable alignment. Key structural features and dimensions are annotated. (b) Photograph of the assembled support table with the optical head mounted on the sliding platform for comparison.
• Figure 5: Schematic diagram of the measurement electronics used for optically detected magnetic resonance (ODMR) measurements of the NV centers. The diagram illustrates the connections between components, with emphasis on the different trigger signals required for pulsed measurement mode, generated by a synchronous digital pattern and arbitrary waveform generator. Specific details on the devices may be found in the legend above.