Direct laser micromachining of superconducting terahertz Josephson plasma emitters

TL;DR

This paper presents a rapid, maskless laser micromachining method for fabricating superconducting terahertz Josephson plasma emitters, enabling efficient device production with preserved junctions and versatile electrode options.

Contribution

The study introduces a novel direct ultraviolet laser micromachining technique for superconducting JPEs, demonstrating stable terahertz emission and broad applicability.

Findings

Devices with Cu electrodes perform comparably to Ag electrodes.

Emitted radiation is elliptically polarized and cavity resonance dominated.

Machining width/depth is governed by thermal conductivity, not optical spot size.

Abstract

We demonstrate a rapid, maskless fabrication method for superconducting terahertz Josephson plasma emitters (JPEs) based on direct ultraviolet laser micromachining of Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$ (Bi-2212) single crystals. Although machining debris is formed near the processed regions, uniform stacks of intrinsic Josephson junctions are preserved inside the crystal, enabling stable terahertz emission. Devices fabricated with Ag, Cu, and Cr electrodes all exhibited terahertz radiation, with Cu electrodes showing performance comparable to Ag while offering a low-cost alternative. Spectroscopic and polarization analyses indicate that the emitted radiation is elliptically polarized and dominated by the geometrical cavity resonance mode. Structural and electrical characterizations reveal that the machining width and depth are not limited by the optical spot size but are governed by the anisotropic thermal conductivity of Bi-2212, consistent with a thermally dominated laser ablation process. This direct laser micromachining approach provides a fast and versatile fabrication technique for JPEs and is broadly applicable to superconducting electronics and terahertz devices.