Saturable absorption in NV-doped diamond studied by femtosecond Z-scan

TL;DR

This study explores the nonlinear optical absorption properties of NV-doped diamond using femtosecond Z-scan measurements, revealing the significant influence of complex defect interactions on saturation behavior.

Contribution

It demonstrates that the nonlinear absorption in NV-doped diamond results from combined effects of NV centers and H2 defect complexes, not just NV centers alone.

Findings

NV-doped diamond exhibits pronounced saturable absorption.

The saturation response involves both NV centers and H2 defect complexes.

For highly doped samples, the saturation intensity is 40 GW/cm².

Abstract

We investigate nonlinear optical absorption in diamond crystals containing high densities of nitrogen vacancy (NV) centers using open-aperture Z-scan measurements with 230 fs laser pulses at 1032 nm, within the transparency window of diamond. While high-purity electronic-grade diamond exhibits third-order nonlinear absorption, NV-doped samples display pronounced saturable absorption that strengthens with increasing defect concentration. Linear transmission spectroscopy reveals that, in addition to NV centers, the crystals host significant populations of H2 (NVN-) defect complexes whose absorption band partially overlaps the excitation wavelength. By correlating spectroscopic data with nonlinear measurements and modeling the response using an effective two-level system, we show that the observed saturation cannot be attributed solely to NV centers but arises from the combined contribution of NV-related and H2 defects. For the highly doped sample, we determine an effective linear absorption coefficient of alpha0 = 6.52 cm-1 and a saturation intensity of Is = 40.0 GW/cm2. These findings highlight the critical role of the complex defect landscape in governing the nonlinear optical response of NV-doped diamond and underscore the necessity of accounting for ancillary defect species in the design of diamond-based nonlinear and quantum photonic devices.