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Science Advances

Dual-media laser system: Nitrogen vacancy diamond and red semiconductor laser

Lukas Lindner, Felix A. Hahl, Tingpeng Luo, Guillermo Nava Antonio, Xavier Vidal, Marcel Rattunde, Takeshi Ohshima, Joachim Sacher, Qiang Sun, Marco Capelli, Brant C. Gibson, Andrew D. Greentree, Rüdiger Quay, Jan Jeske

Published Sep 27, 2024• 12 citations
Publisher

Abstract

Diamond is a potential host material for laser applications due to its exceptional thermal properties, ultrawide bandgap, and color centers, which promise gain across the visible spectrum. More recently, coherent laser methods offer improved sensitivity for magnetometry. However, diamond fabrication is difficult in comparison to other crystalline matrices, and many optical loss channels are not yet understood. Here, we demonstrate a continuous-wave laser threshold as a function of the pump intensity on nitrogen-vacancy (NV) color centers. To achieve this, we constructed a laser cavity with both an NV diamond medium and an intracavity antireflection-coated diode laser. This dual-medium approach compensates intrinsic losses of the cavity by providing a fixed additional gain below threshold of the diode laser. We observe a continuous-wave laser threshold of the laser system and linewidth narrowing with increasing green pump power on the NV centers. Our results are a major development toward coherent approaches to magnetometry.

DOI
10.1126/sciadv.adj3933

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Diamond is a potential host material for laser applications due to its exceptional thermal properties, ultrawide bandgap, and color centers, which promise gain across the visible spectrum. More recently, coherent laser methods offer improved sensitivity for magnetometry. However, diamond fabrication is difficult in comparison to other crystalline matrices, and many optical loss channels are not yet understood. Here, we demonstrate a continuous-wave laser threshold as a function of the pump intensity on nitrogen-vacancy (NV) color centers. To achieve this, we constructed a laser cavity with both an NV diamond medium and an intracavity antireflection-coated diode laser. This dual-medium approach compensates intrinsic losses of the cavity by providing a fixed additional gain below threshold of the diode laser. We observe a continuous-wave laser threshold of the laser system and linewidth narrowing with increasing green pump power on the NV centers. Our results are a major development toward coherent approaches to magnetometry.
Diamond has long been identified as a potential host material for laser applications. This potential arises due to its exceptional thermal properties, ultra-wide bandgap, and color centers which promise gain across the visible spectrum. More recently, coherent laser methods offer new approaches to magnetometry. However, diamond fabrication is difficult in comparison to other crystalline matrices, and many optical loss channels are not yet understood. Here, we demonstrate the first continuous-wave nitrogen-vacancy (NV) color center laser system. To achieve this, we constructed a laser cavity with both, an NV-diamond medium and an intra-cavity anti-reflection coated diode laser. This dual-medium approach compensates intrinsic losses of the cavity by providing a fixed additional gain below threshold of the diode laser. We observe the first clear continuous-wave laser threshold in the output of the laser system as well as linewidth narrowing with increasing green pump power on the NV centers. Our results are a major development towards coherent approaches to magnetometry.
Nitrogen-vacancy centers (NV) in diamond are promising quantum systems for magnetic field sensing. The sensitivity and the linearity of such a quantum sensor can be greatly improved by using stimulated emission of the NV centers in the concept of laser threshold magnetometry (LTM), which is projected to reach the fT/sqrt(Hz) regime. Previous implementations of NV centers in optical cavities relied on external seed lasers, pulsed operation, or sensing via NVabsorption. In our work, we combine the NV centers with a second gain medium, a laser diode, within the same cavity, achieving self-sustainable continuous-wave lasing. This approach compensates the intrinsic losses of the cavity and the diamond, through a fixed additional gain below the threshold of the laser system. A continuous-wave laser threshold and a linewidth narrowing is observed with increasing pump power on the NV centers of the combined laser system. An improved laser system shows a magnetic field-dependent laser threshold, which is the basis for improved-sensitivity NV magnetometry via LTM.
Nitrogen-vacancy (NV) centers in diamond are a promising platform for high-precision magnetometry. In contrast to the use of spontaneous emission in a number of NV-magnetometers, laser threshold magnetometry exploits stimulated emission of NV centers by placing an NV-doped diamond inside an optical cavity. The NV laser system is predicted to reach a high magnetic-field-dependent contrast and coherent signal strength, leading to an improved magnetic field sensitivity combined with high linearity. Here, we consider a two-media setup where the cavity additionally includes a vertical external cavity surface emitting a laser. This optically active material compensates cavity losses at 750 nm while still allowing for magnetic-field-dependent effects from the NV-diamond. We demonstrate a magnetic-field-dependent laser threshold and investigate the effects of pump laser induced absorption of the diamond. The experimental data are supported by an analytical simulation based on a rate model. Furthermore, we derive a generalized formula to compute the shot-noise-limited magnetic field sensitivity in the regime of high contrast, yielding 49.07(0.33)pT/Hz for the present setup. Simulations with an optimized NV-diamond suggest that values down to 4.9fT/Hz are possible.
Nitrogen vacancy (NV) centers in diamond have attracted considerable recent interest for use in quantum sensing, promising increased sensitivity for applications ranging from geophysics to biomedicine. Conventional sensing schemes involve monitoring the change in red fluorescence from the NV center under green laser and microwave illumination. Due to the strong fluorescence background from emission in the NV triplet state and low relative contrast of any change in output, sensitivity is severely restricted by a high optical shot noise level. Here, we propose a means to avoid this issue, by using the change in green pump absorption through the diamond as part of a semiconductor external cavity laser run close to the lasing threshold. We show that theoretical sensitivity to the magnetic field on the pT/Hz\sqrt{\mathrm{Hz}}Hz​ level is possible using a diamond with an optimal density of NV centers. We discuss the physical requirements and limitations of the method, particularly the role of amplified spontaneous emission near threshold and explore realistic implementations using current technology.
Nitrogen-vacancy (NV) centers in diamond can be used as a highly sensitive sensor for magnetic fields. One concept to reach the fT/sqrt(Hz) regime is laser threshold magnetometry (LTM). In this talk, we present a self-sustainable, magnetic field-dependent cw NV laser system. To achieve this, we place the NV-diamond within the external cavity of a red VECSEL. When the NV-diamond is pumped, we observe a decrease of the pump power at laser threshold of the VECSEL while the cavity output increases by up to 10%. We demonstrate a strong magnetic-field dependence of the laser threshold as a function of the VECSEL pump power. Our results demonstrate a practical concept for self-sustainable LTM devices based on NV-gain.
High precision magnetometry is important for a range of applications from the monitoring of biologically generated magnetic fields (e.g. magnetoencephalography and magnetocardiography), to navigation in GPS denied environments, to the detection of gravitational waves. Diamond containing the negatively-charged nitrogen vacancy colour centre (NV-) has emerged as a powerful room-temperature sensing solution. Here we explore NV- centres as a laser medium for a new form of magnetometry: laser threshold magnetometry (LTM). LTM works by placing NV- inside an optical cavity and uses the coherent laser output as a potentially more sensitive readout channel than is possible using conventional (incoherent) optically detected magnetic resonance. Here we show progress towards LTM with diamond. We show twolaser excitation and stimulated emission in free space, and report progress towards diamond-cavity experiments. Our studies highlight the need for different NV- optimisation for laser applications, rather than those conventionally used for quantum information applications