Near-Infrared-Enhanced Charge-State Conversion for Low-Power Optical Nanoscopy with Nitrogen-Vacancy Centers in Diamond

The near-infrared (NIR) photon pumped optical physics of nitrogen-vacancy (NV) centers in diamond is experimentally studied by considering both the charge-state conversion and stimulated emission. We find that the NIR laser can help to highly increase the charge-state conversion rate and, subsequently, can be applied to improve the performance of charge-state-depletion (CSD) nanoscopy. Using a doughnut-shaped visible laser beam and a Gaussian-shaped NIR laser beam for charge-state manipulation, we develop a low-power two-depletion-laser CSD nanoscopy for NV centers. Without dropping the imaging resolution, the visible depletion-laser intensity is approximately 10 times lower than that in the single-depletion-laser CSD. With high spatial resolution and low laser power, the CSD nanoscopy can be used for nanoscale quantum sensing with NV centers.

Figure 1

(a) The level scheme for NV-center charge-state conversion. The transitions of the electron during the two-photon charge-state conversion processes are indicated as ① and ② for the first and second transitions, respectively. STE, stimulated emission; SPE, spontaneous emission; ISC, intersystem crossing. (b) Diagram of the experimental setup. DM1–3 are long-pass dichroic mirrors with edge wavelengths of 605, 536.8, and 658.8 nm, respectively. DM4 is a short-pass dichroic mirror with an edge wavelength of 746 nm. LP is a long-pass filter with an edge wavelength of 668.9 nm. SP is a short-pass filter with an edge wavelength of 761 nm.

Figure 2

(a),(b) The charge-state conversion with visible and NIR laser excitations. The NV center is first initialized by the 532- (a) or 637-nm (b) laser and then pumped by the visible and NIR lasers. Finally, the charge state is detected with a $50\text{−}\mu \mathrm{W}$ 589-nm laser excitation. The solid lines are the exponential fits. (c) The charge-state conversion pumped by the 780- and 637-nm laser pulses with different delays. The duration of the 780- and 637-nm lasers are set to 30 ns, and the pulses repeat $N=400$ cycles. Average power: 637-nm laser, 0.5 mW; 780-nm laser, 5 mW. The fluorescence is normalized to the value with long delay time $\tau$. (d) The charge-state conversion process pumped by the 780- and 532-nm pulsed lasers. Average power: 532-nm laser, 0.06 mW; 780-nm laser, 5 mW. The solid lines are the exponential fits. The fluorescence is normalized to the value with long duration $t$. (e) The fluorescence intensity of the NV centers under coincident excitation with a fixed 532-nm laser and a varied 780-nm laser. The solid line is a guide to the eye. (f) The spin-state Rabi oscillation of ${\mathrm{NV}}^{-}$ measured after 532- and 780-nm laser excitations. The power of the 780-nm laser is indicated in the figure. The 532-nm laser power is fixed at 0.65 mW. The durations of the 532- and 780-nm lasers are 300 ns. The solid lines are the fits to the cosine function. The fluorescence data in (e),(f) are normalized to the signals without the 780-nm laser.

Figure 3

(a) The charge-state conversion rates with the 0.02-mW 532-nm laser and a different 780-nm laser. (b) The 0.8-mW 780-nm acceleration effect changes with 532-nm laser power. The solid lines in (a),(b) are the fits to the model of the charge-state transition rate in Appendix pp1. (c),(d) The steady-state population of the charge state pumped by different lasers. The histograms of the photon counts of a single NV center is measured by the single-shot readout charge-state method. High photon-counting rate presents the ${\mathrm{NV}}^{-}$ charge state. The solid lines are the fits with two Poissonian distributions.

Figure 4

(a) The laser pulse sequence for single-laser- and two-laser-pumping CSD nanoscopy. (b) The schematic of the level transition for CSD nanoscopy. (c),(d) The CSD nanoscopy resolution with different 780- and 532-nm laser pumping. The power of the 532-nm laser in (c) is 0.14 mW. The durations of the depletion lasers are $200\mu \mathrm{s}$. Insert images in (c): Left, image with only the 532-nm depletion-laser beam; right, image with the 532-nm laser and the 2.4-mW 780-nm laser. Inset images in (d): Upper inset, image with 3.9-mW 532-nm depletion laser; lower inset, image with 3.9-mW 532-nm laser and 0.4-mW 780-nm laser. The scale bars of insets in (c),(d) are 200 and 100 nm, respectively.

Figure 5

Illustrations of energy levels and transition rates for ionization-rate analysis.

Figure 6

(a) The laser-pulse sequence for CSD nanoscopy with the 637- and 780-nm depletion lasers. (b) The spatial resolution of CSD nanoscopy changes with the power of the 637-nm doughnut-shaped depletion-laser beam. The power of the 780-nm Gaussian-shaped laser beam is fixed at 2 mW. The duration of the depletion lasers is $200\mu \mathrm{s}$. (c),(d) The images of CSD nanoscopy pumped by the 3.2-mW 637-nm doughnut-shaped laser beam without and with the 2-mW 780-nm Gaussian-shaped laser beam, respectively.