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arXiv:2206.00096 · Optics Express

Intra-cavity frequency-doubled VECSEL system for narrow linewidth Rydberg EIT spectroscopy

Joshua C. Hill, William K. Holland, Paul D. Kunz, Kevin C. Cox, Jussi-Pekka Penttinen, Emmi L. Kantola, David H. Meyer

Published Oct 7, 2022• 15 citations
arXivHTMLPDF

Abstract

High-power, narrow-linewidth light sources in the visible and UV spectra are in growing demand, particularly as quantum information and sensing research proliferates. Vertical external-cavity surface-emitting lasers (VECSELs) with intra-cavity frequency conversion are emerging as an attractive platform to fill these needs. Using such a device, we demonstrate 3.5 MHz full-width half-maximum Rydberg-state spectroscopy via electromagnetically induced transparency (EIT). The laser's 690 mW of output power at a wavelength of 475 nm enables large Rabi frequencies and strong signal-to-noise ratio in shorter measurement times. In addition, we characterize the frequency stability of the VECSEL using the delayed self-heterodyne technique and direct comparison with a commercial external-cavity diode laser (ECDL). We measure the pre-doubled light's Lorentzian linewidth to be 2π × 5.3(2) kHz, and the total linewidth to be 2π × 23(2) kHz. These measurements provide evidence that intra-cavity frequency-doubled VECSELs can perform precision spectroscopy at and below the MHz level, and are a promising tool for contemporary, and future, quantum technologies.

DOI
10.1364/oe.473676

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High-power, narrow-linewidth light sources in the visible and UV spectra are in growing demand, particularly as quantum information and sensing research proliferates. Vertical external-cavity surface-emitting lasers (VECSELs) with intra-cavity frequency conversion are emerging as an attractive platform to fill these needs. Using such a device, we demonstrate 3.5 MHz full-width half-maximum Rydberg-state spectroscopy via electromagnetically induced transparency (EIT). The laser's 690 mW of output power at a wavelength of 475 nm enables large Rabi frequencies and strong signal-to-noise ratio in shorter measurement times. In addition, we characterize the frequency stability of the VECSEL using the delayed self-heterodyne technique and direct comparison with a commercial external-cavity diode laser (ECDL). We measure the pre-doubled light's Lorentzian linewidth to be 2π × 5.3(2) kHz, and the total linewidth to be 2π × 23(2) kHz. These measurements provide evidence that intra-cavity frequency-doubled VECSELs can perform precision spectroscopy at and below the MHz level, and are a promising tool for contemporary, and future, quantum technologies.
We report low noise and narrow linewidth performance of an actively stabilized optical parametric oscillator, intracavity-pumped by a visible AlGaInP-based vertical-external-cavity surface-emitting laser (VECSEL). Under dual-locking conditions, where the VECSEL and intracavity resonant idler are stabilized using the Pound–Drever–Hall and side-of-fringe locking techniques, respectively, narrow linewidths of 6.21(1) kHz (VECSEL) and 151(1) Hz (idler) are achieved for integration times as long as 4 s, illustrating the transfer of noise from the VECSEL fundamental to the OPO non-resonant signal. In this regime, the relative intensity noise of all three interacting waves is <−120 dBc/Hz for all frequencies above 1 kHz, indicating that this coherent laser system is well-suited for quantum optics experiments, potentially those involving squeezed light generation.
Experiments in atomic, molecular, and optical (AMO) physics rely on lasers at many different wavelengths and with varying requirements on spectral linewidth, power, and intensity stability. Vertical external-cavity surface-emitting lasers (VECSELs), when combined with nonlinear frequency conversion, can potentially replace many of the laser systems currently in use. Here we present and characterize VECSEL systems that can perform all laser-based tasks for quantum information processing experiments with trapped magnesium ions. For photoionization of neutral magnesium, 570.6 \,nm light is generated with an intracavity frequency-doubled VECSEL containing a lithium triborate (LBO) crystal for second harmonic generation. External frequency doubling produces 285.3 \,nm light for resonant interaction with the 1S0↔^{1}S_{0}\leftrightarrow1S0​↔ 1P1^{1}P_{1}1P1​ transition of neutral Mg. Using an externally frequency-quadrupled VECSEL, we implement Doppler cooling of 25^{25}25Mg+^{+}+ on the 279.6 \,nm 2S1/2↔^{2}S_{1/2}\leftrightarrow2S1/2​↔ 2P3/2^{2}P_{3/2}2P3/2​ cycling transition, repumping on the 280.4 \,nm 2S1/2↔^{2}S_{1/2}\leftrightarrow2S1/2​↔ 2P1/2^{2}P_{1/2}2P1/2​ transition, coherent state manipulation, and resolved sideband cooling close to the motional ground state. Our systems serve as prototypes for applications in AMO requiring single-frequency, power-scalable laser sources at multiple wavelengths.
Electromagnetically Induced Transparency detection of high-lying Rydberg states in room-temperature rubidium vapor was investigated using a four state ladder-type excitation scheme with light provided by three External Cavity Diode Lasers (ECDLs) at 780 nm, 776 nm, and 1266 nm. This detection technique was studied by characterizing the lineshape parameters of the EIT transmission peak, specifically the height, width and area of the transparency window as functions of the dressing and coupling laser powers. With the goal of characterizing the linewidth of the transmission signal, a confocal etalon was built and implemented in the optical setup to perform frequency calibration of the EIT spectra. Our experimental results indicate that the EIT transmission peak exhibits a non-monotonic dependence on laser power as we observed that the signal initially increases in amplitude, reaches a maximum value and then decays gradually at higher powers. We also observed power broadening of the linewidth at low dressing powers with constant coupling power, and saturation of the broadening in the middle to high dressing power regime. The EIT linewidth was observed to be approximately constant with varying coupling power in the power regimes studied in this experiment.
The spectra of Rydberg atoms are of great significance for studying the energy levels of Rydberg atoms and the interaction between neutral atoms, especially, the high-precision spectra of Rydberg atoms can be used to measure the energy level shifts of Rydberg atoms resulting from the dipole-dipole interactions in room-temperature vapor cells. In this paper we report the preparation of cesium Rydberg states based on the cascaded two-photon excitation of 509 nm laser and 852 nm laser in opposite, and the measurements of the fine structure of cesium Rydberg states. In this experiment, the 509 nm laser is generated by the cavity-enhanced second-harmonic generation from 1018 nm laser with a periodically-poled KTP crystal and has a maximum power of about 1 W, and the 852 nm probe laser is provided by an external-cavity diode laser with a maximum output power of 5 mW and a typical linewidth of 1 MHz. By scanning the frequency of 509 nm coupling laser, it is presented that the Doppler-free spectra based on electromagnetically-induced transparency (EIT) of 509 nm coupling laser and 852 nm probe laser. The velocity-selective EIT spectra are used to study the spectral splitting of 6S1/26P3/257S(D) ladder-type system of cesium Rydberg atoms in a room-temperature vapor cell. The powers of 852 nm probe laser and 509 nm coupling laser are 0.3 upW and 200 mW, respectively. Their waist radii are both approximately 50 m. The intervals of hyperfine splitting of the intermediate state 6P3/2(F'=3, 4, 5) and fine splitting of 57D3/2 and 57D5/2 Rydberg states are measured by a frequency calibrating. Concretely, the velocity-selective spectrum with a radio frequency (RF) modulation of 30 MHz is used as a reference to calibrate the Rydberg fine-structure states in the hot vapor cell, where the RF frequency precision is smaller than a hertz on long time scales and the EIT linewidth is smaller than 13 MHz. The experimental value of the fine structure splitting of 57D3/2 and 57D5/2 Rydberg states is (354.72.5) MHz, that is in consistence with the value of 346.8 MHz calculated by Rydberg-Ritz equation and quantum defects of 57D3/2 and 57D5/2 Rydberg states. The experimental values of hyperfine splitting of intermediate state 6P3/2(F'=3, 4, 5) are also coincident with the theoretical calculated values. The dominant discrepancy existing between the experimental and calculated results may arise from the nonlinear correspondence of the PZT while the 509 nm wavelength cavity is scanned, and the measurement accuracy influenced by the spectral linewidth. The velocity-selective spectroscopy technique can also be used to measure the energy level shifts caused by the interactions of Rydberg atoms.
Spectroscopy of Rydberg states has become a popular platform for quantum sensing, with the most common readout scheme being two-photon electromagnetically induced transparency (EIT) using counterpropagating laser beams. In this scheme, the energy resolution of the Rydberg state is set by the spectral linewidth of the EIT feature. While selection criteria for the two-photon resonance can narrow the linewidth to the order of the Rydberg state decay rate for a single atom, the Doppler shift from thermal velocity of the atoms broadens the ensemble linewidth to the order of the decay rate of the intermediate state. Here, we derive an analytic expression for the Doppler residual line shape in the low-power limit and corroborate the results with experiment. For Rb, we find the full-width-at-half-maximum linewidth limit to be 1.84 MHz when scanning the coupling laser and measure an experimental linewidth of 2.04 MHz. These linewidths are around a factor of 2 narrower than previous theoretical estimates as well as previously reported measured linewidths. With this, we demonstrate the most precise two-photon energy resolution of a Rydberg state in thermal vapor to date. We then map out broadening mechanisms near this limit.