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Optics Express

High-power injection-locked blue laser for Rydberg atom-based sensing

Xiaoliang Zuo, Qingbin Li, Danyang Li, Haiteng Wu, Jiteng Sheng, Haihua Wu

Published Jun 17, 2025• 3 citations
Publisher

Abstract

A compact, high-power, and stable blue laser source is essential for Rydberg state excitation of rubidium (Rb) atoms, particularly for emerging Rydberg atom-based sensors that require portability for practical applications. In this work, we present an injection-locked laser system using blue laser diodes for both the leader and follower lasers near 480 nm, enabling efficient Rydberg state preparation of Rb and eliminating the need for nonlinear frequency-doubling. The locked follower laser delivers 263 mW of output power with a linewidth of 591(31) kHz after frequency stabilization. High-efficiency spatial mode matching between the seed light and follower laser is accomplished through a polarization-maintaining fiber, resulting in a power gain of 30.4 dB. The compact optical path design allows the laser system to occupy just 20 × 21 × 4 cm 3 . Such a high-power and compact injection-locked blue laser system provides a low-cost and efficient solution for Rydberg atom-based applications.

DOI
10.1364/oe.559932

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A compact, high-power, and stable blue laser source is essential for Rydberg state excitation of rubidium (Rb) atoms, particularly for emerging Rydberg atom-based sensors that require portability for practical applications. In this work, we present an injection-locked laser system using blue laser diodes for both the leader and follower lasers near 480 nm, enabling efficient Rydberg state preparation of Rb and eliminating the need for nonlinear frequency-doubling. The locked follower laser delivers 263 mW of output power with a linewidth of 591(31) kHz after frequency stabilization. High-efficiency spatial mode matching between the seed light and follower laser is accomplished through a polarization-maintaining fiber, resulting in a power gain of 30.4 dB. The compact optical path design allows the laser system to occupy just 20 × 21 × 4 cm 3 . Such a high-power and compact injection-locked blue laser system provides a low-cost and efficient solution for Rydberg atom-based applications.
Using modulation transfer spectroscopy, we achieve the frequency stabilization of a high-power 3-W blue laser at the wavelength of 420 nm to the Rb\mathrm{Rb}Rb 5S1/25{S}_{1/2}5S1/2​--6P3/26{P}_{3/2}6P3/2​ transition. The in-loop frequency stability of this laser is $1.8\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}11}/\sqrt{\ensuremath{\tau}}$, reaching $1.7\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}12}$ at 100 s and $7\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}13}$ at 1000 s. An external power feedback loop is established using an acousto-optic modulator, employing the zeroth-order diffracted light for power stabilization, achieving an in-loop power stability of $1.0\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}6}$ at 1 s. Moreover, the continuous mode-hop free interval of this high-power laser can simultaneously cover the 5S1/25{S}_{1/2}5S1/2​--6P3/26{P}_{3/2}6P3/2​ transitions of 85Rb{}^{85}\text{Rb}85Rb and 87Rb{}^{87}\text{Rb}87Rb, with successful locking achieved for both isotopes, providing a comprehensive analysis of the Rb\mathrm{Rb}Rb atomic transitions in the blue spectral region. As an application, this 3-W 420-nm laser with excellent power and frequency stabilities is used as a repumping source for diffuse laser cooling of 87Rb{}^{87}\text{Rb}87Rb atoms, realizing a one-meter-long cold-atom cloud. This paves the way for using blue-light cooling to realize a cold-Rb\mathrm{Rb}Rb-atom active optical clock. In addition, the ultrahigh-stability 420-nm laser also finds applications in various fields such as the Rydberg atom experiment, Bose-Einstein condensation, ultranarrow-bandwidth Faraday atomic filter, and so on.
Abstract The realization of compact high-power narrow-linewidth laser sources in the visible range has been a long-standing interest for the atomic physics community, especially in the field of laser cooling and trapping of alkaline-earth and alkaline-earth-like atoms. We report a simple master-slave injection-locked laser system capable of generating 500 mW at 460.86 nm with a linewidth of 1.6 MHz to realize magneto-optical trapping of strontium atoms on the 5s2 1S0−5s5p 1P15s^{2} \ ^{1}\mathrm {S}_{0}-5s5p \ ^{1}\mathrm {P}_{1}5s2 1S0​−5s5p 1P1​ 5 s 2 1 S 0 - 5 s 5 p 1 P 1 transition. The master laser used is an external cavity diode laser built with an anti-reflection coated laser diode in a Littrow configuration and the slave laser is built with a recently launched single mode high power GaN laser diode. We characterized the frequency noise, injection stability, spectral purity and relative intensity noise of the laser system. The reported laser system is used routinely to produce 10710^7107 10 7 strontium atoms at a temperature of 10 mK in a magneto-optical trap. The laser system offers a prominent alternative to the existing frequency-doubled laser systems in terms of cost, design flexibility, electrical power consumption, ease of scaling, intensity stability, and frequency tunability. The proposed system is also an effective solution for space-based experiments where a laser system’s size, weight, and electrical power consumption are crucial design parameters.
Creating a quantum computer requires a system of particles that can be well-controlled to achieve quantum operations. We need a large array of these particles – called qubits – with long coherence times, which can be initialized, operated on by single and two qubit gates, and read out. For neutral atoms, the qubit states are stable ground states that interact minimally with the environment, leading to long coherence times. Experimentally, the qubits are manipulated using carefully timed laser beam pulses with controlled frequency and intensity, but the outstanding issue for optically trapping cold atoms is finding a light pattern that can hold an array of individually addressable atoms to perform these quantum operations. To solve this, pinhole diffraction patterns were previously computationally analyzed to trap a 2D array of qubits within localized bright and dark spots. This project implements an injection locked laser into this system to provide a high power, tunable light source for the pinhole diffraction pattern atomic trap. In this project, the injection locked laser system is tuned to and analyzed at 780 nm to observe the locking efficiency as a function of the laser diode temperature or current supplied to the tuned-frequency laser diode, also known as the seed laser. Data taken on the injection lock efficiency over varying seed laser power in the system, current supplied to the seed laser diode, and laser diode temperature confirm that there is a large dependence upon each of these settings. An optimal combination of seed laser diode temperature and current supplied to it can be found to provide an efficient and stable power source for the atomic trap.
We propose and demonstrate an alternative method for spectral filtering and frequency stabilization of both 780-nm and 960-nm lasers using a high-finesse length-tunable cavity (HFLTC). Firstly, the length of HFLTC is stabilized to a commercial frequency reference. Then, the two lasers are locked to this HFLTC using the Pound–Drever–Hall (PDH) method which can narrow the linewidths and stabilize the frequencies of both lasers simultaneously. Finally, the transmitted lasers of HFLTC with each power up to about 100 μW, which act as seed lasers, are amplified using the injection locking method for single-atom Rydberg excitation. The linewidths of obtained lasers are narrowed to be less than 1 kHz, meanwhile the obtained lasers’ phase noise around 750 kHz are suppressed about 30 dB. With the spectrally filtered lasers, we demonstrate a Rabi oscillation between the ground state and Rydberg state of single-atoms in an optical trap tweezer with a decay time of (67 ± 37) μs, which is almost not affected by laser phase noise. We found that the maximum short-term laser frequency fluctuation of a single excitation lasers is at ∼3.3 kHz and the maximum long-term laser frequency drift of a single laser is ∼46 kHz during one month. Our work develops a stable and repeatable method to provide multiple laser sources of ultra-low phase noise, narrow linewidth, and excellent frequency stability, which is essential for high precision atomic experiments, such as neutral atom quantum computing, quantum simulation, quantum metrology, and so on.
A free-running, temperature stabilized diode laser has been injection-locked to an external cavity diode laser for use in cold Rydberg atom experiments. Cold rubidium atoms in a magneto-optical trap (MOT) are excited to Rydberg states using a 10 ns laser pulse. The Rydberg atoms spontaneously ionize due to dipole forces, and the collisional ionization dynamics are observed as a function of atom density and principal quantum number of the Rydberg state, n. The injection-locked diode laser will be used as a repumper in conjunction with a dark spontaneous-force optical trap (SPOT) to increase the Rydberg state density. We report on the design of the injection-locked laser system.