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AIP Advances

Coherent population trapping resonance characteristics of near pure coherent bichromatic light achieved through injection locking

Suping Qu, Yi Yin

Published Jul 1, 2026• 0 citations
Publisher

Abstract

A lin⊥lin quasi-bichromatic light can be employed to realize a double-Λ coherent population trapping (CPT) resonance configuration, thereby enabling a CPT atomic clock with improved performance. A method for generating such light is proposed, in which two lasers with different linewidths are used to achieve a microwave frequency separation of several gigahertz. The effects of the optical injection ratio from the master extended-cavity diode laser into the slave vertical-cavity surface-emitting laser and the microwave power modulating the slave laser on the locking range were systematically investigated. The influence of both the injection ratio and microwave power on the contrast, linewidth, and the ratio of contrast to linewidth of the CPT signal is also studied. To enhance the trapping efficiency, single-pass and multi-pass interactions between the lin⊥lin quasi-bichromatic light and 87Rb atoms are investigated, with near-purely coherent states achieved under multi-pass interactions. Our scheme offers a promising solution for high-performance atomic clock applications.

DOI
10.1063/5.0336834

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A lin⊥lin quasi-bichromatic light can be employed to realize a double-Λ coherent population trapping (CPT) resonance configuration, thereby enabling a CPT atomic clock with improved performance. A method for generating such light is proposed, in which two lasers with different linewidths are used to achieve a microwave frequency separation of several gigahertz. The effects of the optical injection ratio from the master extended-cavity diode laser into the slave vertical-cavity surface-emitting laser and the microwave power modulating the slave laser on the locking range were systematically investigated. The influence of both the injection ratio and microwave power on the contrast, linewidth, and the ratio of contrast to linewidth of the CPT signal is also studied. To enhance the trapping efficiency, single-pass and multi-pass interactions between the lin⊥lin quasi-bichromatic light and 87Rb atoms are investigated, with near-purely coherent states achieved under multi-pass interactions. Our scheme offers a promising solution for high-performance atomic clock applications.
With two vertical-cavity surface-emitting lasers working under the master-slave sideband injection-locking configuration, we have realized a quasi-bichromatic laser beam with residual phase noise Δφ(2) < 0.282 rad(2). The two wanted frequency components share more than 96% power of the beam. With the realized beam, we have carried out coherent population trapping (CPT) resonance experiment with (87)Rb in the lin[perpendicular]lin CPT scheme, and recorded CPT resonance signal with contrast of 60%. Such laser system is promising to realize a lin[perpendicular]lin CPT clock with high performance and low power consumption.
Abstract The coherent population trapping (CPT) atomic clock is very promising for use in next-generation spaceborne applications owing to its compactness and high performance. In this paper, we propose and implement a CPT atomic clock based on the direct modulation of a large-modulation-bandwidth and narrow-linewidth distributed Bragg reflector laser, which replaces the usually used external bulk modulator in high-performance CPT clocks. Our method retains the high performance while significantly reducing the clock size. Using this highly compact bichromatic light source and simplest CPT configuration, in which a circularly polarized bichromatic laser interrogates the 87 Rb atom system, a CPT signal of clock transition with a narrow linewidth and high contrast is observed. We then lock the local oscillator frequency to the CPT resonance and demonstrate an encouraging short-term frequency stability of 3.6 × 10 −13 τ −1/2 (4 s ⩽ τ ⩽ 200 s). We attribute it to the ultralow laser frequency and intensity noise as well as to the high-quality-factor CPT signal. This study can pave the way for the development of compact high-performance CPT clocks based on our scheme.
Previously, we have proposed a method to control the emission spectrum of the vertical-cavity surface-emitting laser (VCSEL) with the synchronized modulation of the injection current at single and doubled frequencies. In this work, the above method is used to improve the metrological characteristics of the coherent population trapping (CPT) resonance in 87 Rb. The dual-frequency (DF) modulation reduces the carrier power and suppresses the light shift of the resonance frequency, if it is unattainable with the single-frequency modulation. In addition, a higher resonance contrast is achieved by equalizing the powers of the resonant components of the spectrum.
We present a microwave frequency standard based on coherent population trapping (CPT) in the 87Rb D1 line. The CPT spectrum is obtained using two Raman lasers with a 6.8 GHz frequency offset by injection locking of a master laser to a slave laser. We have constructed an atomic clock employing a 5 cm long Rb vapor cell confined with 6.67 kPa neon buffer gas at 70 °C. Using this system, we improve the CPT contrast through the elimination of undesired off-resonant fields created by the direct modulation method. We measured the frequency shift of the CPT signal as a function of the temperature of the Rb cell and estimated it to be approximately 1.3 ×10−9/K. The frequency of a 10 MHz crystal oscillator has been stabilized to the CPT spectrum between the two ground states in 87Rb. The relative frequency stability is approximately 2.3×10−12 for an average time of 68 s.
Coherent population trapping (CPT) atomic clocks are prevailingly realized by exciting CPT resonance with circularly polarized bichromatic coherent light (σ+-σ+ scheme), while atom utilization efficiency is relatively low in the scheme. For improving efficiency, we experimentally study the scheme of realizing CPT resonance through the interaction between atoms and parallel linearly polarized bichromatic coherent light field (lin//lin scheme). In the same experimental conditions the experimental results show that the signal-noise ratio of the CPT resonance signal is twice, and the differential slope is 1.65 time higher than those of σ+-σ+ scheme. The experimental results reveal that the scheme is an ideal candidate for low power consuming atomic clock and magnetometer.
We present a chip scale lin⊥lin quasi-bichromatic laser beam generator scheme and our experimental study results. Through modulating two vertical-cavity surface-emitting lasers (VCSELs) with the same microwave, both VCSELs output multichromatic lasers and every frequency component in their outputs contributes for the frequency mutual injection locking between VCSELs. The system outputs a lin⊥lin quasi-bichromatic laser beam in which the two wanted frequency components share more than 90% of the total laser power. It is promising to apply the chip device in the chip scale coherent population trapping (CPT) atomic clock and the chip scale CPT magnetometer.