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Communications Physics

An inhibited laser

Tiantian Shi, Duo Pan, Jingbiao Chen

Published Aug 15, 2022• 17 citations
Publisher

Abstract

Abstract Traditional lasers function using resonant cavities, in which the round-trip optical path is equal to an integer multiple of the intracavity wavelengths to constructively enhance the spontaneous emission rate. Taking advantage of the cavity enhancement effect, the narrowest sub-10-mHz-linewidth laser and a 10−16-fractional-frequency-stability superradiant active optical clock (AOC) have been achieved. However, a laser with atomic spontaneous radiation being destructively inhibited in an anti-resonant cavity, where the atomic resonance is exactly between two adjacent cavity resonances, has not been reported. Herein, we experimentally demonstrate the inhibited laser. Compared with traditional AOCs, which exhibit superiority in terms of the high suppression of cavity noise, the suppression of the cavity-pulling effect of an inhibited laser can be further improved by a factor of $${\left(2{{{{{{{\mathcal{F}}}}}}}}/\pi \right)}^{2}$$ 2F/π2 , which is improved from 26 to 53 times. This study will guide further development of AOCs with better stability, and thus, it is significant for quantum metrology and may lead to new research in the laser physics and cavity quantum electrodynamics fields.

DOI
10.1038/s42005-022-00988-y

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An inhibited laser

Tiantian Shi, Duo Pan, Jingbiao Chen

Traditional lasers function using resonant cavities, in which the round-trip optical path is exactly equal to an integer multiple of the intracavity wavelengths to constructively enhance the spontaneous emission rate. By taking advantage of the enhancement from the resonant cavity, the narrowest sub-10-mHz-linewidth laser and a $10^{-16}$-fractional-frequency-stability superradiant active optical clock (AOC) have been achieved. However, a laser with atomic spontaneous radiation being destructively inhibited in an anti-resonant cavity, where the atomic resonance is exactly between two adjacent cavity resonances, has not been reported. Herein, we experimentally demonstrate inhibited stimulated emission and termed it an inhibited laser. Compared with traditional superradiant AOCs, which exhibit superiority in terms of the high suppression of cavity noise, the suppression of the cavity-pulling effect of an inhibited laser can be further improved by a factor of $(2F/pi)^2$, i.e., 2.07 in this work, which was improved from 26 to 53 times. This study will guide further development of AOCs with better stability, and thus, it is significant for quantum metrology and may lead to new research in the laser physics and cavity quantum electrodynamics fields.

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Abstract Traditional lasers function using resonant cavities, in which the round-trip optical path is exactly equal to an integer multiple of the intracavity wavelengths to constructively enhance the spontaneous emission rate. By taking advantage of the resonant cavity enhancement, the narrowest sub-10-mHz-linewidth laser and a 10^-16-fractional-frequency-stability superradiant active optical clock (AOC) have been achieved. However, never has a laser with atomic spontaneous radiation being destructively inhibited in an anti-resonant cavity where the atomic resonance is exactly between two adjacent cavity resonances been proven. Herein, we present the first demonstration of the inhibited stimulated emission, which is termed an inhibited laser. Compared with traditional superradiant AOCs exhibiting superiority for the high suppression of cavity noise in lasers, the effect of cavity pulling on the inhibited laser's frequency can be further suppressed by a factor of (2F/π)^2. This study of the inhibited laser will guide further development of superradiant AOCs with better stability, and may lead to new searches in the cavity quantum electrodynamics (QED) field.

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We have experimentally demonstrated the active optical clock with a good suppression to cavity-length noise compared with the passive one. However, the frequency stability of the four-level active optical clock for thermal atoms is still limited by the residual cavity-pulling effect. In this paper, we preliminarily realized the cavity-length stabilization in 1064/1470 nm dual-wavelength good-bad cavity system. The synchronous cavity-length change between two dual-wavelength systems is realized by using the phase locking technique of 1064 nm goodcavity lasers. Therefore, the beating linewidth of 1470 nm badcavity lasers will also be reduced considering that the 1064/1470 nm dual-wavelength lasers share the one cavity. The tracking accuracy of 1064 nm good-cavity lasers is better than 3×10-16at 1 s after phase-locking, and the linewidth of 1470 nm bad-cavity laser is reduced to 77 Hz. The linewidth of active optical frequency standard is still limited by the light shift, collision shift and Zeeman shift. The beating signal of magnetic sublevels corresponding to the Cs 1470 nm clock transition is observed under Zeeman effect. Further research is needed, such as, the design of vacuum chamber and magnetic shielding, to reduce the linewidth of the continuous 1470 nm active optical frequency standard.

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Abstract Traditional lasers function using resonant cavities, in which the round-trip optical path is equal to an integer multiple of the intracavity wavelengths to constructively enhance the spontaneous emission rate. Taking advantage of the cavity enhancement effect, the narrowest sub-10-mHz-linewidth laser and a 10−16-fractional-frequency-stability superradiant active optical clock (AOC) have been achieved. However, a laser with atomic spontaneous radiation being destructively inhibited in an anti-resonant cavity, where the atomic resonance is exactly between two adjacent cavity resonances, has not been reported. Herein, we experimentally demonstrate the inhibited laser. Compared with traditional AOCs, which exhibit superiority in terms of the high suppression of cavity noise, the suppression of the cavity-pulling effect of an inhibited laser can be further improved by a factor of (2F/π)2{\left(2{{{{{{{\mathcal{F}}}}}}}}/\pi \right)}^{2}(2F/π)2 2F/π2 , which is improved from 26 to 53 times. This study will guide further development of AOCs with better stability, and thus, it is significant for quantum metrology and may lead to new research in the laser physics and cavity quantum electrodynamics fields.
Traditional lasers function using resonant cavities, in which the round-trip optical path is exactly equal to an integer multiple of the intracavity wavelengths to constructively enhance the spontaneous emission rate. By taking advantage of the enhancement from the resonant cavity, the narrowest sub-10-mHz-linewidth laser and a 10−1610^{-16}10−16-fractional-frequency-stability superradiant active optical clock (AOC) have been achieved. However, a laser with atomic spontaneous radiation being destructively inhibited in an anti-resonant cavity, where the atomic resonance is exactly between two adjacent cavity resonances, has not been reported. Herein, we experimentally demonstrate inhibited stimulated emission and termed it an inhibited laser. Compared with traditional superradiant AOCs, which exhibit superiority in terms of the high suppression of cavity noise, the suppression of the cavity-pulling effect of an inhibited laser can be further improved by a factor of (2F/pi)2(2F/pi)^2(2F/pi)2, i.e., 2.07 in this work, which was improved from 26 to 53 times. This study will guide further development of AOCs with better stability, and thus, it is significant for quantum metrology and may lead to new research in the laser physics and cavity quantum electrodynamics fields.
Abstract Traditional lasers function using resonant cavities, in which the round-trip optical path is exactly equal to an integer multiple of the intracavity wavelengths to constructively enhance the spontaneous emission rate. By taking advantage of the resonant cavity enhancement, the narrowest sub-10-mHz-linewidth laser and a 10^-16-fractional-frequency-stability superradiant active optical clock (AOC) have been achieved. However, never has a laser with atomic spontaneous radiation being destructively inhibited in an anti-resonant cavity where the atomic resonance is exactly between two adjacent cavity resonances been proven. Herein, we present the first demonstration of the inhibited stimulated emission, which is termed an inhibited laser. Compared with traditional superradiant AOCs exhibiting superiority for the high suppression of cavity noise in lasers, the effect of cavity pulling on the inhibited laser's frequency can be further suppressed by a factor of (2F/π)^2. This study of the inhibited laser will guide further development of superradiant AOCs with better stability, and may lead to new searches in the cavity quantum electrodynamics (QED) field.
We experimentally demonstrate the collective emission behavior and suppressed cavity-pulling effect of four-level active optical clock with Cesium atoms. Thermal Cesium atoms in a glass cell velocity selective pumped with a 455.5 nm laser operating at 6S1/2_{1/2}1/2​ to 7P3/2_{3/2}3/2​ transition are used as lasing medium. Population inverted Cesium atoms between 7S1/2_{1/2}1/2​ and 6P3/2_{3/2}3/2​ levels are optical weakly coupled by a pair cavity mirrors working at deep bad-cavity regime with a finesse of 4.3, and the ratio between cavity bandwidth and gain bandwidth is approximately 45. With increased 455.5 nm pumping laser intensity, the output power of cesium active optical clock at 1469.9 nm from 7S1/2_{1/2}1/2​ level to 6P3/2_{3/2}3/2​ level shows a threshold and reach a power of 13 μμμW. Active optical clock would dramatically improve the optical clock stability since the lasing frequency does not follow the cavity length variation exactly, but in a form of suppressed cavity pulling effect. In this letter the cavity pulling effect is measured using a Fabry-Perot interferometer (FPI) to be reduced by a factor of 38.2 and 41.4 as the detuning between the 1469.9 nm cavity length of the Cs active optical clock and the Cs 1469.9 nm transition is set to be 140.8 MHz and 281.6 MHz respectively. The mechanism demonstrated here is of great significance for new generation optical clocks and can be applied to improve the stability of best optical clocks by at least two orders of magnitude.
An ideal superradiant laser on an optical clock transition of noninteracting cold atoms is predicted to exhibit an extreme frequency stability and accuracy far below mHz-linewidth. In any concrete setup sufficiently many atoms have to be confined and pumped within a finite cavity mode volume. Using a magic wavelength lattice minimizes light shifts and allows for almost uniform coupling to the cavity mode. Nevertheless, the atoms are subject to dipole-dipole interaction and collective spontaneous decay which compromises the ultimate frequency stability. In the high density limit the Dicke superradiant linewidth enhancement will broaden the laser line and nearest neighbor couplings will induce shifts and fluctuations of the laser frequency. We estimate the magnitude and scaling of these effects by direct numerical simulations of few atom systems for different geometries and densities. For Strontium in a regularly filled magic wavelength configuration atomic interactions induce small laser frequency shifts only and collective spontaneous emission weakly broadens the laser. These interactions generally enhance the laser sensitivity to cavity length fluctuations but for optimally chosen operating conditions can lead to an improved synchronization of the atomic dipoles.
Abstract The concept of the active optical clock (AOC) was proposed seventeen years ago by prof. Jingbiao Chen. After early calculations and experiments that demonstrated the advantages of “cavity-pulling suppression” and “narrower linewidth”, the development of AOCs soon became an active competition involving many research groups that proposed schemes based on different atomic species, and different energy-level structures. In this paper, after a brief background introduction, we will mainly focus on the most recent experimental and theoretical progress of AOCs in Peking University. In addition, we give an outlook on AOCs based on cold atoms that can be operated continuously, and report a novel AOC scheme based on diffuse laser cooling that can be operated continuously for the first time, which is proposed and performed by Peking University. The AOC has great promise for applications in quantum metrology, as it can overcome the thermal noise of the reference cavity that limits conventional lasers, making AOC a promising candidate for future atomic optical clocks.
We have experimentally demonstrated the active optical clock with a good suppression to cavity-length noise compared with the passive one. However, the frequency stability of the four-level active optical clock for thermal atoms is still limited by the residual cavity-pulling effect. In this paper, we preliminarily realized the cavity-length stabilization in 1064/1470 nm dual-wavelength good-bad cavity system. The synchronous cavity-length change between two dual-wavelength systems is realized by using the phase locking technique of 1064 nm goodcavity lasers. Therefore, the beating linewidth of 1470 nm badcavity lasers will also be reduced considering that the 1064/1470 nm dual-wavelength lasers share the one cavity. The tracking accuracy of 1064 nm good-cavity lasers is better than 3×10-16at 1 s after phase-locking, and the linewidth of 1470 nm bad-cavity laser is reduced to 77 Hz. The linewidth of active optical frequency standard is still limited by the light shift, collision shift and Zeeman shift. The beating signal of magnetic sublevels corresponding to the Cs 1470 nm clock transition is observed under Zeeman effect. Further research is needed, such as, the design of vacuum chamber and magnetic shielding, to reduce the linewidth of the continuous 1470 nm active optical frequency standard.