High-stability offset-frequency locking of two lasers using a balanced filter discriminator
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| Main Authors: | , , , , , , , , |
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| Format: | Preprint |
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2026
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| _version_ | 1866911697018552320 |
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| author | Park, Sang Eon Seo, Meung Ho Park, Young-Ho Hong, Hyun-Gue Lee, Sang-Bum Seo, Sangwon Lee, Jae Hoon Kang, Seji Kwon, Taeg Yong |
| author_facet | Park, Sang Eon Seo, Meung Ho Park, Young-Ho Hong, Hyun-Gue Lee, Sang-Bum Seo, Sangwon Lee, Jae Hoon Kang, Seji Kwon, Taeg Yong |
| contents | We demonstrate a high-stability laser offset-frequency locking technique based on a balanced filter discriminator. The beat note between two 852 nm external-cavity diode lasers is down-converted in two parallel arms using local-oscillator frequencies placed symmetrically around the desired offset frequency. After low-pass filtering and RMS detection, differential subtraction of the two detector outputs produces a dispersive frequency-error signal with a zero crossing primarily defined by the reference local-oscillator frequencies. This balanced configuration reduces sensitivity to common beat-power fluctuations and can improve the effective error-signal signal-to-noise ratio. The system was implemented for an 8.653 GHz offset corresponding to the cesium repumping frequency difference used in our laser-cooling setup. Measurements with different low-pass filters reveal a trade-off between discrimination sensitivity and feedback bandwidth. With an SLP-1.9+ filter, the locked beat frequency reached a fractional instability of $4\times10^{-15}$ at 10 s when referred to the 852 nm optical carrier. The residual dependence on photodetector optical power was also characterized, showing that amplitude-to-frequency conversion remains small in the optimized differential configuration. This approach provides a practical frequency-only offset-locking method for atomic-physics experiments requiring stable and tunable microwave-scale laser frequency offsets. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2605_19345 |
| institution | arXiv |
| publishDate | 2026 |
| record_format | arxiv |
| spellingShingle | High-stability offset-frequency locking of two lasers using a balanced filter discriminator Park, Sang Eon Seo, Meung Ho Park, Young-Ho Hong, Hyun-Gue Lee, Sang-Bum Seo, Sangwon Lee, Jae Hoon Kang, Seji Kwon, Taeg Yong Atomic Physics Applied Physics Optics We demonstrate a high-stability laser offset-frequency locking technique based on a balanced filter discriminator. The beat note between two 852 nm external-cavity diode lasers is down-converted in two parallel arms using local-oscillator frequencies placed symmetrically around the desired offset frequency. After low-pass filtering and RMS detection, differential subtraction of the two detector outputs produces a dispersive frequency-error signal with a zero crossing primarily defined by the reference local-oscillator frequencies. This balanced configuration reduces sensitivity to common beat-power fluctuations and can improve the effective error-signal signal-to-noise ratio. The system was implemented for an 8.653 GHz offset corresponding to the cesium repumping frequency difference used in our laser-cooling setup. Measurements with different low-pass filters reveal a trade-off between discrimination sensitivity and feedback bandwidth. With an SLP-1.9+ filter, the locked beat frequency reached a fractional instability of $4\times10^{-15}$ at 10 s when referred to the 852 nm optical carrier. The residual dependence on photodetector optical power was also characterized, showing that amplitude-to-frequency conversion remains small in the optimized differential configuration. This approach provides a practical frequency-only offset-locking method for atomic-physics experiments requiring stable and tunable microwave-scale laser frequency offsets. |
| title | High-stability offset-frequency locking of two lasers using a balanced filter discriminator |
| topic | Atomic Physics Applied Physics Optics |
| url | https://arxiv.org/abs/2605.19345 |