Two new methods for multiplexing a single laser cavity to support a pair of low noise optical frequency combs

We have invented two new methods for multiplexing a single laser cavity to support a pair of noise-correlated, yet cavity length independent optical frequency combs.

10.11.2022 by Ursula Keller

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The two methods are based on either polarization multiplexing with an intracavity birefringent crystal [1] or spatial laser cavity multiplexing by inserting a monolithic device with two separate angles on the surface, such as a biprism [2]. Single-cavity dual-comb applications represent a paradigm shift because no active stabilization is required. It was first demonstrated with dual-comb spectroscopy [3], but also applies to any pump-probe measurements.

The two cavity modes share all intracavity components and take a near-common path, but do not overlap on any active elements. With a SESAM we passively modelocked both independent modes and obtain dual-comb operation. We demonstrated this with both diode-pumped Yb-doped solid-state lasers and semiconductor lasers using the MIXSEL technology. The high-Q cavity allows for record-low noise performance.

Most recently [2] we have demonstrated a 80-MHz diode-pumped Yb:CaF₂ laser delivering more than 2.4 Watts of average power per comb with sub-140 fs pulses centered at 1052 nm. We reach sub-cycle relative timing jitter of 2.2 fs [20 Hz, 100 kHz] which is a major milestone in single-cavity dual-comb laser development which is also covered as an ETH, physics department news item.

With the spatial biprism multiplexing technique, we could implement slow feedback on the repetition rate difference Δf_rep, enabling this quantity to be drift-free, low-jitter, and adjustable over a large range – a key combination for practical applications that was lacking in many other single-cavity dual-comb systems. We could obtain record-level short- and long-term stability of σ(Δf_rep)/Δf_rep = 1.8 · 10^-7 in [20 Hz, 100 kHz] and 2.3 · 10^-7 σ(Δf_rep)/Δf_rep long-term stability over more than 5 hours (measured with a frequency counter). This translates to sub-cycle relative timing jitter and thus is a major step forward in the development of single-cavity dual-comb lasers.

Such lasers will have a great potential to revolutionize how any normal pump-probe measurements and optical spectroscopy are implemented.

[1] S. M. Link, A. Klenner, M. Mangold, C. A. Zaugg, M. Golling, B. W. Tilma, U. Keller
Download"Dual-comb modelocked laser" (PDF, 1.4 MB)
Optics Express, vol. 23, No. 5, pp. 5521-5531, 2015

[2] J. Pupeikis, B. Willenberg, S. L. Camenzind, A. Benayad, P. Camy, C. R. Phillips, U. Keller
Download"Spatially multiplexed single-cavity dual-comb laser" (PDF, 3.4 MB)
Optica, vol. 9, No. 7, pp. 713-716, 2022

[3] S. M. Link, D. J. H. C. Maas, D. Waldburger, U. Keller
Download"Dual-comb spectroscopy of water-vapor with a free-running semiconductor disk laser" (PDF, 583 KB)
Science, vol. 356, pp. 1164-1168, 2017