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Working Group 4.31

Super-stable Laser Sources with Sub-Hertz Linewidth

In collaboration with several German and international groups we generate laser radiation with highest stability and lowest line width. To this end, we stabilize the frequency of the lasers to the eigenfrequencies of ultra-stable optical resonators made from special glass or single-crystalline materials.  

Cryogenic silicon resonator:

Optical atomic clocks are surpassing the best caesium atomic clocks with respect to frequency stability and accuracy. Today the frequency stability of the best optical atomic clocks is still limited by the frequency stability of the ultra-stable lasers that interrogate the reference transition in atoms or ions (the “pendulum” of the clock). In our project we aim to improve the stability of the laser systems and to utilize this stability in superior optical clocks  (in Working Group 4.32, Working Group 4.43 and QUEST@PTB)

 

 Silicon resonator with silicon mirrors

An ultra-stable laser system comprises of a laser whose frequency is stabilized to a narrow resonance line of an optical resonator. The resonator comprises of two mirrors with optimal reflectivity that are connected to a spacer. The laser radiation with the stabilized frequency can be transferred to laser sources in different wavelength regions by use of a femtosecond frequency comb virtually without degradation of the frequency stability. Any variation of the optical path length between the mirrors results in a variation of the frequency of the stabilized laser which is proportional to the length variation. Thus, the resonator must be isolated from variations due to temperature and vibrations. The best lasers of today are limited by thermal fluctuations of the resonator length i.e. by Brownian motion of the molecules in the resonator material.

 

 Set up of the cryostat for the silicon resonator

To reduce the frequency fluctuations, we decrease the temperature of the resonator near 124 K where the constant of thermal expansion of silicon is zero. We furthermore chose a material with high mechanical figure of merit. We use a resonator of 21 cm length made from a single silicon crystal.  With this resonator, we could demonstrate a relative frequency instability near 4 x 10-17 thereby realizing one of the most stable laser worldwide. These investigations are performed in close cooperation with the research group of   Prof. Jun Ye (JILA, USA).

Selected Publications:

D. G. Matei, T. Legero, S.  Häfner, C.  Grebing, R. Weyrich, W. Zhang, L. Sonderhouse, J. M. Robinson, J. Ye, F. Riehle and U. Sterr: „1.5 μm lasers with sub 10 mHz linewidth“
Phys. Rev. Lett., 118, 263202 (2017),  doi: 10.1103/PhysRevLett.118.263202 preprint: Opens external link in new windowarXiv:1702.04669v4 [physics.ins-det]

D. G. Matei, T. Legero, C. Grebing, S. Häfner, C. Lisdat, R. Weyrich, W. Zhang, L. Sonderhouse, J. M.  Robinson, F. Riehle, Ye, J. and U. Sterr:
“A second generation of low thermal noise cryogenic silicon resonators”
J. Phys.: Conf. Ser., 723, 012031 (2016) doi:10.1088/1742-6596/723/1/012031

S. Häfner, S. Falke, C. Grebing, S. Vogt, T. Legero, M. Merimaa, C. Lisdat and U. Sterr:
“8 × 10-17 fractional laser frequency instability with a long room-temperature cavity”
Opt. Lett., 40, 2112-2115 (2015), Opens external link in new window doi: 10.1364/OL.40.002112

C. Hagemann, C. Grebing, C. Lisdat, S. Falke, T. Legero, U. Sterr, F. Riehle, M. J. Martin, and J. Ye: "Ultra-stable laser with average fractional frequency drift rate below 5×10−19/s", Opt.Lett. 39, 5102-5105 (2014), doi: 10.1364/OL.39.005102 preprint: arXiv:1405.1759  [physics.optics]

W. Zhang, M.J. Martin, C. Benko, J.L. Hall, J. Ye, C. Hagemann, T. Legero, U. Sterr, F. Riehle, G.D. Cole and M. Aspelmeyer: "Reduction of residual amplitude modulation to 1 × 10⁻⁶ for frequency modulation and laser stabilization", Opt.Lett. 39, 1980-1983 (2014), doi: 10.1364/OL.39.005102

T. Kessler, C. Hagemann, C. Grebing, T. Legero, U. Sterr, F. Riehle, M. J. Martin, L. Chen, and J. Ye.: "A sub-40-mHz-linewidth laser based on a silicon single-crystal optical cavity", Nature Photonics 6, 687-692 (2012), doi: 10.1038/NPHOTON.2012.217

C. Hagemann, C. Grebing, T. Kessler, S. Falke, N. Lemke, C. Lisdat, H. Schnatz, F. Riehle, and U. Sterr: "Providing 10-16 short-term stability of a 1.5 µm laser to optical clocks", IEEE Trans. Instrum. Meas. 62, 1556-1562 (2013), doi: 10.1109/TIM.2013.2242597 

Contact

Dr. Uwe Sterr
Tel.: +49 (0)531-592 4310
E-Mail: Opens window for sending emailUwe Sterr

 

Dr. Thomas Legero
Tel.: +49 (0)531-592 4306
E-Mail: Opens window for sending emailThomas Legero