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Logo Institut für Halbleitertechnik der TU Braunschweig
Cavity Optomechanics
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Cavity Optomechanics

Cavity-Optomechanik

We explore the coupling of coherent light (laser radiation) with the motion of mechanical objects. Usually, these investigations take place in optical resonators (cavities). In addition to macroscopic couplings such as radiation pressure, we also investigate micro- and nanoscopic effects, particularly the interaction of the optical near field with micro- and nanostructured surfaces (so-called metamirrors). The coupling of thermal noise (Brownian motion) to the coherent light field is the limiting factor for many high-precision applications such as gravitational wave detectors and optical atomic clocks. By studying the coupling mechanisms and developing specialized metamirrors, it is possible to reduce this noise by several orders of magnitude. 

Low-noise metamirrors
Rauscharme Metaspiegel

Thermal noise in optical components sets a fundamental limit for many laser applications. In particular, gravitational wave detection and ultra-stable lasers for optical atomic clocks, ion trap quantum computing, and telecommunications in space benefit from low-noise optics. We are investigating various noise mechanisms that perturb optical signals and developing novel optical components with lower noise than those currently in use. In particular, microstructured surfaces exhibit low noise:

  • Brownian thermal noise in functional optical surfaces
    Kroker, S., et al. DOI: 10.1103/PhysRevD.96.022002
  • Influence of polarization and material on Brownian thermal noise of binary grating reflectors
    Dickmann, J., et al. DOI: 10.1016/j.physleta.2017.07.006

Other components such as beamsplitters also exhibit non-negligible noise:

  • Thermal noise of beam splitters in laser gravitational wave detectors
    Dickmann, J., et al. DOI: 10.1103/PhysRevD.98.082002
  • Thermal noise computation of arbitrary masses in optical interferometers from first principles
    Dickmann, J. DOI: 10.1364/oe.438507

We are developing hybrid mirrors with high reflectivity and low noise and studying them experimentally in ourlaboratories.

  • Highly reflective low-noise etalon-based meta-mirror
    Dickmann, J., and Kroker, S. DOI: 10.1103/PhysRevD.98.082003
  • Experimental realization of a 12,000-finesse laser cavity based on a low-noise microstructured mirror
    Dickmann, J., et al. DOI: 10.1038/s42005-023-01131-1

Likewise, we are constantly searching for novel noise sources:

  • Thermal charge carrier driven noise in transmissive semiconductor optics
    Bruns, F., et al. DOI: 10.1103/PhysRevD.102.022006
  • Thermally induced refractive index fluctuations in transmissive optical components and their influence on thesensitivity of Einstein telescope
    Meyer, J., et al. DOI: 10.1088/1361-6382/ac6e21

Contact: Dr. Johannes Dickmann

Cavity ringdown spectroscopy
Cavity-Ringdown-Spektroskopie

Measuring very high reflectivities > 99.9% is challenging because there is very little difference between theinput power and the reflected power. We have a setup for measuring very high reflectivities with decreasingmeasurement error the higher the reflectivity of the mirrors: cavity ringdown spectroscopy.

Instead of measuring the reflectivity directly, an optical resonator (cavity) consisting of the mirror to bemeasured and a reference mirror is set up. With the help of a tunable laser, an optical resonance is found in the cavity. This creates a strong coherent light field between the two mirrors. The irradiation is switched off,and the photon lifetime in the cavity is measured. This is a measure of the reflectivity of the mirrors.

With the cavity ring down, we investigate the low-noise microstructured mirrors and hybrid concepts with low noise and high reflectivity:

  • Experimental realization of a 12,000-finesse laser cavity based on a low-noise microstructured mirror
    Dickmann, J., et al. DOI: 10.1038/s42005-023-01131-1

Contact: Dr. Johannes Dickmann

Cavity optomechanics for fundamental science

With the help of ultrastable laser cavities, laws of fundamental physics 
can be investigated. In particular, we investigate the interaction of laser
light with gravity (special and general relativity):

  • Impact of Earth's gravity on Gaussian beam propagation 
    in hemispherical cavities
    Ulbricht, S., et al. DOI: 10.1103/PhysRevD.104.062002
  • Gravitational light deflection in Earth-based laser cavity experiments
    Ulbricht, S., et al. DOI: 10.1103/PhysRevD.101.121501

Contact: Dr. Johannes Dickmann

 

Cavity-Optomechanik für die Grundlagenforschung
Mechanical Quality Factor investigation
Untersuchung des mechanischen Q-Faktors

One of the most important quantities for low-noise optics is the mechanical quality factor (or mechanical loss). More precisely, the Brownian noise of optical surfaces is proportional to the mechanical loss. We investigate the mechanical quality of different material systems as a function of temperature (also cryogenic), geometry, and measurement frequency:

  • Mode-dependent mechanical losses in disc resonators
    Cagnoli, G., et al. DOI: 10.1016/j.physleta.2017.05.065
  • Fabrication of SiO2 microcantilever arrays for mechanicalloss measurements
    Mariana, S., et al. DOI: 10.1088/2053-1591/aafab7

Contact: Dr. Johannes Dickmann, Nico Wagner

Optomechanical light control
Optomechanische Lichtsteuerung

We study microstructured surfaces that exhibit strongly exaggerated optomechanical coupling. In particular, bound-states in the continuum are suitable for many applications: All-optical light control, saturable output couplers, and optomechanical generation of non-classical light:

  • Bound states in the continuum foroptomechanical 
    light control with dielectric metasurfaces
    Rojas Hurtado, C. B., et al. DOI: 10.1364/oe.392782

Contact: Dr. Johannes Dickmann

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