Exceptional Drift Stability: Cryogenic Wide-field Microscopy
When dealing with optical microscopy at low temperatures, one pre-requisite of paramount importance is the spatial stability: scarce optical signals such as those from single photon sources often imply long acquisition times, and hence require conditions as stable as possible over extended measurement periods. Temperature fluctuations and gradients, combined with mismatched thermal expansion coefficients among the parts, can jeopardize the acquisition of images over a range of temperatures or longer periods of time.
The LT-APO configuration of the attoDRY800 with cold apochromatic objectives has been expressly designed in order to optimize the stability performance. Overall, this minimizes thermal drifts significantly compared to optics sitting at room temperature - be it in vacuum or outside of the cryostat:
· no measurable drift over 40 h at base temperature, and up to 30 K
· smaller by almost a factor of 20 compared to warm objectives over the full temperature range
Also, vibrations are absolutely no concern since there is no measurable difference between cryocooler ON and OFF configuration even at ultimate resolution.
A nanoscale quantum sensor at high pressures
Pressure affects phenomena ranging from the properties of planetary interiors to transitions between quantum mechanical phases. However, the enormous stress gradients generated in high pressure experimental apparatuses, such as the diamond anvil cell, limit the utility of most conventional spectroscopy techniques. To address this challenge, a novel nanoscale sensing platform was independently developed by three groups (given in alphabetic order): the Jean-Francois Roch group (Université Paris-Sud, FR), the Sen Yang group (Chinese University of Hong Kong, CN), and the Norman Yao group (University of California, Berkeley, USA). The researchers used quantum spin defects integrated into an anvil cell to detect minuscule signals under extreme pressures and temperatures with diffraction-limited spatial resolution.
For this purpose, Norman Yao and colleagues utilized the table-integrated closed cycle attoDRY800 cryostat - the ideal platform for precise and rapid temperature control of a diamond anvil cell while offering a large sample chamber and free-beam optical access. The convenience of the closed-cycle cryostat allowed the researchers to publish their results to arXiv just nine months after installation.
S. Hsieh et al., Imaging stress and magnetism at high pressures using a nanoscale quantum sensor, arXiv:1812.08796 (2018)
M. Lesik, et al., Magnetic measurements on micron-size samples under high pressure using designed NV centers, arXiv:1812.09894 (2018)
K. Yau Yip et al., Quantum sensing of local magnetic field texture in strongly correlated electron systems under extreme conditions, arXiv:1812.10116 (2018)
Non-equilibrium phase transitions in quantum fluids of light
The understanding of many quantum phenomena in solid state physics heavily relies the ability to measure the dispersion relation of the fundamental excitations of the system. In the blossoming field of cavity polariton research, this dispersion relation is directly encoded in the propagation direction of the light emitted by the sample. To decrease the background signal and, therefore, increase the detected signal's quality, thin planar samples are used to perform transmission spectroscopy measurements. The group of Martin Kroner (ETH Zürich, Swizerland) performs such spectroscopy measurements using a table integrated closed cycle cryostat, the attoDRY800, as cold platform for the sample. By allowing for free space optical access to the sample from both sides, the attoDRY800 setup is an ideal platform to carry transmission measurements. In addition, the cold platform’s compactness results in a high stability and leaves most of the optic’s table space for the optical setup.
Link to the group's webpage
Polariton dispersion in strong coupling regime
The group of Prof. Atac Imamoglu (ETH Zurich) uses the attoDRY800 for phase contrast microscopy. The video (link below) shows the polariton dispersion in the so-called strong coupling regime, measured via white light transmission. The x-axis represents the in-plane momentum k||, the y-axis the energy E. The time evolution is given by the exciton-cavity detuning. In the inset, the corresponding spectrum at k|| = 0 is shown.
(Data courtesy of Martin Kroner; video created by Thomas Fink and Olivier Faist; Quantum Photonics Group, ETH Zurich)
Related video on Youtube
Single Photon Generation with Controlled Polarization from InGaN Quantum Dots
The research groups led by Prof. R. Taylor & Dr. R.A. Oliver in the UK have successfully generated single-photons with polarized light emission and predefined polarization axis at temperatures spanning from around 5 K to above 200 K using InGaN quantum dots. These quantum dots offer several advantages, such as high experimental repetition rates in the range of GHz, and for their growth as a planar structure, a single routine without complex geometrical engineering.
The emission spectra of these quantum dots were characterized using micro-photoluminescence techniques, while the samples were kept cool inside an optical cryostat equipped with attocube positioners. This table top cryostat, the attoDRY800, is able to reach temperatures ranges from below 5 K up to even above 300 K with very good thermal and vibrational stability.
The single-photons generated by these quantum dots are bright enough to allow their optical properties to be measured even above 200 K, a temperature considered to be the Peltier cooling barrier. Hence, this suggests in principle, that these quantum dots could be applied in integrated electronic circuits. And thanks to the achievable polarization control, these quantum dots are good candidates for on-chip polarization encoding in quantum cryptography.
To know more about the work done by Robert Taylor, Rachel Oliver and their research teams, please visit their websites here: https://users.physics.ox.ac.uk/~rtaylor/ and here http://www.gan.msm.cam.ac.uk/directory/oliver
(Data courtesy of R. Taylor, Oxford University)