Crystalline supermirrors to advance sensing and detecting

Share this on social media:

Low-loss mirrors are a key technology for many different research fields. (Image: Yury Zap/Shutterstock.com)

A low-loss mid-infrared mirror using a crystalline coating technology has been developed

Physicists have developed high-performance laser mirrors in the sensing-relevant mid-infrared wavelength range that absorb less than ten out of a million photons. Manufactured in a new process based on crystalline materials, these low-loss mirrors promise to open up completely new application areas, for example in optical respiratory gas analysis for early cancer detection or the detection of greenhouse gases.

The work, published in May in Optica, involved a team made up of scientists from the University of Vienna, together with Thorlabs, the National Institute of Standards and Technology (NIST), and the University of Kansas.

In 2016 researchers at the Ligo laser interferometer succeeded in the first direct observation of gravitational waves, which had originally been predicted by Albert Einstein in 1916. A significant contribution to the observation of this wave-like propagation of disturbances in space-time, which was rewarded with the Nobel Prize a year later, was provided by the laser mirrors of the kilometre-long interferometer assembly.

Optimisation of these mirrors for extremely low optical absorption losses was a key advance in realising the sensitivity necessary to make such measurements. ‘Low-loss mirrors are a key technology for many different research fields,’ explained Oliver Heckl, head of the Christian Doppler Laboratory for Mid-IR Spectroscopy and Semiconductor Optics, ‘They are the link for such diverse research fields as cancer diagnosis and gravitational wave detection.’

In fact, comparable mirror properties are also promising technological breakthroughs for significantly more practical applications. This includes, among other things, sensitive molecular spectroscopy, i.e. the detection of the smallest amounts of substances in gas mixtures – a research focus of the Christian Doppler Laboratory (CDL). Examples can be found in the early detection of cancer through the detection of the smallest concentrations of marker molecules in the breath of patients, or in the precise detection of methane leaks in large-scale natural gas production systems in order to limit the contribution of such greenhouse gases to climate change.

Unlike the experiments at Ligo, however, such investigations are conducted much further outside the visible light spectrum, in the mid-infrared range. In this wavelength region, many structurally similar molecules are clearly distinguishable on the basis of their characteristic absorption lines. Therefore, it is a longstanding wish of the photonics community to realise similarly low loss levels in this technically challenging wavelength range.

This is exactly what the team led by Oliver Heckl has now achieved in international cooperation. In this case, low loss means that the new type of mirror absorbs less than 10 out of a million photons. This dramatic improvement was made possible through the use of a completely new optical coating technology: First, single crystal stacks of high-purity semiconductor materials are deposited via an epitaxial growth process. These monocrystalline multilayers are then transferred via a proprietary bonding process onto curved silicon optical substrates, completing the mirrors that were tested at both the CDL and NIST. This ‘crystalline coating’ technology was developed and carried out by the industrial partner of the Christian Doppler Laboratory, Thorlabs Crystalline Solutions. This company was originally founded under the name Crystalline Mirror Solutions (CMS) in 2013 as a spin-off from the University of Vienna by Garrett Cole and Markus Aspelmeyer. CMS was acquired by Thorlabs in December 2019. This industry collaboration was made possible with the support of the Federal Ministry for Digital and Economic Affairs, via the internationally unique model of the Christian Doppler Research Association (CDG) to promote application-oriented basic research.

‘Precise measurement technology is much more than just pedantry. Wherever you can take a closer look by an order of magnitude, you usually discover completely new phenomena, just think of the invention of the microscope and telescope!,’ said Georg Winkler, co-author of the current study.

In fact, this assessment has already proven true in the detailed characterisation of the new mirrors themselves, when a previously unknown effect of polarisation-dependent absorption was discovered in the semiconductor layers and theoretically explored by collaborator Prof. Hartwin Peelaers at the University of Kansas. ‘These results open up great opportunities regarding further refinement of these mirrors,’ co-author Lukas Perner said. ‘Thanks to the extremely low losses can we now further optimise the bandwidth and reflectivity.’

With this in mind, the project partners are already working on a further improvement of the technology: Expansion of the optical bandwidth of the mirrors will allow them to be used efficiently with so-called optical frequency combs. This will enable the analysis of particularly complex gas mixtures with unprecedented accuracy.

--

 

Featured Product: Stemmed Mirrors from Edmund Optics

Stemmed Mirrors are one of the latest product innovations from Edmund Optics, a global leading producer of optical and imaging components. The Stemmed Mirrors’ patent-pending design can achieve a higher surface flatness than conventional λ/10 flat mirrors when mounted into kinematic mounts.

Positioning and securing conventional flat mirrors in a kinematic mount applies pressure to their edges, imparting stress and degrading the mirror’s surface flatness. This can mean that in reality, a mirror of flatness λ/10 can actually become λ/5!

Instead, Edmund Optics’ Stemmed Mirrors are designed to be mounted by a stem on their back surface, reducing the stress imparted on the optical surface of the mirror and retaining its surface flatness.

Stemmed Mirrors are a cost-effective replacement for a more expensive and complex kinematic mount and conventional mirror setup. They are available in standard metallic coatings as well as dielectric coatings for applications requiring higher performance.

Further information www.edmundoptics.eu/f/stemmed-mirrors/39665

--

Featured Product: Optical Lenses from CeNing Optics

CeNing Optics, found in 2004, is offering high quality optical lenses including singlet lenses, doublet lenses, cylindrical lenses and powell lenses. The lens' materials are from Schott, CDGM, Ohara glasses.

The lenses come with diameters available from 1mm to 250mm. The best surface quality we can reach are 10-5 S/D and 0.2 irregularity and 30 arcsec centration. Addtional antireflective coating and high reflective coating can be applied on the surfaces upon request.

All leneses are available in custom design and standard design. CeNing offers lenses from prototype to volume production with a reasonable cost.

For more information, please visit our website: www.cn-optics.com/products/Lenses.asp

--

Featured Product: Spherical lenses from Manx Precision Optics

Manx Precision Optics is a family-owned manufacturer of high-quality laser optical components.

As part of our extensive product portfolio, we offer large spherical lenses (diameters over 100mm/4”) which complement our range of large flat optics for ultrafast and highpower laser applications.

All lenses are ground and polished, with a high laser-induced damage threshold (LIDT) in mind and coating (if required) can be applied in-house. This process allows us to guarantee the overall performance of all lenses in terms of LIDT. Typical LIDTs offered are >10J/cm2 in 1ns at 1,030nm.

Having an ISO 9001:2015 certified manufacturing process ensures we have total control over the final product. We also work alongside our customers, ensuring we find the best solution for them in terms of performance, cost and metrology requirements.

Please do not hesitate to contact us (sales@mpo.im) if you would like to find out more or discuss your requirements for optical components in more detail. https://mpo.im/products

--

Featured Product: High Precision Monolithic Retroreflectors from Spectrum Scientific, Inc.

Spectrum Scientific’s hollow retroreflectors have a rugged, one-piece construction and are manufactured from solid aluminum making them insensitive to vibration, position and movement. Custom mounting features can be directly machined and incorporated into the retroreflectors for easy alignment giving additional design and cost benefits. These mirrors are ideal for use in Michelson type interferometers, FTIR spectrometers and laserbased tracking systems.

Key advantages of our hollow retroreflectors include:

  • Ability to incorporate mounting features and fiducials onto the retroreflector itself
  • Reduces alignment considerations
  • Return beam accuracy < 2 arcsec
  • Gold or Aluminum coating (bare metal or with protective overcoat)

For volume pricing or custom designs, please complete our Request Information form or contact our sales team to discuss your specific requirements.

Further information www.ssioptics.com/product-category/precision-mirrors/hollow-retroreflectors