physics

Harald Schwefel

Harald Schwefel is a physics topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Harald Schwefel rather than just read about it. In short: Harald Schwefel is a German-born physicist currently based in New Zealand. He is a professor in the Department of Physics at the University of Otago and a principal investigator in the Dodd-Walls Centre.

Key takeaways

Harald Schwefel belongs to physics; place it in that map before memorising details.
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Reference excerpt

Harald Schwefel is a German-born physicist currently based in New Zealand. He is a professor in the Department of Physics at the University of Otago and a principal investigator in the Dodd-Walls Centre. His research focuses on the interaction of light and matter in dielectric materials, and his speciality is whispering gallery mode resonators (WGMRs), small disks of dielectric which confine and store laser light to facilitate nonlinear interactions. He uses these to generate optical frequency combs and to coherently convert between microwave and optical photons.

Biography Born in Berlin, Schwefel spent his undergraduate years from 1994 till 1998 studying physics and maths at Brandenburg University of Technology (BTU) Cottbus in Germany. During this time he took an active part in student politics as a member and then chairman of the student council StuRa. He organised strikes and demonstrations in response to savings plans proposed by Science Minister Steffen Reiche in a draft of the Brandenburg Higher Education Act that granted unlimited rights to close and merge universities. Schwefel was motivated to maintain the small size of universities in East Germany which offered educational advantages. He encouraged students to be active, enjoy student life and study subjects they found fun. He also ran the Berlin marathon and climbed Mount Elbrus while at BTU. In 1998 Schwefel received a graduate student scholarship from Yale University and studied the topic of chaotic dielectric resonators at Yale University with adviser Douglas Stone. During this time he worked as a maths and science tutor at Davenport College. He graduated with a PhD in 2004 and took a postdoctoral position in the same department, spending seven years in total at the Yale Physics Department. In 2005 he visited ATR Wave Engineering Laboratories in Kyoto Japan as a postdoctoral researcher. In 2005 Schwefel joined the Max Planck Research Group at the University of Erlangen as a postdoctoral fellow and then established a research programme as a group leader at the Max Planck Institute for the Science of Light in Erlangen. Schwefel moved to New Zealand in September 2015 where he has reestablished his research programme as a senior lecturer in the Department of Physics at the University of Otago and a principal investigator in the Dodd-Walls Centre for Photonic and Quantum Technologies.

Research

Schwefel leads the Resonant Optics group at the University of Otago. His research focuses on resonantly enhanced interaction of light and matter in dielectric materials. This includes both theoretical and experimental work in the linear and nonlinear domains. He specialises in whispering gallery mode resonators (WGMRs), small disks of dielectric materials which are used to confine, store and therefore intensify light to facilitate nonlinear interactions. These devices are based on the whispering gallery wave phenomenon, where laser light bounces around the inner surface of a dielectric disc, confined by total internal reflection. Schwefel began research on WGMRs at the Max Planck Institute and has further developed fabrication techniques to achieve high quality factors, which means that large amounts of laser light can be confined and stored within the resonator with very little leakage. The resulting high electric field strengths enable efficient nonlinear interactions. Schwefel's group are exploring the use of WGMRs for generating optical frequency combs, coherently converting microwave and terahertz radiation into the optical domain as well as other fundamental investigations.

Optical frequency combs and telecommunication Schwefel and his team have used WGMRs made of second order nonlinear crystals, such as lithium niobate, to generate optical frequency combs of record efficiency. These devices show potential to significantly improve the efficiency of the internet by reducing the power required to encode data and the information-carrying capacity of optical fibres. The frequency combs are generated by sending low power microwave and optical signals into a WGMR; the crystal is electro-optically active, so its optical properties change under the influence of an electric field. The electric field of the microwaves influences the light waves and as a result a cascade of over a hundred new optical frequencies are generated from the original optical frequency. The device produces 160 coherent laser frequencies at low power. They have potential use in submarine optical networks and data centres where a single optical frequency comb could replace over a hundred lasers currently used to encode and send data on optical fibres. Because all the laser lines generated are from the same source, they have the same noise characteristics and stable phase relation. This would allow the transport of more light down a single optical fibre, increasing its information-carrying capacity. Unlike the more common microresonator optical frequency combs, which are based on the third-order nonlinear Kerr effect, these optical frequency combs rely on a second-order nonlinear effect, which has enabled improvements in efficiency. Schwefel and his team are collaborating with New Zealand-based optical technology company Coherent Solutions to develop applications and are also investigating the use of their frequency combs for high-precision spectroscopy. The WGMRs also show potential for reducing the line-width of fibre lasers. Schwefel and his team have found that placing a WGMR as a passive filtering element within the loop of a fibre laser reduces the line width to sub-kHz levels, which improves the stability of the system.

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Illustrations

Worked examples

Example 1 — a first encounter with Harald Schwefel

Start with the simplest possible case. Write down what Harald Schwefel claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In physics, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Harald Schwefel before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Harald Schwefel ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Harald Schwefel

In research: Harald Schwefel appears in physics research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Harald Schwefel in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Harald Schwefel is common in secondary-school and first-year university syllabi. It links to neighbouring topics 21st-century German physicists, 21st-century New Zealand physicists, Academic staff of the University of Otago, so understanding it makes those chapters shorter.
In everyday life: Look for Harald Schwefel outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Harald Schwefel in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Harald Schwefel means in your own words.
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Work through the three examples above with pen and paper.
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Frequently asked questions

What is Harald Schwefel in simple terms?

Why does Harald Schwefel matter?

Because it connects several physics ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Harald Schwefel?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Harald Schwefel.