A marriage made in CLEO: astronomy/physics and photonics

My love for the stars is not new to some of you. So the tone of this post should not be a surprise.

At CLEO amongst other talks and sessions was a special symposium on

Advances and opportunities in Astro Photonics, JF1N. There were two particular talks that really caught my attention:

The first invited talk (JF1N.1) was by Olivier Guyon titled, “Where are our closest neighbours? Looking for life in nearby exo-planets”.

Exo-planets! Do you need to say even one word more to catch the interest of the people? For sure I was hooked by the title alone and the talk delivered. Some interesting facts that was thrown up in the talk included that about 10% of stars have potentially habitable planets around them. By habitable we mean a mass similar to the Earth and distance that is similar to the Earth from the sun, placing these planets in the habitable zone because that temperature would allow life and may enable liquid water to exist on the planet surface as well.

As the speaker pointed out the question is not if there is life out there but how close it is to us so we know where to look so we know where to look.

He then went on to talk about diff to talk different planet detection techniques: those that are indirect such as astrometry and radial velocity based and those that are direct.

The trouble with direct detection via telescopes on Earth is that the planets are so close to the star (angular separation over this huge distance is very small) that the light from the star far outshines the light reflected by the planet making it virtually invisible. This means we need other more clever ways of finding planets which obviously do not emit their own light.

Radial velocity has thus far been the most successful indirect technique in detecting exoplanets. It relies on the fact that a star also feels the gravitational tug of the planet/s orbiting it and executes motion along an orbit. The change (blue/red) shift of its spectral lines due to the Doppler effect in this orbital motion can be used to detect the presence of the exoplanet.

This technique would detect large planets close to the star in a short orbit, causing a wobble that is detectable. But such large planets close to the star are unlikey to host life. So other techniques are needed to detect smaller planets in the habitable zone.

Astrometry the second technique discussed is where photonics will come in! The technique  relies on the motion of the star changing (a slight wobble if we plot the  projection of its motion around its centre of mass) and detecting this wobble. This would be of the order of a few micro arc seconds while ground based telescopes have detection capability of say half an arcsecond. Theoretically increasing the diameter of a telescope would make it capable of measuring smaller wobbles, but atmospheric turbulence decreases this. Use of adaptive optics is one way to combat it! As well as use of interference with astrometry in the VLTI.

I will blog about the second talk another day. Meanwhile happy reading on astrometry and astrophotonics!!

By artiagrawal Posted in General

Black Phosphorous and other things at CLEO 16

So I am back at CLEO for the third time teaching my short course on Finite Element Method again.

I had a busy 3.5 hours with the course, interacting with about 20 attendees who came to the course. It was much fun and afterwards I had two very interesting conversations on applying numerical methods:

  • what is the best method to use (BPM or FDTD) to study propagation and scattering in media with subwavelength disorder?
  • in highly dispersive materials close to epsillon being 0 (so resonances are present) how does one study non-linear effects in periodic structures where feature shape and size are important?

These sort of discussions are so exciting because they open my mind to new areas and challenge me to think about applying my knowledge and expertise in ways.

But that was not all. 

In talks I attended an invited talk on Optical Properties of Black Phosphorous (BP) stood out for me. This was in Session SW1R, the first talk by Xiamou Wang of Yale University. The authors gave some intriguing glimpses into what was a new topic for me. Graphene by now is well known as a 2D material. BP was a new material to me. It seems that it lies somewhere between Graphene and other Two Dimensional Materials (TDMs) such as Molybdenum DiSulphide. BP bridges the optical and electronic gaps.

The optical gap of Graphene is 0, while that of TDMs is large, BP is about 1.3eV for monolayer BP . The electronic gap bridge comes about because Graphene has low on/off ratio  and high electronic mobility, while TDMs have high on/off ratio and low mobility. BP has a medium on/off ratio and medium mobility.

Certainly of the 70 odd 2D materials available BP seems to be the new exciting thing! So it gives me something new to learn!

Some papers mentioned in the talk that you may want to look at:

PNAS, 112, 4253, 2015

Nano Letters, 14, 6414, 2014

Nature Photonics, 9, 247, 2015

Then there was the special symposium to mark 20 years of Photonic Crystal Fibers. In the symposium I really enjoyed the talk by Arnaud Mussot (SW1I.3) on topographic fibers. The central idea here is that the outer diameter (and through that the modal properties such as dispersion, non-linearity etc.) of the fiber can be varied along the length of the fiber. This variation can be sinusoidal or in some cases follow other profiles too. The applications discussed were on modulation instability, solitons. Though ofcourse there are many others. Some papers mentioned in the talk that you may want to look at:

Optics Letters, 37, 4832, 2012;

Physical Review A, 87, 013813, 2013;

Optics Express 23, 3869, 2015;

Optics Letters 40, 455, 2015;

Physical Review Letters, 116, 143901, 2016.

But that wasn’t all!

The event on Climbing the Ladder brought together 4 panellists who spoke of their career journeys. This was followed by lunch in which people sat in “mentor” or “mentee” chairs and talked to establish a mentor-mentee relationship.

So many of us feel we need some career advice (how to get a post-doc, how to change jobs, where to move to etc.) but we dont know whom to ask or how to find a good mentor. this was an opportunity to meet some excellent mentors and ask these questions, and perhaps start a longer relationship.

For mentors this was an opportunity to give back to the  community by supporting the next generation of professionals and leaders. Helping them navigate the choppy waters of education, careers and the intersection with personal life.

All in all it has been a superbusy and extremely rewarding time at CLEO, meeting people and networking, learning new things.

I hope I will see you there too in the future!