What do I actually do? Part 2: Lasers

In a previous post I introduced some of the basics of what I do as part of my DPhil (the Oxford term for a PhD: actually more English as the term PhD, I believe, originates in America.)  In this post I will cover a bit more about the lasers we use to perform these experiments.

I mentioned two concepts in the last post: Lasers and Plasmas.  We use lasers to create a plasma in the lab, but what exactly is a laser and why can it be used to make plasmas?

LASERs – “A solution looking for a problem”*

When they were first discovered no one could think of a use for them.  However lasers are now ubiquitous in our lives: from DVD or Blu-Ray players to barcode readers, medical applications (eye surgery, skin treatments) to science research, lasers have made a big impact.

Laser is actually an acronym which stands for Light Amplification by Stimulated Emission of Radiation.  Effectively a laser is a very special source of light that has specific properties:

  • It is coherent – this allows the light to be focussed very tightly,
  • Many can be made with only a single colour of light (wavelength),
  • It is highly directional – unlike a normal light, you tend not to be able to see a laser if you are side on to the direction the light is moving,
  • It can be amplified to contain a large amount of energy, in a short amount of time.

The light in a laser comes from atoms within the material.  Atoms are made up of a positive nucleus around which negative electrons move.  The electrons are arranged into certain positions (which we call orbits) around the nucleus, and they want to be as close to the nucleus as possible.

We can see the nucleus with the electron orbiting.  The orbitals are shown in different colours increasing in distance from the nucleus.  To the side we see these orbitals arranged in terms of energy.  The electron is sitting in the lowest energy level.

We can see the nucleus with the electron orbiting. The orbitals are shown in different colours increasing in distance from the nucleus. To the side we see these orbitals arranged in terms of energy. The electron is sitting in the lowest energy level.

An electron can absorb light and move further from the nucleus, gaining in energy.  Now the electron is in a higher energy level than it wants to be, so it can emit light and drop back down, we call this Spontaneous Emission.  In certain cases, the electron can be made to emit energy if light comes along that has the same amount of energy as the electron wants to lose.  In this case twice the amount of light comes out – the original light and the light from the electron – with the same energy and both are coherent.  This is called Stimulated Emission and is the basis for a laser working!  We call these individual pieces of light ‘photons’.

In Absorption, a photon of light comes in and is absorbed by the electron. The electron moves further from the nucleus, increasing in energy. In Spontaneous Emission, an excited electron decides it doesn't want so much energy, so releases a photon and drops back down to a lower energy orbit. In Stimulated Emission, a photon with energy equal to the separation of the two energy orbits stimulates the electron to emit a photon and drop down.

In Absorption, a photon of light comes in and is absorbed by the electron. The electron moves further from the nucleus, increasing in energy. In Spontaneous Emission, an excited electron decides it doesn’t want so much energy, so releases a photon and drops back down to a lower energy orbit. In Stimulated Emission, a photon with energy equal to the separation of the two energy orbits stimulates the electron to emit a photon and drop down.

*This appears to be what was said about lasers when they were first discovered, however I can’t find the original quote, or who even said it!

The Physical “Machine”

Now that we know how light and matter can interact, we can put together an actual laser.

We need:

  1. A source of photons,
  2. A way of making sure that once one photon of light is released, it goes on to stimulate more photons being released.

This, is turns out, is solved using special crystals and mirrors.

We place a crystal between two mirrors: we call this a cavity.  Around the crystal we place lamps, know as flash lamps.  These are just like standard bulbs, and they are designed to repeatedly flash on and off around the crystal.  As they emit light, the electrons in the crystal absorb this and raise their energy level.  Some electrons will then decide to drop down and release a photon of energy (the squiggly lines in the photo below.)  This light is released in random directions, however if one happens to travel along the direction that it hits one of the mirrors and is reflected back into the crystal, this can stimulate another electron to drop down, and now we get 2 photons: doubling the light!  These then reflect off the other mirror and return to the crystal where these two photons stimulate two electrons to emit and now we get 4 photons.  This carries on until we have a vary high number of photons!

Showing a schematic of a laser.

Showing a schematic of a laser.  The squiggly red arrows are spontaneously emitted photons, the heavy red arrows are photons that have been emitted by stimulated emission.

One of the mirrors is not completely reflective, so it allows some light through.  As the amount of light in the cavity increases, so too does the output.  This output is the laser light!

A laser can be used to create a plasma

As I mentioned in my previous post, and earlier, we use lasers to create plasmas that we are interested in studying.  But how does this work?

An experiment showing the light emitted from a plasma that was formed when the laser was fired onto a carbon rod (much like a pencil lead).

An experiment showing the light emitted from a plasma that was formed when the laser was fired onto a carbon rod (much like a pencil lead).

A plasma is formed by separating electrons from their atoms.  This takes a lot of energy, and laser light contains a lot of energy.  When the laser hits onto a piece of material, the light is absorbed by the electrons in the atom.  However; whereas before when the flash lamp caused an electron to increase in energy but stay in an orbital of the atom, here the energy is high enough that the electron can be kicked out of the atom completely.  When an electron leaves its parent atom, this is known as ionisation.  As the laser is so intense (there is a lot of light in a short amount of time and area), many electrons absorb the energy, so many atoms can be ionised multiple times.

These electrons are now have a lot of energy, and are hot: they move around very fast.  Whereas the atoms before were neutral and happy, now the electrons (negatively charged) are moving separately from the remaining ions (positively charged).  As there is a separation of the charge, electric forces can act between the two.  In this way the ions can also gain energy from the electrons.  (This is a simplified view of how energy is given to the electrons and ions as there can be many other processes.  However it is sufficient to get a general idea of what is happening.)  Voilà: a plasma is formed!

What Next?

We now know how lasers work, and that we can produce plasmas with them.  But, how can we use lasers to recreate a star in a lab?  Tune in next time to find out!

Physics on Both Sides of the Pond

February saw my return to San Francisco (more specifically Livermore) for the NIF/JLF User Group meeting.  NIF stands for “National Ignition Facility” and is, currently, the most energetic laser system on Earth.  (The word choice of ‘energetic’ may seem odd here, but there is a good reason for this which I will cover in one of my future posts on Physics.)  JLF is the “Jupiter Laser Facility”, which is a smaller laser system, which is more ‘hands on’.

The purpose of this meeting is to discuss science that is happening at these facilities, of which there was significant interest in recent experiments at NIF.  Previously NIF was almost exclusively used for the National Ignition Campaign [NIC], which is a series of experiments aiming to create viable fusion energy power using lasers.  (This will also be a topic in a future Physics post.)  However, recently, some time has been given to experiments and so new, and interesting, data were shown.

There was also a poster competition for students, and I am happy to say that I won 2nd Prize!  Visiting Alcatraz, the warm weather and catching up with many colleagues also made this trip quite enjoyable.

The inside of one of our lasers.  All those mirrors need to be precisely aligned, whilst also wearing goggles to block the hazardous emission (like that mass of green).

The inside of one of our lasers. All those mirrors need to be precisely aligned, whilst also wearing goggles to block the hazardous emission (like that mass of green you can see on the left).

Back in Oxford I shifted scale somewhat and have been more involved with getting our laser to work in the lab.  Lasers can be temperamental things, and if they are not maintained (or even used!) frequently, then it can take a while to coax them back to being useful.  Thus much of the time in our lab has been spent ‘coaxing’, but it is slowly coming together.

We also recently had a productive meeting relating to the experiment that we carried out last year.  We are now approaching the point of polishing a paper on the results.  I have high hopes!

What do I actually do? Part 1: Space and the Lab

I thought I would kick-start the year with a little Physics 101 on what I actually do.  Most people would probably know that I do Physics, and some may be able to say Laser Physics if pushed, but what does this actually mean and what is the point?


Laboratory Astrophysics

First things first: the area of my research.  The above phrase is not, surprisingly, an oxymoron.  My work can be described as trying to replicate the conditions of space, but within the laboratory.  There are many questions that can follow from this, so I will try and answer briefly below!


Why?

When we look at space, and see the amazing photos from the Hubble Space telescope, it is easy to see why astrophysics is so popular.

However sometimes we forget just how massive these features are, and how far away they are.  For example, the Crab Nebula, which is home to a supernova remnant (the aftermath of a violent death of a star), is over 6,500 light years away, and 11 light years wide.  (A light year corresponds to the distance light can travel in a year.  As light travels very fast, this distance is huge: 1 light year is the same as 9,461,000,000,000 km (or 5.9 trillion miles)!)

Because of these huge distances, what we are seeing is what happened to that phenomenon many years ago in the past and because they are so huge, they evolve very slowly in time.  If we want to understand what is happening, we have to hope that we are pointing the telescope in the right direction and wait!  This was how astronomy was, and still is, done.  Many images are taken over many years, and we try to piece together what is happening from this data.  However you can imagine that we are restricted in what we can see, as we can only look passively, not actively probe the system.

The Crab Nebula as seen by NASA's Hubble Space Telescope.

The Crab Nebula as seen by NASA’s Hubble Space Telescope.

Laboratory Astrophysics tries to overcome this problem by recreating these systems in the lab.  If we can recreate a star explosion in the lab, then we can probe it with lasers and other diagnostics to much better understand what is going on.  If we do this then we improve our knowledge of the Universe by relating these lab experiments to the stars.


How?

I stressed that the scales in astrophysics are massive: how can anything done in the lab (which is the size of cm and m) ever help us to understand space?

The majority of the material in the universe is in a state of matter called Plasma.  In school we learn about solids, liquids and gases.  The difference between these states is in the ordering of the atoms or molecules that make up the material.  Plasma can be thought of like a gas, but one that has been ionised.

(Atoms are made up of a positive centre (the nucleus), and negative orbiting charge (electrons).  In neutral material the charge from the positive centre matches the negative charge around it, but when we ionise a material then the negative charge disassociates from the positive centre and so we now have positive and negative parts that are separated in the material.)

Plasma acts in a similar way to a gas, but because of the positive and negative charges, it can be affected by magnetic and electric fields.

Positive nucleii, in red, are separated from the negative charges, in blue, in a plasma.  This gives the plasma special properties compared to a gas!

Positive nucleii, in red, are separated from the negative charges, in blue, in a plasma. This gives the plasma special properties compared to a gas!

Liquids, gases and plasmas can be described as fluids.  It may seem odd to describe a gas as a fluid, but if we think about the atmosphere of the earth, the gas acts in a very similar way to a liquid in a glass!  We can use a set of equations to describe how the fluid will act, and this type of physics is called fluid, or hydro, dynamics.  As plasmas have charges and are affected by electric and magnetic fields, we can adapt these equations to give magnetohydrodynamics [MHD] which we can then use to describe how a plasma acts.

Stars, supernovae and the inter-stellar medium of space are all plasmas.  We can also create plasmas within the laboratory.

A very handy property of these MHD equations is that they can be written in a form that does not depend on the scale.  What this means physically is that we can do experiments in the lab, and then relate this to what happens in space!  This gives us a much better chance to work out what is happening: we can create astrophysical phenomena on demand, and then actively probe them in the lab.

What?

This sounds excellent, but how do we actually make plasmas in the lab, and how can we make sure these are similar to stars?  Find all this out in part 2 coming soon!

HPL Christmas Meeting 2014

Directly after Iceland I headed to the High Powered Laser Christmas Meeting: a relaxed conference of, mostly, student posters and presentations that, informally, marks the end of the year.

I was quite happy to be named the winner of the poster competition during the Christmas dinner, and celebrated appropriately in Abingdon afterwards.  There was, of course, the obligatory Christmas Jumper photo.

It has to be done really!

It has to be done really!

Merry Christmas everyone!

Paris Experiment and Iceland

After New Orleans I had a brief time back in Oxford – where I tried, unsuccessfully, to help get an experiment working in the lab – before I headed out to Paris for an experiment which followed on from those at Orion.

The target mount for our experiment.  It really is that small!

The target mount for our experiment. It really is that small!

The experiment had a few teething issues related to the laser (hey, it’s a laser facility, if everything ran smoothly something would be wrong!) but I think some interesting data were generated that should keep everyone busy for a while!

I stayed in Paris so I commuted into Ecole Polytechnique in Palaiseau every day.  This went surprisingly smoothly for the majority of the time (the RER B is well known for it’s, ahem, irregularity) but I did notice a few differences in “railway culture” from the UK:

  • On the underground, people try and get on at the same time as people getting off.  This was very confusing as it resulted in the whole thing taking longer as people tried to push through in both directions.  It may be a stereotype of the English, but it seems queuing works!
  • When people boarded the metro, they seemed to just stop, even if this was in the way of the door.
  • On the RER (a type of train half-way between the overground and underground in London) people seemed to favour sitting in the direction of travel over having not to share seats next to each other.  In England it seems so abhorrent to sit next to each other when seats are available that allow a gap from your fellow passengers, but in France they choose the more pleasant facing direction of travel over this.

Whilst I was at the lab for the experiment, the University was holding student elections.  This was on a scale unlike anything I had seen: for a whole week many different parties of hopefuls were cooking crepes, providing massive inflatable assault courses, and serving banquets in order to persuade students to put them in charge of organising social events for the year.   No expense was spared: the students were very lucky!

As the social organising committee are called Kes here, all the parties had incorporated this into their name.

As the social organising committee are called Kes here, all the parties had incorporated this into their name.

After the experiment I headed to Iceland for a weekend getaway.  This was incredibly interesting, though bloody cold!  No Northern lights, but we saw the Blue Lagoon, Reykjavik, and the Golden Circle.  Definitely worth a visit!

New Orleans

This November I was lucky enough to get to visit New Orleans for the 56th Annual Meeting of the American Physical Society Division of Plasma Physics (or APS DPP for short!)  I gave my talk which was cool, and it went mostly smoothly.  Afterwards there were a couple of questions, including one to discuss direction of the paper, but it definitely helped to cement the theory going forwards.  Watch this space for a draft soon!

Talking about papers, since my last post my Theory paper was accepted!  (Yay!)  You can read the abstract here.

I was in New Orleans the week leading up to Hallowe’en, so there was a definite party feel!  Outside of the conference I found some time to explore a little, and had great fun at the various jazz bars in the town, as well as exploring the history of the region.

There were many houses in the centre decorated like this.

There were many houses in the centre decorated like this.

Quarter Year Catch Up

Since my last post things have been trundling along as usual.  A couple of new updates:

1) My paper has now been accepted (woohay!)  Proofs etc. need to be made and confirmed, but I have a tentative publication date now.

2) I am now actively looking for things after my PhD.  I have a semi-firm end date in mind, and now need to make sure I have some work for after the submission!  A year will pass quickly…

3) My sister graduated last week, which was a surreal, but proud, moment.  She is now doing better than me, having secured a graduation scheme within hours of graduating!

Looking very swish in her gown!

Looking very swish in her gown!

Other than this I am currently on experiment at Vulcan (so, ironically, this may make me post more) and am considering the figures for my next paper.  I am hopefully presenting my work in New Orleans later this year but funding for travel seems to be an issue at the moment…

Outside of academia, and channel-hopping, I spent a nice, though too short, holiday in Budapest.  Highly recommend visiting: cheap, interesting and good food!

A bientôt !

Well overdue update

Hello again!  It has been rather too long since I last wrote.  In the interest of brevity (i.e. in your interest) I will not go into everything I have done in excruciating detail (even though I know you were waiting for a blow by blow account of my Eurostar journey!)

Two major things have happened since I last wrote: 1) I spent a month in France and 2) I have signed for a new house in Oxford.

So I spent a month in France.  While this may seem as if it was an excuse to stay in France dressed up as work (and maybe my supervisor did have a hand in sending me on experiment there because he knew I would have somewhere to stay in Paris…) I did actually have some work to do:

  1. Bordeaux.  The first week, after a train to Paris, was to be spent in Bordeaux.  Here I was attending the HEDLA 2014 Conference (High Energy Density Laboratory Astrophysics, in case you were wondering) and was going to present for the first time at an International Conference!  This actually went fairly well, maybe because my talk was before lunch so people may not have wanted to ask questions and delay food, and we got some useful insight into the results.  Next step; write up a paper!
    The old stock exchange in front of the mirror d'eau

    The old stock exchange in front of the miroir d’eau.

    Bordeaux is a beautiful, interesting city and I would definitely recommend visiting.  I spent the weekend before the conference sightseeing, but also had the chance to explore many bars and restaurants in the conference week.  One surprising thing: all the red wine we had was crap!  As for the conference itself, it was really interesting, it was good to catch up with people and the food (3 course served meal for lunch) and conference dinner (in the Opera house) were incredible!

  2. Paris.  The next week and a half was spent in Paris or, as I’m sure my Parisian friends will correct me, just outside of Paris for an experiment at Ecole Polytechnique, or ‘l’X’ (not just ‘X’ as I found out, mistakingly saying to a friend: “J’ai une expérience à X” and him replying “You’re having a porn experience!?”.  After that I opted for using the safer word ‘manip’ to describe the experiment — as ‘expérience’ can mean experience or experiment — and used the Uni’s full name…)The experiment was a mixed bag: on one hand what we were trying to measure was seemingly beyond the reaction time of our diagnostic, but on the other it seemed to be able to illuminate some information.  Regardless, we got some data, I had fun hanging out with the other PhD students and enjoyed staying in Paris!
  3. Fréjus.  The final stint in France was for holiday.  I experienced the super-fast TGV down to the South of France and then spent a wonderful 4 or so days with some cool people relaxing, beaching, bbq-ing and exploring.  Then it was time to return to England.  (On the last I day I connected my French phone to my English to download my boarding pass: bad idea.  A flood of emails came in and I found out that at the experiment I had left in Paris they had had a little accident and damaged the diagnostic we were using…  Cue me now working to fix this!)

    Most of the group at the site of the burst dam

    Most of the group at the site of the burst dam

I was also house-hunting for quite a while since the last update, and, while it seemed at first that there would be little with the required number of bedrooms at a reasonable price, I eventually found a cool house in Jericho.  So, from mid-July I shall be moving there!  Looking forward to it, though sad to be leaving my current housemate behind (though not so sentimental about the house itself!)

Other things have also happened:

  • My paper, finally, got worked into a resubmittable state and has now been returned to the journal.   We are awaiting the outcome…
  • I have begun to work more in the lab, on both diagnostics and laser experiments.
  • It was my birthday!  I had a fun extended week long celebration with loads of cool friends and family.
The laser is working!

The laser is working!

From now on I will attempt to update more frequently, with shorter posts!  Also, still mulling over the Physics idea!

 

 

 

Theory and Snow

Whilst my last post ended on a rather optimistic note, the same cannot be said for the rest of my time in Rochester.  Though I had fun with friends on my last night, I woke up the next morning with a mild hangover and a cancelled flight…

Despite my best efforts I did not manage to get on a flight so had to stay an extra day in Rochester.  There is very little to do there, especially without a car, so I resigned myself to working and an early night (after having to find, and pay, for my own accommodation).

Spending 5 hours in the airport the next day – considering United’s track record of incompetence the previous day, I wanted to be there very early to make sure I got a flight – was a little tiring, though I had some good company via FaceTime!

I eventually got back, and in time for a second Orion experiment.  A day late, thankfully nothing had started the day before and, as it happened, nothing would happen due to laser issues.  However even this minor set back couldn’t detract from my elation at being back in England.

While I was in America, I got a reply from the paper I submitted a while ago.  There seemed to be a fair few alterations necessary, but the outlook was still positive and so I have spent much of my work time on this, finishing just last week.  It now needs to be passed by my supervisor then resubmitted, but hopefully still on my way to publishing my first paper!

Dinner was extremely good, worth going to the conference for :p

Dinner was extremely good, worth going to the conference for :p

Other than this theory work, I had to prepare a presentation for a conference held in Oxford last week.  This was quite good fun, and the dinner at Trinity was very nice.  It also gave a chance to mingle and make a few new connections!

From now on I will be working towards getting data ready for my first international conference talk in Bordeaux in May.  I’m quite excited about this, and want to do a good job, so am going to try hard at working at this data this month!  This is particularly necessary seeing as I will be in France for almost all of May, so need to be well prepared!

May has a week of conference in Bordeaux, two weeks experiment in Paris, and holiday in the south of France (Frejus)!  Looking forward to it all!

(I was thinking the other day, after reading my friend’s blog, that, although this is called a blog about my DPhil, and I do mention where I go, I don’t actually go into any detail about the Physics.  So, in case you’re interested, watch this space…)

Christmas, Orion, Omega

Hello there!  I have returned!  It has been rather a long time, I apologise, and I thought I had better make up for that.

Since my last post I have been carrying on, preparing for the second half of my Orion experiment, my paper and the Omega experiment.  However; Christmas and New Year happened also, so I shall start with that.

Christmas was fun – you all must know my stance on Christmas by now – and we had two separate meals with my Dad and my Mum.  I had also made a pledge that I would not look at any Physics until after New Year: as my previous post had shown, I was rather run down and just needed a break!  I also enjoyed New Year, which I spent up in Scotland with some friends, just chilling, walking and making bonfires (oh, and drinking gin!)

Image

Cooking and celebrating Hogmanay!

 After the holidays it was time to get back to work: the successful Orion experiment before Christmas had a second half in February, my paper was nearing submission and there was another Omega experiment.

The paper draft got finished first, with much backwards and forwards, drafting and redrafting.  Eventually submitted, I received the comments the other day.  So much for an easy ride, not accepted yet, but neither refused outright, so that’s a plus!

In between this and more experiments I also had a training course at the Centre Laser Facility on how to be an operator for the laser target areas.  This course was split into project management and safety management.  While I went into the project management with a certain degree of scepticism, it did actually turn out to be relatively useful (though how accurate the personality report was is yet to be seen!)  The health and safety aspect was, of course, a necessary evil, though the officer seemed to also take a dislike to me for no good reason…

Certified Project Managers!

Certified Project Managers!

The Orion experiment also came round again quite quickly.  There was not sufficient time between the two to change very much in terms of target/diagnostics, though we did our best (especially against some opposition!)  The experiment was very successful again, and I am rather excited and hopeful for the analysis and writing up!

After the experiment I almost immediately got on a plane to head to Rochester, NY, for another experiment on the Omega laser, which is now where I am writing this from.  Temperatures in this part of America have hit a record low of -17 C…  Which is brilliant considering I left my gloves in my other jacket…  My first attempt at leaving and walking to the shops, a trip of but 25 minutes, left me with suspected mild frostbite in my right ear and and no shopping.  Since then I have actually managed to get to places, which is useful!

The experiment itself was of mixed success, technically is worked, but scientifically not so much.  It gave us plenty to think about though, so I will likely be returning in September for the final stint in this experimental series.  Hopefully by then I will have a little more time to spend thinking about it and have a greater input.

Targets before laser fires...

Targets before laser fires…

Whilst I was out here, a few people mentioned that “With the paper and your experiment, surely you have enough to write up now?”  Which is both encouraging and terrifying in equal measures!  I am massively uncertain about what I would like to do after I finish – that is not to say that I don’t have ideas, just which is the right one is hard to pin down – so finishing early may be of use, but I also don’t want to rush to finish.  I love living in Oxford.  I have found my enthusiasm for physics again.  I enjoy the various places I am sent to (which may include in more exotic locations, watch this space!)

I shall be sticking around for a while longer I think :).