Halfway

A day is just not long enough for everything I want to do.  So blogging got pushed back to this evening.  Okay, let's see...work.  Yesterday I showed Mélanie my threshold results.  She suggested I look at one more cavity, and also make "movies" of consecutive single-pulse spectra using the spectrometer software.  So I did.  The movies aren't really movies, just 30 or so spectra in a row.  The shapes are pretty consistent, though I would hesitate to call them "lines" or "peaks."  Oh, I got to do a calculation!  Hurrah! Since I've empirically determined the threshold of the 160 micron true Fabry-Perot, I can calculate the expected line width of a 140 micron FP cavity.  My observations do not agree with my calculations at all, as they simply do not include a threshold, but I'm hoping that's a result of the new-ness of this sample and that things will settle down when I retake the data.

Today the lab was rather empty.  A lot of the students and professors went to a picnic hosted by another lab group, and Mélanie wasn't in either.  I began a fairly systematic investigation of the stability of the tilted cavities - that is, I'm looking to see how much the spectra change when I make a small translation or rotation of the stage on which the sample rests.  We tentatively expected the spectrum to change as the pump laser was directed at different portions of the cavity, since the width is different at every point.  I spent quite a while aligning the sample very carefully and taking reference spectra with the 160 micron true FP.  It's reassuring to note that features I had previously observed still hold true; for instance, the pump position long-ways along the laser doesn't really matter for real Fabry-Perots.  I was pleased to see something interesting in the tilted spectra, though.  When pumped at the very end of the long cavity, the spectra of the cavities I saw looked like typical spectra, not messy like the spectra from the middle of the cavities.  I still have to show Mélanie and look at the really tilted cavity, but it's cool.  I think that this pump position only pumps the very tip of the cavity, over a length where the width doesn't change significantly.  I can't tell much from Fourier analysis yet because the tilts I've examined are too small to tell path lengths apart.

So that's been work.  It's difficult for me to believe that I'm halfway done with this internship.  That also means I'm halfway done with my stay in Paris.  While the time is flying by, I don't feel that I'm wasting it.  My life is quite full right now.  By day, my mild-mannered alter-ego works in an optics lab.  But by night, my...same mild-mannered persona...has adventures in the city!  Last evening's quest was to the Musée d'Orsay with Linda, following a restful picnic in the Tuileries where we were joined by Caleb and Mir.  Caleb brought five (delicious) baguettes, I brought strawberry jam and cookie butter, and life was good.  The Impressionists were good too.  They are the only school of art about which I know much of anything, thanks to Madame Bettis and French 5 in high school.  At the beginning of all these museum visits, I thought I would probably find other groups and painters I preferred, as it would be unlikely that the one school I know turns out to be my favorite.  So far, though, I remain loyal to the Impressionists.  Their paintings are pretty.  There are others I quite admire as well, but I spend the longest on the Impressionists.  By now I've almost made it through the whole upstairs gallery at the M 'O.  One or two more visits and I'll be able to look at some of the other wonderful things in that museum!

Tonight was partially an evening of rest.  I needed it.  Kierstin and several others have gone to a music festival in the city of Arras, about an hour away by train.  I'll have the room to myself for the next week, since she will be in the UK for work immediately following the festival.  Weird.  I suspect I'll get rather lonely.

The fun treat this evening was my visit to the famous bookstore Shakespeare and Company, tucked away right next to the Notre-Dame.  I browsed for an hour or so, and almost regret that the building was so crammed with books that I couldn't see half of them, as they were on shelves up to the ceiling, far over my head.  And I couldn't resist buying myself a few souvenirs - what better place to read Dickens' A Tale of Two Cities than Paris?  Er, besides London, I guess.

Here are some odds-and-ends photos from the past few days: a bit of Cachan (on the walk to work), the outside of M 'O, lovely Paris, the metro, and the bookshop.  If things go even approximately well, this weekend should generate some good posts.  I have plans!

Just another Louvre Wednesday

The presentation was informative, and the free lunch afterwards put all American buffets I've experienced to shame, so my time at Ecole Polytechnique was well spent.  I arrived back in Cachan around 2:30 pm and spent about three hours fiddling around: I revised my line widths summary, polished up my threshold analysis, and took some spectra of a yet-more-tilted cavity.  These I might redo tomorrow morning, since the new cavities take a while to settle into a particular response when pumped.

I hurried back to the dorms after work and ate my baguette sandwich supper, then met Linda and set off for the Louvre.  The museum is much less crowded on Wednesday evenings; maybe it's less-than-common knowledge that it's open late, though I don't know why that would be.  In contrast with last week's statues, we opted for the vast collection of French paintings on the second floor of the Sully wing (it may have spilled over into Richelieu; I'm not sure).  Some of the paintings didn't quite speak to me, sure, but the ones that did more than compensated.  Here is a reason to carefully prepare oneself before entering the Louvre:  one can walk innocently into a room and this painting is. Suddenly. Right. There.

That's Renoir's La Lecture, and I could stare at it for minutes on end.  I did exactly that, as a matter of fact.  Why can't the colors look the same through my camera as they do in person?  You don't know, you really don't know what it's like unless you're there.  Renoir's skin tones incorporate every color of his palette - pinks, to be sure, and reds, but also blue and yellow and green and violet - what would be a bruised mess in any other hands becomes an ephemeral, softly-radiating vision of tranquility.  Even Linda, whose aesthetic tastes tend towards hyper-realism, admitted that this "fuzzy" painting catches the eye from across the room.  I could hardly bear to move on to other rooms.

But I'm glad I did, because we had quite a nice time browsing and being amateur art critics.  The next-highest-point of the evening was the discovery of a small room of paintings by an artist unknown to us, but whose paintings we both really enjoyed.  Claude Lorrain painted several scenes of ships at sunset, amidst classical architecture lapped by the ocean at its base.   For some reason, this particular collection of elements is idyllic as far as I'm concerned.  We lingered there for a while.

We lingered for much more time in room displaying Rubens' Medici cycle.  I'd heard his name before, but knew nothing of his work.  I still don't know too much, but at some point he was commissioned to paint a series of 24 huge works for the Luxembourg palace, and now they are all in a room in the Louvre.  Each one should have been the work of a lifetime, I feel, and yet they just keep going.  Linda and I sat on the well-placed benches in the middle of the room and just soaked it in.

We didn't see nearly all of the French paintings, but there's next week, and the next...The Louvre is a wonderful place.

On the way home, we went and got some more world-famous macarons, because why not?  Yum.

And for tomorrow: le Musee d'Orsay.  So much Renoir.  I can't wait.

Macs and French keyboards

Look at this - a blog post in the morning!  Shouldn't I be at work?

Today the Ecole Polytechnique is hosting a talk about the master's and PhD programs that they offer, so I'm all the way out at Paliseau waiting in Linda's and Drew's office.  It's about an hour commute, and the campus is vast, so I knew I wouldn't be able to locate the talk on my own and tagged along with them this morning.

While I wait, I can fill in the details of my work yesterday.  Iryna needed the optics room in the morning for some last-minute data collection, so I chugged through the spectra I took yesterday, searching for lasing thresholds.  It was an Igor adventure.  I plotted each spectrum in turn and zoomed in on a particular peak to check its amplitude.  While I was looking at the reference cavity, a true Fabry-Perot, I could fit the peaks to nice Gaussians, but the spectrum goes all weird and jaggedy as the tilt angle increases, so fitting to an analytic function was out of the question.  Instead I just recorded the maximum intensity of the test peak as the pump energy decreased.  It occurs to me now to check whether there's a significant diference between the Gaussian-fitting method and the maximum-amplitude method, using the true FP.  I doubt that there is, but it would be good to make sure.

Anyway, I generated three plots of amplitude vs pump energy, and it looks like the threshold increases with the tilt angle, though I still want more data.  I always want more data - perhaps this isn't necessarily a good thing.  I've certainly noticed while taking the data that the energy needed to begin seeing a spectrum at all, even if it's a fluorescence and not a lasing spectrum, increases with tilt.

I did get the chance to take threshold data for a new cavity right before I left work yesterday, so I can add that to my plot.  This afternoon I hope I can finish up with my little threshold investigation for the time being, and tomorrow maybe move on to the pump position questions.

In the evening, I met my friend Eric, who has been traveling around Europe for the past month as a celebration of free time before beginning grad school in the fall.  He's in Paris this week.  We wandered Le Marais for a while and found a pretty good restaurant, where I was entirely boring and ordered a chicken sandwich.  It was a tasty chicken sandwich, at least.  Then more walking and talking.  We ended up by the Pantheon, having heard some very good street musicians and eaten delicious Berthillon ice cream along the way. Quite a pleasant evening.

Today is Wednesday, so several of us are planning on visiting the Louvre. Stay tuned to (hopefully) hear about some more incredible works of art!

Progress or something

I'm writing back-to-back posts, this one about my time at work today.  Thankfully, Mélanie has returned and is feeling much better.  We had a bit of conference this morning, and I showed her the summary I wrote last Wednesday and the path-length calculations I had finished.  She was quite intrigued by the spectra showing an abrupt and dramatic change in the qualitative shape of the spectra for the 160-159um cavity as the pump energy approached the lasing threshold.  (The two numbers refer to the widths of the cavity at either end of the strip, so the 160-159um cavity has the smallest angle of all the non-parallel FP's.)  The spectra change from looking "typical" for true Fabry-Perots to bumpy and funny-looking right around the threshold energy.  My new directive: investigate this region and determine roughly how the spectra depend on pump position and energy.  Pump position will likely have a large impact on the spectra with these new cavities, because their width changes from top to bottom.

I haven't quite begun to tackle my new task yet.  Today I took more threshold data, and managed to determine the lasing threshold for a true Fabry-Perot, as a reference.  Over the past few weeks, I have not been accustomed to seeing what I expect when I plot my data, so I was very pleased to see the quasi-hockey-stick shape that clearly heralded a threshold energy.  It takes a while to churn through this data, so I still have three more cavities to analyze before moving on, but I feel purposeful and optimistic.  Secrets of non-parallel Fabry-Perots, I'm coming for you!

Rhinemaidens plus paparazzi

Well.  Germany happened this weekend.  It was quite an adventure, and an enjoyable change of pace from life in Paris...even for only forty hours or so.

Waking up at 4:00 am is generally not the most pleasant thing in the world, but Kierstin and I had packed the night before and were all ready to go, even up to the peanut-butter-and-jam challah sandwiches we cleverly wrapped to eat on the train for brunch.  We met Mir and Linda and headed out to catch the first RER train of the morning to Gare du Nord.  Mir had his camera ready, and I mostly relied on his outstanding documentation for photos this weekend.  Unless otherwise noted, any photos in this post are the work of Mir Henglin, photographer extraordinaire.  (As always, check out his blog for many, many more.)

We made it to Gare du Nord with time to spare and tickets on hand.

The train was very comfortable - I understand now why the ticket was rather pricey.  It's rather strange, though, because of course we opted for the least expensive tickets, and I wonder where the economy/coach trains are.  Do they still exist?  At any rate, we snuggled into the large padded chairs, arranged our belongings in the bins overhead and on the fold-out tables between our pod of four seats, and alternately watched the countryside roll past through the huge windows and slept.  For whatever reason, our train was delayed several times and sat on the tracks, delivering us to the Cologne Hauptbahnhof almost an hour behind schedule.  There were stops in Brussels and some German cities.  I suppose now I've been to Belgium too! I've seen it through the windows of a train.

Upon our arrival in Cologne, things got a bit dicey for a while.  However, we made it onto a light-rail train headed for Hersel relatively quickly, and even managed to purchase train tickets shortly afterwards.  It was past noon when we arrived in the small town of Hersel, about fifteen minutes outside of Bonn, where Linda's host-mother of sophomore year lives.  Walking through the narrow streets, reading the German street signs, enjoying the sunshine, I began to feel like things were under control again.

My relief was greatly increased once we made it to Linda's old house and met her host-mother.  Sabine is an inspirational person; there's no other way to put it.  She spent decades in her youth working on humanitarian projects in Africa, lived in Paris for a time, and now paints, and hosts international students almost continuously.  Her house and studio have a bright, cheerful, tranquil quality about them that I've only ever encountered in a few other homes.  She put us at ease immediately, and fed us a brunch of breads, spreads, and cheeses that had Mir laughing with happiness.  (That was when he first bit into the sugary, raisin-y pastries.)  We are extremely fortunate people - staying with Sabine was the best possible way to visit Germany, as far as I'm concerned.

After brunch, we caught the train into Bonn, where Linda's old friend was patiently waiting at the station to meet her.  They had planned on an afternoon together, so Kierstin, Mir, and I saw the Beethoven house and museum while they ate currywusrt and got ice cream.  Kierstin is a classical singer and a music lover, and she very nearly swooned upon her first sight of the house in which Beethoven was born and raised.

Then we wandered the streets of Bonn.  It's a small city, and old, and quiet, and full of history.  It was the capital of Germany before the reunification, you know.  I quite liked its cobbled streets and tall churches.  We looked around at least three churches, and an open air market, and saw what I guess was the old capital building, and passed a pleasant afternoon.

Then it was time to see the Rhine!  Oh boy, the Rhine.  I was very enthusiastic, even though I know almost nothing about the history of the area.  But the Rhine is famous, and also important.  Turns out it's a lovely river in its own right, too.  So we walked to the riverside, and across a bridge.  On the way we passed and were enthusiastically greeted by several happy, questionably-sober men pedaling an absurd contraption up the street:

Leave it to the Germans to build a bar-bike...We took another train to Konigswinter, a nearby town on the Rhine, and walked along it for a while.  (We meant to go up the mountain to visit the ruins of an old castle, but it was too late in the day.  Oh well.) After a dinner in town, where I was not-too-adventurous and had bratwurst and fries, it was time to go home and sleep.

Sunday began on a wonderful note, with another delicious breakfast and a stroll down to the Rhine a few minutes' walk from Sabine's house.  The river had actual banks at that point, instead of being channeled between walls as it was near the city, and we waded, hunted for Rhine stones, admired the views, and thoroughly enjoyed the river.  Mir and Kierstin plunged right in and went for a quick swim.  I stuck to the bank, but still was very happy.  After spending several weeks in cities, it was a relief to stand quietly on the bank and listen to the lapping of the water.  Shorelines are some of my favorite places.

Here we are, the three Rhinemaidens of Kierstin's beloved Ring Cycle, recorded by the Amazing Mir:

But we weren't done with Germany yet!  Sabine drove us to Bruhl, where we toured an opulent manor house built by some archbishop or other.  It was quite impressive - in all honesty, I enjoyed this tour rather more than my rushed and crowded whirl through the Versailles palace.  Then it was time to bid farewell to the inspirational Sabine and catch a train back to Cologne.

I haven't mentioned it up until now, but when one exits the main train station in Cologne, one is immediately stricken with awe and astonishment.  This is entirely due to the Dom Cathedral, a marvel of the medieval times and a structure which must be seen to be believed.  I had thought Notre Dame was built on a staggering scale...in fact, Kierstin's initial reaction upon glimpsing the cathedral would have satisfied its builders: "Oh my god."

So we walked around it, and walked inside it, and admired.  (Today, Monday, Kierstin and I read the Wikipedia article linked above and fully realized what savvy tourists we unintentionally had been.  My goodness.)

Dinner and a visit to a shop in the station for German chocolate filled the time until our train left.  Due to some quirk of scheduling, the first-class tickets for the return trip were only three euro more than the cheapest tickets, so we had a grand ride back to Paris.  Snacks, tea, wi-fi, and four contented students.

La Fête de la Musique

The work-week wrapped up quietly this time.  Mélanie hasn't been in since Tuesday - I'm not sure what sort of bug she has, but I hope she feels better soon.  Now at least she has the weekend to recuperate.  Fortunately, I have a sufficiently long list of things to do that I can carry on in her absence.  The limiting factors during the past few days have been my inability to properly set the x-scaling on my Fourier-transformed waves without assistance, and the availability/functionality of the optics room.

Okay, what have I accomplished?  With the help of Clément, my Fourier-transform code in Igor spits out lovely optical path length calculations.  I've tested it on three typical Fabry-Perot cavities of known width, and the results agree with the nominal width to within a few percent, the accuracy also reported by the group in their 2007 paper on the topic.  So my code is probably working properly.  The regular FP's have lovely, evenly-spaced peaks in path-length-space, corresponding to light that travels twice the width of the cavity (by reflecting once off the side), four times, six times, and so on...the amplitude of each successive peak decreases, indicating that the once-reflected path is the dominant one.  So far so good.  When I start looking at the non-parallel FP's, things go a bit wonky.  All the amplitudes decrease, first of all, indicating that the poor little microcavity is having some trouble lasing.  Some multiples are skipped...I'm not really sure what's happening.  Mélanie will save the day!

I'm also supposed to be investigating the lasing thresholds, by tracking the amplitude of some particular spectral peak (not the transformed peaks) with increasing pump energy.  I've taken a fair amount of data, but have yet to fully analyze it.  By virtue of not falling asleep while taking data, I've already noticed that the threshold is increasing as the angle of the sides increases.  This seems sensible enough.  Stay tuned for more exciting discoveries!

Yesterday happened to be the longest day of the year.  Happy solstice!  Et joyeuse Fête de la Musique!  Apparently there's a tradition (a summary is here) of an evening of music everywhere in Paris - ensembles, bands, street musicians, professionals, amateurs - everyone sets up shop anywhere and everywhere and plays all night.  The other students in my lab group talked about it all week, and several of the REU students made plans to walk around downtown and hear what we could hear.

I was rather worried when the hail started in the afternoon.  But it turned out that Paris was just getting the bad weather out of its system, as the evening was gorgeous.  With Mélanie's emailed permission, I left work a few hours early.  Kierstin and I headed out to find the Pantheon, to see it and to look for the Celtic musicians I promised, having looked over some handy websites earlier.  We never found those musicians (I learned later they were nearby but not actually at the Pantheon), but had a pleasant walk.  Kierstin, who is madly in love with Proust and his search for lost time, went into raptures of delight upon discovering and purchasing a macaroon cookbook from a bookstore named Le Temps Retrouvé.  So the quest was successful in its own way.

Then we took the RER one stop north to the Denfert-Rochereau area.  There was a huge stage set up near the station, but no bands yet (though they were piping in music that I recognized from my childhood).  I really like this area of the city.  It's almost in the heart of the city, but it's more residential than touristy.  It feels real.  So I was perfectly happy when we decided to walk from there to Notre Dame.  Maybe an hour and many map-consultations later, we made it!  All roads lead to Notre Dame in the end.  We were just in time to meet Mir, Josh, and a large international group of students from their lab.

To shorten a story complicated inevitably by the dynamics of large groups, Mir, Josh, Kierstin, a late-arriving Margaret, and I wound up wandering the streets listening to various groups.  There were some very good drummers by St. Michel, a brass band in the street behind them, an amateur rock group who sang in German, some soulful guitarists...everywhere there was music.  And so many people!  Despite my general dislike of crowds, I had a great time.  And I ate a cinnamon-sugar crêpe.  Yum.

The highlight of the evening was Josh's own saxophone performance.  We found a quiet place right down by the Seine and he gave a concert that it was a pleasure to hear.  Though there wasn't much foot traffic nearby, the myriad sight-seeing boats cruising up and down the Seine were a prime audience, and the passengers applauded him as they passed.  Way to go, Josh!

The public transportation ran until 5:00 am last night, but we made it back to the dorms around midnight.  If you had asked me a year ago - a few months ago even - I never would have guessed that I would spend this summer solstice listening to street music in the heart of Paris.

This evening has been quieter. Mir, Kierstin, Linda, and I leave for Bonn at 6:00 tomorrow morning!  So no posts for a few days, but I hope to have many exciting adventures to report after the weekend. 

A lundi!

La vie en rose

Let's see, work today...Mélanie wasn't in, so I attempted to muddle along.  There were problems with the power meter that tells us the pump energy, so that rather put a damper on the work in the lab for a while.  I'm still not sure what was wrong or if it will happen again, but the meter started working abruptly around 5:00 pm, so hopefully all is well again.  (Incidentally, I've been having to nurse the pump laser along when I go to start it up in the morning.  I really hope it doesn't have serious problems, since that would basically shut down that portion of the lab while it was being fixed.)

So instead I spent the morning TeXing up a brief report of my investigations into spectral line widths.  Turns out that those optics lab summary reports Prof Haskell required were good practice after all.  In the afternoon, I returned to the new issue of taking Fourier transforms of spectra to infer optical path lengths inside the cavities.  Well, it's a new issue for me, but the lab group is quite familiar with the process.  After (figuratively) banging my head into a wall for a few hours, it dawned on me to ask Clément for help, and he explained what I needed in the space of a few minutes.  So tomorrow I should be all ready to analyze!  All in all, it was rather a slow day.

In the evening, Kierstin, Caleb, and I were all set to visit the Louvre, but it was such a lovely evening that we wandered in the Tuileries for a while...which became a quest to see the obelisk at the other end of the garden...which became an exploration of the other huge roundabout at the other end of the Champs-Elysées...which turned into an investigation of a side street and neighborhood...which briefly turned into a determined search for a public restroom (0.50 euro in the Tuileries, but quite a fancy, well-kept public restroom)...which then became an adventure crossing the Pont Alexandre III and the discovery of the Grand Palais and Petit Palais...

...we never quite made it to the Louvre.   I'm not upset.  There are several other weeks, and this was by far the most pleasant evening-weather we've had here so far.  Much better to spend it outside.  Additionally, in the end we fetched up by the macaroon place again, so I treated myself to that cherry-blossom one that looked so good last time.  (I found pictures of them here, if you're curious.)  And it was as delicious as it looked.  It was a satisfying evening of adventuring in Paris.  I still am amazed by the sheer ubiquity of marvelous monuments and grand views in this city.  Nearly every cubic centimeter is a treasure.

Oh, it's been a few days now, but I saw this event begin while walking around Notre Dame last Thursday evening.  I had no idea what was going on, but it looked fun.

Kierstin and I have unintentionally adopted a theme song for the week: Edith Piaf's La Vie En Rose.  It's been stuck in both our heads for the past two or three days, and bursts out occasionally in fits of humming or, in Kierstin's case, beautiful singing. No complaints from me.