A different kind of excitement, 19th July, 2009

"Excuse me," Bulbul said, "my friend wants to take a picture with you." He had not even introduced me, nor given me the chance to say 'Hi,' but here he was, getting my camera ready to take a picture with a lady I had never even met. We were in a small enclave of concrete, in the 'not the most well lit' of settings, and she looked a little bit dazed, as if she did not know what was going on. I tried to squeeze in an introduction of myself, telling her my name, and holding me hand out part way, so that she would notice, and shake hands if she was accustomed to that, but would not feel obliged, since my hand was not fully extended. It could just have been me, but I thought I saw her pull back her right hand, a tiny little bit, in case I came across as too forward about shaking hands. On a side note, it was all good that she did not shake hands. I mean, let's face it: we're boys... girls let us shake hands, we want a kiss; girls let us touch the cheek, we want a hug, girls let us give them a hug... well, we're boys.

I had only seen her, a few minutes before, dancing on the stage; and only just found out that she was an actress in Bangla movies. Thankfully, Bulbul needed no introduction there, backstage, since he was one of the organizers of the show. She was approachable, of course, and she was willing to take a picture. I found it a little bit surprising that this lady, who seemed to pull her hand away only a few short seconds ago, now moved in closer to me than I am accustomed to, very nearly putting me on the defensive. Maybe I have an over-inflated view of my personal space.

We took turns, taking pictures with her (we took a picture, each), and then we left her to relax, after what I am sure was a grueling day. On the way back, I realized what we had just done. We had walked up to a lady, and effectively said "Dekhi-to, dekhit-to, shundori-ta sha-they chobi ni-te dey-naki dekhito!" (Let's see if this dame lets me take a picture of her, with me). To be more politically correct, we had effective said "Apa-moni, apa-moni, apna'r sha-they akta chobi nei, dekhito!" (Let's see if this lady lets me take a picture of her, with me). It wasn't that I had felt very certain that a lady who was recuperating (catching her breath) from her last performance would have acquiesced to two strangers (well, one of them not a complete stranger) wanting fan photos with her. I was not sure she would have balked, either. At the time when Bulbul had asked her for to take those pictures I had felt a certain kind of uncertainty, that things could go this way, or that; and hence, the excitement. It wasn't that I had been standing at the edge of a precipice, deciding whether or not to jump, nor was it that I was skiing down a hill at high speed, deciding what move I would use at that next crest, it was just that uncertainty. It was an uncertainty about the reaction of a human being, a reaction that could have gone this way, or that, but could be heavily influenced by that guile of the asker/requester. The very realization that we had steered a human being's response, albeit so mundane a reaction, was enough to give me an adrenaline rush, for I am more accustomed to seeing this sort or steering in work related circumstances, than in social circumstances. That little, minuscule event finally led me to understand the joy that some guys get at approaching random girls, and asking to take a picture with them. It's not that I would want to go around town, and try to take a picture with every pretty girl I run into, just for the sake of a whole hoard of pictures, but the challenge of taming probabilities is enticing. Of course, let's not treat human beings the same way that I treat sheer rock faces and smooth skiing trails. The latter are stuff to be conquered, but the former are human.


The following is a collection of short clips taken during the show, a concert of Bangla/Bengali songs, in Queens, NYC. Pardon the sound quality: I had not known that my digital camera would stop recording sound while zooming in and out. The concert, itself, was held on 19th July, 2009.



Here are some of the pictures from the event:

























This lady said she drove 22 hours, from Dallas, to see this event.




My friend, Bulbul, and I took photos with the performers, ourselves:

Yeah, the above lady is the one I mentioned when I started writing this post.
















Wow, these two, above, certainly posed the same.



P.S. I really liked the chorus of the track "Roopban nache komor dulaiya," which the actress danced to, at the event. The closest version that I could find to that soundtrack is located here, though I am not a fan of the kind of dance shown on this video (which is why I did not bother to embed it).

In keeping up with my sports, 17th July, 2009

I have not been doing a lot of free running stuff, lately. My right hip joint is partly to blame (besides my climbing training), since I have been having problems with it since I over strained it (if there is such a word) last February, while indoor climbing.



So, right now, holding a horse stand can be a challenge, without a proper warm up, though I still practice it everyday:


I also train for the side split, every once in a while:


Yeah, if you're wondering, the silly little video those two frames came from is here:

Clearly, I have not let my hip injury keep me down, too much.

Anyway, these days, while I have not been doing my v-sits, too much, nor have I been persistent at the back bridge (I sure need to get back into those), I have been doing my pull ups every other day. In the 'off-days' I have been doing my push ups. Since I started doing pull ups, some time around May, I have been gaining weight dramatically. Whereas I used to loose about 1 Kg (about 2 lbs) a month, I have gained about 6 Kgs (13 lbs) since last April. At first, I thought I was uncontrollably gaining weight (and I could not pin point the cause) but when my friends told me, a few weeks ago, that I looked fitter than I did last January, I decided that my weight gain was due to muscle gain. Of course, I was not too happy about this, either, since a climber needs to be as light as possible.

Perhaps I should not be too concerned, because even with my current muscle gain (if, indeed, the gain was all in muscle) I could still be down to 118 lbs (54 Kgs), soaking wet (to borrow the words of Marcus Luttrell, author of Lone Survivor), or lighter, if I trim down some. Of course, right now, I am acting out on my concerns: rather than do active v-sits and pull ups, for the past two weeks, I am doing v-sit holds, and I am hanging myself from my fingers. Perhaps the finger hangs will come to some use, in the future.

So, while my free running may be on hold, my climbing abilities should be improving. Just a few days ago, I went with my friend, Francis, to the river side, just near my school (we needed to clear our heads, after a long day). While on the river side, I got comfortable moving around rocks.





We then proceeded to the park area, where we could go hang ourselves. I mixed finger hang holds with finger pull ups. While I was happy that the bars at this place seemed to exercise the muscles on the top of my fore arms, I was not too happy with how little exercise my thumbs were getting. I was also a little frustrated about not being able to practice my crimp hold too much, since the bars were a little high, for me (we went there, yesterday, too, and since I tried the crimp hold later into the session, and found it harder, next time, I will try it just as soon as I am warmed up). Nevertheless, it was a good workout.



It left my fingers unable to hold on, though I did not feel any soreness. My upper body did not feel exhausted, either, but I know that breaking the discipline, and overworking myself will only result in injury, and my temporarily being out of commission.

I even got Francis to try doing some pull ups.



Heh heh heh! Like I say: "You don't choose what happens to you, you just choose your friends. Your friends decide what happens to you. When you have friends, things happen."

Of course, I have not stayed away from free running, entirely. For the last two days I have been trying (and failing, miserably) at hollowback presses -- I cannot seem to arch my back, once my feet get off the ground. My pecs are a little sore from my attempts. Other than that, while I have not been trying any more butterfly kicks, for fear of exacerbating my right hip joint injury, I have been trying butterfly kicks, once in a while. I might actually have improved, a bit: if you look at my video from May



and compare it with a video from a few days ago



you might notice that my legs go up a little higher. Of course, I must point out that this might have been due to my reaching my trailing hand backwards (so, I cannot tell how I will perform, once I put one hand after the other, like I used to), like Damien Walters, in his video here:



I shall hope to be able to continue with climbing and free running training, in parallel. Maybe it is a good idea to train the fingers, one day, and do push ups, v-sits, squats, and bridges, the next. Hey, they do their day job of keeping my frustrations at bay!

Z-Scan: No Sense Suffering in Silence, and Dying in Pain

Okay, so, after talking to my professors, I (with Francis) have cleaned the laser's (PY61C, from Continuum) guts with fresh dichloroethane, put it into free run, made sure the acousto optic modulator was working as it was supposed to, optimized for amplitude inside the laser cavity without the aperture, then with the aperture (though I probably only found the local maximum in both cases, rather than the global maximum -- bummer), then stabilized the laser. I then (with Francis) put in the laser dye (Q-Switch I, from Exciton) at 0.98kV on the oscilator (which is 2 notches above the 0.94kV on the flashlamp for the lasing threshold) and killed the extra longitudinal modes, but we could not see anything on the digital (or analogue) fast osciloscope. So, we increased the oscilator voltage higher, and higher, killing off the new longitudinal modes using more laser dye, until we got the gaussian pulse train (per flash of the laser's flashlamp) to be bright enough to be detected by the electronics of the digital fast osciloscope. We then put more dye until only 8-9 pulses were left in the gaussian pulse train. We then turned down the voltage supplied to the oscilator's flashlamp until we got no lasing, and turned it up again. We found the lasing threshold to be 1.04kV, and we went two notches up, as instructed, and set the oscilator's operating voltage to be 1.08kV. At this point, we still had 8-9 pulses on each pulse train, on our 20Hz Nd:YAG laser system. We then played with the timing of the gate on the Pockel Cell, and got a stable beam dump laser output (energy fluctuation was within plus/minus 10%).

Now, here is the path of the laser:

Z-Path_1
Originally uploaded by faisal_halim

The blue part shows the path of laser after exiting the laser housing (inside which also reside the laser amplifier and the second harmonic generating KDP crystal), the green part shows how the beam is moved to the other end of table, and during this part the laser beam is attenuated to meet the experiment's requirements, and the red leg of the journey shows the part of the beam used not just for taking beam energy readings (see the energy meter's reading head to the top right of the red leg), but also the z-scan readings.

To align the beam the mirror at the blue-green intersection is moved until the beam hits the first aperture on the red leg dead on, and then the mirror at the green-red intersection is moved until the beam hits the second last aperture dead on (we try not to touch the last aperture, as its diameter will effect our scan results).

Now, all the alignment assumes that we have a gaussian shaped circular beam (this is accomplished by tuning the laser cavity properly, and then by carving out any unwanted portions of the beam using the first aperture in the red leg of the beam). If we have a TE01, or a TE10 beam, then we are not to use such a beam. A roughly circular beam may be carved into a more circular beam (if it has a halo of some shape, to one side, then that may be carved out, too), and used in z-scan experiments. At first, we kept getting what looked like a TE01 beam,
(see: My z-scan is still misbehaving)
but it turned out that that problem was caused by a faulty polarizing filter (in the green leg), which I promptly removed.

The problem that we are facing, right now, is that while our beam looks circular, it also looks like most of the energy is concentrated along a crescent along one edge of the beam -- kind of like when you can see a crescent moon, at night, but can see a halo like glow that betrays the existence of the whole of the moon's disk, though, I exaggerate. So, no matter how well we align the beam, I simply do not think that we will get a z-scan (and, right now, we are not getting a z-scan). So, while I am not sure what exactly I should do, I am thinking that I should go back to the laser, optimize the laser cavity (finding the global maximum of the peak beam intensity, for all the possible back mirror positions), then put in the aperture, and then scan through all the possible positions to find that global maximum for the photon content of the cavity, and then, hopefully, I will have a beautiful, gaussian, laser beam.

Another, perhaps crazy, idea that I am having is finding another aperture (smaller than the one we are using inside our laser cavity), and taping it over the current one -- or, maybe, I can talk my professors into buying a smaller aperture, at a later time.

I am sure that my problem with the notorious crescent is not something new in the field of z-scans -- the technique has been around for a while, now, so I am sure I am not the first person to encounter this problem. While I have not found any blogs, or stories, by anyone who has solved this problem, I am hoping that when I am done with this issue my story will benefit those who have this problem after me. No sense suffering in silence (keeping the world in the dark), and dying in pain (perishing, by failing to publish)-- there is no sense in playing the MIBs (or anyone who gets in, gets the job done, and leaves without a trace, with no one knowing that he/she was even there) from the Will Smith/Tommy Lee Jones movie Men in Black. Afterall, as a scientist, you are really a part a whole much larger than yourself, and your own private dreams. As an engineer, or a scientist, you have the rest of your team, or community, actually depending on you, rather than just waiting for the job to get done, without a care for you (yeah Ejovi Nuwere, author of Hacker Cracker, is a real inspiration). It makes much more sense to be heard, and helped, if only to help someone else.

Z-Scan: My z-scan is still misbehaving.

My z-scan is still misbehaving. I have been given a deadline of Monday morning (13th July, 2009) to submit the results of the z-scans that I have been asked to do. Each time I think I have made progress, however, it turns out that I have left something out. One time, I forgot one of the system checks, another time I forgot to put a lens back, another time I had trouble realigning for a different wavelength. So many challenges, trials, and tribulations. O well, more later. Work now.

• Just so you know, a z-scan is an extremely elegant optics technique, used for measuring two photon absorption (take that, my high school physics teacher!) and intensity dependent refractive index change of materials.

I am back, for a few minutes. You see, this is the second week running that I am doing this experiment, and it turns out that I had had quite a few of the fundamentals of a mode-locked Nd:YAG laser misconceptualized. I had thought that in order to get such a laser working (ours is a dye laser) you have to set up the oscillator (the back mirror, the beam path length altering prism, the acousto-optic modulator, and the aperture need to be properly set), pump it with the appropriate level of power, then put in the q-switch dye, and then adjust the back mirror and prism while the laser's Pockel Cell was turned on. O, how I was wrong! If you try to get a stable reading for the energy scattered from the laser while the Pockel Cell is in action, then your experiment will be in a state of inaction, and you will be in a tensed state of hyperactivity; which is why I spent 36 hours to take a few z-scans last November.



As it turns out, you first get the laser to start lasing at its threshold (or higher, depending on your needs), align the optics, then increase the laser oscillator's flashlamp voltage (we have a Continuum PY61C laser) by two notches. You then kill all the transverse modes, using the laser dye, and use the back mirror and prim (adjust their orientation and position, respectively) to stabilize the amount of light being scattered (you can observe this on a slow scope, or even on a fast one). You then turn on the Pockel Cell, and change its triggering photodiode's sensitivity, the cell's gate timing, and the orientation of the in cavity half wave plate to dump a fixed portion of the Gaussian pulse train in each pulse of the 20Hz laser. Using this two step approach we get a very stable output from the laser. Well, guess what, my buddy and I (both of us have been working on z-scans for some time, now) finally grasped that only last week. In case you are curious, to the left is what our laser looks like.



Of course, that was not the end of our troubles: my partner in crime (Francis) and I (hey, don't look funny, holding up the experiments does feel criminal, no matter how inadvertent) still had to learn the proper, practical way to move a laser beam. This picture shows the optics:





















The laser beam that comes out of the laser housing has to be reflected by a series of two mirrors, so as to shift the height of the laser beam, while making sure it goes parallel to the surface of the optical table, even if the beam was not parallel to this surface when it exited the laser housing. For this, the simple (and naive) rule is that you use the mirror close to the laser housing to align the beam onto the center of an aperture held just after the second mirror, and then use the second mirror to align the beam onto the center of the aperture that will be closed if you are doing a closed aperture, intensity dependent index of refraction experiment. Of course, we know that when one mirror is moved, then fine changes have to be made to the other, so I use both the mirrors to align to the center of the first aperture, and then I use both the mirrors (sequentially, again) to center the beam onto the second aperture. I feel that we do a more effective job, this way.

_____________________________________

Okay, the fire alarm is going off: Sunday's annoying tests.


















That means I cannot run z-scans for the next half hour, oso (or, maybe, an hour). I can check on the laser's stability, during this time. So, let me show you what I have done in the meantime. Since before last night, Francis and I noticed that our beam profile looked like this:



















Now, I spent the whole of last night trying to get a TEM00 beam, but in vain. So, I decided to turn the laser green (using second harmonic generation), then align the optics so that one of the lobes gets cut off by the aperture, while the other is used to approximate a TEM00 beam for the z-scan:


Of course, that fire alarm went off before I could verify that what I was doing would give us good z-scan results -- that flashing fire alarm could throw off my readings.

The idea is that if I can get away with doing the experiment this way with green light, then I can also do the same with infrared light. Now, let's just hope that this works!

________________________________________

AAAAAAAAAAHHHHHHHHHH!!!!!!!!!!!!!!


In the past half hour, my laser's output power has consistently drifted down! No wonder my z-scans are coming out bad.

________________________________________
It's Monday, the 13th of July, 2009, now. The laser has been VERY stable, and I have successfully used single lobe of a deformed TE01 mode to do a reasonably good z-scan of CS2 at 532 nm, at 4 uJ. I have also taken an okay z-scan of CS2 at 1064 nm at 14.3 uJ. I kind of looked funny, perched in a precarious looking position (though it was very stable), when I was alighing the optics to get the laser beam centered on the aperture:


















(Kids, do not align a laser the way you see me doing it here: it is very, very wrong! It is a little too dangerous for the eyes.)

Taking z-scans at lesser energies has been the major hurdle:

• The beam has a lower power, and it needs a certain radius, below which the the beam is so tight, that most of it passes through the aperture during the closed aperture z-scan
• The boxcar is taking very noisy readings, eventhough the laser is very stable -- I ahve noticed a lot of noise on the lines conneting the instruments.

Right now, the system is a little overworked, so I am letting it cool off. I shall hope to have z-scans of samples before my professors walk into the building, in the morning. I am also going to need some coffee. During the last cooling period (when the laser had heated up) I took to some entertainment:




I shall hope to get readings, and analyses, to my professors, this morning.


_____________________________________________

Okay, I was unable to deliver. My prof. says that carving out a portion of the lobe of a TE01 for a gaussian is not the solution, so I have to set up the laser, again, from scratch. Interesting that I was able to get nice looking z-scan curves for CS2, though.