I was also in a meeting! I went with the two grad school students I work with, Cory and Brittany, and in the meeting they discussed upcoming demos, materials they needed, a lot of other stuff that I didn't understand, and then they mentioned a video card, like for your computer. Man, did my ears perk up at that! The lab bought a new and quite good video card for a computer in one of the labs, and I remembered that when I visited the lab a few days earlier, the computer wasn't very high-spec at all, so I mentioned that the computer might not be able to power the card, but they just said,"Oh, it'll be okay." Of course, I was like "um, are you sure?" In my head, of course. It would of been rude if I blurted that out.
To be honest, I'm surprised to be incorporated so quickly. Press, demo, meeting all in one week. That's a lot, and all on different days too!
Also, I ride Cat Tran from the parking garage to the College of Optical Sciences, and I must say that I find it incredibly convenient, though there is this one street that is I think the most uneven street in the world! The bus just bounces like crazy on this street, the windows are super rattle-y, and I swear I spend more time in the air than in the seat during this part.
Also, next to my lab room is another room that is having a change in people, so the old people moved somewhere else, but before the new people come in, the room was, um, "nice-ed up." I wouldn't hove thought much of it, if the "nice-ening up" process didn't involve BANGING ON THE WALL FOR HOURS ON END. It gets really annoying around the third hour or so.
Now, on to the technical stuff (in other words, you can skip to the pictures if you want. You know who you are). From my last post, you know that I created an interferometer, and saw how there was interference on the wall. However, there is this property of lasers called coherence length, which essentially means that if I were to take either the east or south mirror (see last post), and move it away from the beam-splitter, there would be a point where you would lose interference, and that distance would be the coherence length. So, after I made my interferometer, my next task was to use it to find the coherence length of the Helium-Neon (HeNe) laser (which is the red laser in my last post). "Okay, this can't be that hard, right?" WRONG! So I was able to manipulate my setup so that the length was 6 meters, and it still had coherence! What the heck? Also, another property of lasers is divergence, which essentially means that the laser beam gets bigger over some distance, but the intensity (think brightness) is also weaker. At 6 meters, the beam was huge, but also really faint! Okay, let me correct myself. Technically, the beam is still small. The reason the beams were so big in my last post was because the beams are sent through a lens at the end, which magnifies the beams. However, that also means that it amplifies any kind of increase in beam radius, in this case divergence. For instance, normally, the beam is, say, 1 mm in diameter on the wall. When the laser goes through the lens, the diameter becomes about 300 mm. A 300 times increase in size. At 6 meters, the laser diverges and the beam radius is now 2 mm. Send that through the lens and it's now 600 mm! But remember that brightness decreases with bigger beam radius, so it's also a lot fainter. Ok, so back to the setup. At 6 meters, I couldn't extend the distance anymore, the beam was really faint, and it still showed interference. I asked Dr. Blanche what it should be, and he didn't know (which is why I was doing this in the first place. He was "curious."), so we looked up the approximate coherence length of HeNe lasers, and guess what it was? IT WAS 100 METERS! I can't do 100 meters! I'm running out of space at 6! And the beam was really faint! Yeah, so we just said that the coherence length of the HeNe laser was greater than 6 meters and left it at that.
The lab also got a new laser, a green one, a Nd:YAG (neodymium-doped yttrium aluminium garnet) one. Yeah, we just call it the "YAG" laser. Since it's a new one, we have no idea what the characteristics of the laser are. So, next task: characterize the laser. Step one: make interferometer for the YAG laser, then find coherence length. Note about green lasers: your eye is most sensitive to green, which is why green laser pointers seem "brighter" than red ones at the same power output. Also, this laser is a Class 4 laser, which means that is was a eye, skin, and fire hazard! Dangerous stuff! So how can I safely use this laser? One option is to use eyewear. However, the problem with this is that I can barely see the laser with the eyewear on (or not at all, see pictures), which means that I might accidentally cross the beam, so that was no good.
Eyewear: Glasses and Goggles
Green Laser With No Eyewear
Dot Nice and Bright
Green Laser Through Glasses
Can sort of see the dot
Green Laser Through Goggles
Can't see the dot
The other option is to weaken the beam. How do you do that, you ask? What you do is that right outside where the laser comes out put a Neutral Density (ND) filter, which essentially reflects back most of the laser, and letting the rest of the laser through, in my case 90% was reflected, 10% went through. This was, I could safely see the beam, and making it easier to set up the interferometer.
ND Filter
You can see the beam! The lower line is the reflected beam, 90% of the upper line
Also, I would like to mention alignment. It's very important in optics that everything is level. That, however, is probably the biggest pain in the butt to do. There's a lot of tweaking that was needed to be done just to make the thing level, and it took FOREVER. Like, you fix one piece, but that messes up another piece, and when you fix that piece, you mess up the first piece, and when you fix that one, the second one is messed up again, etc. There's a lot of back and forth in alignment. Also, interference is different. Typically, when you think of interference, you think lines. That may be the case in the double slit experiment, because the slits make the lines, but when dealing with beams, the inference should look like concentric circles (see pictures). If you see lines, that means that your setup is not aligned properly (so technically the pictures in my last post show that my setup wasn't aligned right, but I didn't know that!).
Not Aligned: Lines
Anyways, this time around, I was able to get up to 22 meters for the coherence length (I had more space, and I learned a trick where you can bounce the laser beam in between two mirrors multiple times) before running out of space, but the beams still showed interference, and divergence was still a problem. Estimated coherence length: 30 meters. So at least I got closer! So we (again) just said that the YAG laser had a coherence length greater than 22 meters and left it at that.
Next, I was to determine what the wavelengths were of the lasers in the lab. Of course, I was like, "You don't know?!?" (in my head. They seriously didn't, though). So, I borrowed a spectrometer for another person and set it up, which was a challenge all on its own! So I get this spectrometer, and it turns out that it needs software in order to record whatever the spectrometer is reading. Simple enough, right? NOPE. So I look on the manufacturer's website, and they have this software for download. I download the install program, run it, and lo and behold, it requires a password to install! Online searching gave no avail, so I go back and ask the guy I borrowed this from if he knew. He searched a few places, didn't find it, but he said he knew a guy who did, so we went to go find that guy, and that guy found it (FINALLY) on a post-it note on a CD for the software. I thought just needed the password, so I took that and type in the password into the install program and it all worked well. NOT. It didn't recognize the password! So then I thought that maybe the password was specific to the CD, so I get that, run the CD, and I finally installed the program. However, for some reason it couldn't recognize the spectrometer, so I had to go look for a driver for the spectrometer. I look back at the manufacturer's site, and find this driver, but to install it, it required ANOTHER password. So I ditch that, and then I remembered that on the CD it had another part to install drivers. I run that, and yet ANOTHER password gets in my way. And yes, I tried the password that worked for installing the software, and it didn't work. You can probably tell that by this time, I was SICK of passwords. Then this window pops up: "Windows has detected new software. Would you like to find drivers for this?" or something similar, and I was like, "What the heck. Might as well give it a shot," not expecting much. Next thing you know, it finds a driver, installs it, and voila, it worked! It freaking worked! Of course, I thought, "Windows is amazing!" followed by "How did it find it?" followed by "How come I couldn't find it?!" My ego took a little hit there. Anyways, the software wasn't exactly user-friendly, just finding out how to save the information was a pain. Let's just say that I learned a lot about user manuals. I took measurements of the lasers, analyzed them, made graphs with Excel, you know, Science 101: Scientific Method.
Spectrometer
My Best Friend Setting Up the Spectrometers:
Scotch Tape! To Hold the Accursed Device in Place
One of the Lasers I Analyzed
Also the Strongest and Brightest Laser in the Lab!
A Closer Look at the Laser
You can FREAKING SEE THE LASER, and it's so bright, it makes glass glow white!
Lastly, right before the weekend, Cory gives me this reading material for over the weekend, and there are some integrals on the page, and during his quick run-through of the material, so I know what to expect, he says this: "I can't imagine that you took calculus, so you can ignore this [points to the integrals]." Of course, I had to be nice and politely say that I did indeed know calculus, but MAN. It took all my willpower not to say something sarcastic or pompous that starts with something like "Well, let me tell YOU something..." or "[cough cough] EXCUSE me? Did you just say what I THINK you said?" I can't blame him, because he doesn't really know me yet, but that was probably the closest time I had to losing my professional composure. I know I "represent BASIS" and all that, but SERIOUSLY.
So that was my week. Challenge at times, but also a lot of fun! Can't wait for next week!
As a bonus for reaching the end of this really long blog post, one of the original holograms ever made!
The Hologram
To think that of all things, they picked dinosaurs...
I diffused the laser to see the hologram, but a red LED would work too,
along with a green laser similarly diffused or a green LED
1 comment:
Imagining a Joseph who doesn't retort to being accused of not knowing calculus is quite the endeavor! Your work seems quite impressive Joey.
Post a Comment