Amy's Science Blog
May 16, 2012 My First Technical Conference
From May 6th to 9th, I attended my first technical conference, which was an optics conference called CLEO (Conference on Lasers and Electro-Optics) in downtown San Jose. I felt very out-of-place being both a girl and an undergraduate, both rarities in the technical conference world. On Sunday afternoon, I stopped by the conference to check in. The check-in lady handed me a name badge with a green ribbon hanging off of it announcing PRESENTER. Then she gave me a plastic bag covered in Maxwell's equations. Inside was a spiral bound book as thick as a textbook full of the abstracts for the hundreds of presentations occuring over the course of the week. Besides the giant booklet there were a bunch of flyers announcing free gifts and i-pad drawings from optics companies displaying their goods at the exhibition. Next I went to the special presenters' room to look at my slides as they would appear on the big screen. After making some last minute changes, I wondered around the conference center. The presentations did not start until the next day, so I timidly sat down at the only table in the foyer with any people at it. The young men greeted me warmly. It turns out they were all from the University of Auckland. They asked about my research, and told me not to be nervous about my presentation the next day.
That night at the hotel, I practiced the first two minutes of my presentation over and over again for the post doctorial fellow from my lab. He told me the start was the hardest part of a presentation. Then we went to dinner at Denny's where we happened upon my research advisor from the University of Minnesota from the summer after freshman year. The optics world is a small world.
I fidgeted in my seat as I waited for my presentation turn. I was so nervous that I thought I was going to throw up. I was the fifth presentation out of eight 15 minute presentations in the section on Remote Optical Sensing. The man before me was a big-shot in the world of remote optics, so when he ran over time, the session presider did not have the courage to cut him off. The man kept talking faster and faster for the last five minutes of his presentation until he was talking so fast that no one could understand him. As I stood up before the group, I noticed the room had overflowed for my presentation. Everyone must have seen the press releases about our group's exciting new research that could "take pictures around corners." The presentation went by in a blur. At the end, I checked my clock, and it had only taken eight minutes, when it was supposed to take twelve. Luckily, this solved the presider's problem that our section was behind due to the previous presenter. I received four questions, and the post doctorial fellow from my group gave me a big thumbs up when I answered the questions well.
I was done. Now it was time to enjoy the conference.
There were three types of technical talks. There are the traditional 15 minute presentations, which were the majority of presentations. Then there were invited talks, which exhibited research that the reviewers found promising, so the speaker was given 30 minutes. Finally, there were tutorials, where the speaker was a well-known researcher in the field, and they were asked to give a one hour overview of a field.
Within the optical remote sensing section where I presented, I discovered the hot new topic is the "sky laser." The goal of the sky laser is to send a laser signal into a cloud (or other atmospheric feature to to be studied), which then interacts with the atomosphere and causes it to lase. Thus, the returning signal is a tight, directional, coherent band, which is easier to detect than the faint, diffuse, scattered, and incoherent signal that returns using tradition remote sensing methods.
Another cool field I learned about was laser filaments. Due to nonlinear optical effects, one can create a self-focusing laser beam. If the beam is intense enough, it creates a plasma in the atmosphere, called a filament. This filament guids the laser light like a waveguide and causes the light to propogate without diffraction. The postdoctoreal fellow from my group did his PhD work with a professor at the University of New Mexico, who is a leader in the area of filaments. His tutorial interested me for nonlinear optics, and I hope it is one of the first classes I can take at Stanford when I start my PhD next year. His research students were also very kind and took me under their wing during the week, taking me out to dinner and inviting me to attend presenations with them.
My favorite tutorial was presented by a professor at Rice University that had graduated from MIT back in the day. He gave a talk on terahertz technologies that really started from the fundamentals, so that someone with only a basic college physic class in electromagnetics could follow. He described the difficulties of manipulating terahertz waves, because neither the traditional signal processing and antenna methods of radio waves or the optical methods of visible light worked at this frequency. This inbetween frequency required design of new waveguides and sources to produce the waves. The professor was an engaged and peppy speaker that woke me up after listening to hours of other presentations.
Starting on Tuesday, the exhibition hall was open. Optics companies from all over the world came to show off their wares and attract business. They also gave out a lot of free things. I got a free backpack from Newport, a free t-shirt from Thor Labs, a mug from Femto Lasers, a canvas grocery bag from Edmund Optics, a flashlight and "Girls in Optics" planner from SPIE (International Society for Optics and Photonics), a free copy of Nature Photonics, and a plethora of pens from various companies.
Tuesday evening the Optical Society of America (OSA) sponsored a student happy hour at a local bar. I met six grad students from Canada (University of Toronto). Of the roughly 50 people there, only three were girls. After an intense day of presentations, it was nice to relax and discuss something besides optics.
All in all, my first technical conference was an exciting success. I met a variety of researchers in the optics field. I ran into several profesors I was interested in working for at Stanford, and I ran into an old friend who was a graduate student when I worked at the University of Minnesota. Each day I spent roughly eight hours attending technical presentations and learning about a variety of optics fields. I started to find my place within the optics field, both through a variety of presentations and through interactions with researchers. I look forward to my next conference.
April 9, 2012 Making the Largest Mirrors in the World
One of the universities I applied to for graduate school was the University of Arizona, which has one of the premiere optics research centers in the United States. As part of their research facilities, the School of Optical Sciences has a state-of-the-art mirror production facilty. Located under the seating for the Arizona Stadium, the Steward Observatory Mirror Lab produces the largest mirrors in the world for use in telescopes. I had the opportunity to take a tour of this lab while I was visiting the university.
The largest mirrors they have made so far is 8.4 meter diameter mirrors for the new Giant Magellan Telescope. In the end, the Giant Magellan Telescope will be composed of 7 different 8.4 meter diameter mirrors pieced together to make one giant 24.5 meter diameter detecting mirror for the telescope.
Computer generated model of the Giant Magellan Telescope, which is currently
under construction. Image from Steward Observatory Mirror Lab website.
Construction of a single giant mirror can take over six months. The secret to creating these large mirrors is making them hollow. The first step is to build a giant honeycomb mold. Glass is melted in a furnace and oozes into the the cracks between the honeycomb supports. Over a several month period the glass is slowly allowed to cool. The entire mold and furnace sits on a spinnable floor. As the glass cools the mold is spun. The centrifugal force of spinning causes the glass to form a parabolic shape, which is the desired shape for a telescope mirror. Therefore, the spinning oven process greatly reduces the amount of grinding needed to complete the mirror.
The rotating mirror oven. Image from Steward Observatory Mirror Lab website.
Next the mirror is placed vertically and the honeycomb mold pieces are broken out of the mirror. Metal supports are attached to the back of the mirror. The mirror is then placed face up beneath a giant diamond grinding machine, which grinds the surface of the mirror down to its precise curvature. Afterwards, polishers are used to smooth the ground surface and remove any nanometer-sized discrepancies in curvature.
Left: Metal supports have been added to the mirror. Right: Polishing of mirror. Images from Steward Observatory Mirror Lab website.
A giant tower in the Steward Observatory Mirror Lab allows for the testing of these giant mirrors. A laser is housed at the top of the tower and used to do interferometry on the surface of the mirror. This allows the determination of the shape of the mirror to within nanometers, so the engineers can find any imprecisions in the mirror.
Finally, the mirror is shipped to an observatory where it will be put in a telescope. The final mirror coating will be added to the glass at the site. Every few years the observatory will have to recoat the glass substrate with this mirror coating.
For more information about how the world's largest mirrors are made, you can visit the Steward Observatory Mirror Lab website.
March 17, 2012 230% Efficient LED
Last week my friend chatted me on Facebook and asked, "People at your school have apparently built a 230% efficient LED. Do you know how this works? Seems like it would decrease entropy." My initial response was, "How can you have over 100%?"
I read the popular science blogs and their description of the experiments (see Wired or Gizmodo), but I found their description lacking. They explained that the LED converted lattice vibrations (a form of heat) to light to increase its input electrical power to output efficiency above 100%, but they did not explain how this mechanism worked or what the limitations of converting heat to light were.
Then my friend asked, if we lined up a bunch of these LEDs on top of a Google computer server farm, could we use the heat produced to light a bunch of LEDs and also cool the computers? He saw this as a decrease in entropy, or in other words violation of the second law of thermodynamics. The second law of thermodynamics says that overall entropy must always increase in the universe. Entropy is a measure of disorder in the world. In other words, the disorder in the universe must always increase, and heat is a form of disordered energy. First of all, I want to point out that turning heat into work again is not a violation of the second law of thermodynamics. For example, a steam engine works by converting heat into work. The key to the second law of thermodynamics is that all the heat cannot be converted back to usable energy. Some of the energy is lost for good. Heat is commonly turned into electromagnetic radiation (which includes the visible wavelengths called light). The sun and the earth are both black bodies, which are at a stable equilibrium temperature from taking in energy, which heats it, and radiating electromagetic waves as a result of this heat, which cools it. Laser cooling systems, used to cool down atoms to near absolute zero temperatures are another example of turning heat into light. The trapped atoms give off energy in the form of photons (the particle name for light) as they cool.
To learn more about the research on the efficient LEDs, I turned to the original article in Physical Review Letters (avaliable to those with subscriptions here). It turns out that scientists have known for decades that we can theoretically create a light source that outputs more energy than electrical energy input by converting heat into light. M. A. Weinstein actually wrote a paper in 1959 analyzing the input and output of entropy from a theoretical light source to calculate thermodynamic limitations on the conversion efficency of such a light source (again, if you have a subscription, you can view the article here). Weinstein found that for a room temperature light source of practical brightness, the maximum efficiency would be 160%, limited by the second law of thermodynamics. Weinstein also points out a key difference between heat, work, and light when thinking about the second law of thermodynamics. He describes heat as completely disordered energy, work as completely ordered energy, and light as partially ordered energy.
Wait, so how did the scientists at MIT get 230% efficiency then?
The important facts that Wired and Gizmodo left out is that the MIT scientists tested this LED under abnormal conditions. The ambient temperature was 135 degrees Celsius, which is over boiling, and the light radiated was only 69 picowatts (10-12 watts) of light, where the average light bulb has a brightness of about 60 watts. This limiting case is not necessarily practical for every day applications.
Now, this video below is completely off topic, but I thought it would be a fun video to share. I found it while reading about Higgs bosons in the internet for class. Higgs bosons are a theoretical particle that scientists hope to prove the existance of at the Large Hadron Collider (LHC). The video has a new age flavor to it, but it explains concepts at a good level for all to understand. Enjoy!
March 3, 2012 The Navy's Railgun
While finding a news article for German class in Der Spiegel, I ran upon this video clip released by the US Navy depicting the new protype for their railgun. Their goal is to create a railgun that can shoot 40 pound projectiles at 7 times the speed of sound (2.8km/s) up to a distance of 160 km. The US Navy has spent $240 million dollars since 2005 on railgun research, and it hopes to have railguns on their ships starting in 2017.
In the video, flames pour out of the railgun as the projectile exits. According to the director of testing, Tom Boucher, the flames are caused by melting metal fragments and electricity arcing across the rails. You also can see a mirage in the wake of the bullet. The mirage is caused by a change in the refractive index of air due to the heat of the projectile.
So, how does the railgun work?
A railgun is the application of basic electromagnetic physics. Current is sent down two parallel conductors (called rails) in opposite directions, creating a magnetic field around each conductor. If a conducting projectile is placed between the two rails, then current will flow from one rail to the other through the projectile. Current is the movement of electrons through the metal conductor. The magnetic field interacts with the electrons flowing through the projectile and causes a force on the projectile, propelling it. This phenomenon is also what drives electric motors, and it can be summarized as the Lorentz force law, F=q(E+vxB). E is the electric field (which is not involved in this problem), B is the magnetic field,q is the charge (of the electron in this case), and x is the cross product (an operation to find a vector orthogonal to two other vectors).
image from Wikipedia
Advantages and Disadvantages of the Technology
The advantage of the railgun is that it uses only electricity, and not gunpowder, to launch projectiles. It can theoretically launch projectiles faster, farther, and with more accuracy than traditional explosive weapons. The disadvantage is currently the wear and tear on the projectile and rails. The extreme forces and heat caused by launching degrade and deform the barrel after several launches. Furthermore, if the Navy would like to insert a navigation system into the projectile, engineers will need to find a way to protect the electronics from the heat produced. Finally, the amount of electricity needed to launch the projectiles is greater than current power capabilities of navy ships. Scientists will have to work on capacitor and battery technologies, and engineers will have to design a battery system to supply the railgun with its high current needs.