The emergence of high power fiber lasers, and their
applications, is one of the most significant photonics breakthroughs in the
last decade. Fiber lasers consist of a long “fiber-optic active laser medium,”
pumped primarily by diode lasers directed into the fiber cladding.
They have CW outputs exceeding 10KW and can produce
output pulses as short as 10 picoseconds. Because the pump light from the diode
lasers lies in the absorption bands of the fiber laser active medium, the
conversion of input electrical power to output laser power is highly efficient
(30-40% efficiency, as compared to gas and solid lasers with efficiencies below
1%).
Average output powers from fiber lasers can reach as
high as 10KW. Fiber lasers can operate in the CW mode or in various pulse
modes; even picosecond pulses.
Because fiber lasers are smaller, more efficient,
lighter weight, less costly, and their output beams are easier to manipulate
than CO2 or Nd:YAG lasers, they are becoming the laser of choice for
many materials processing applications, such as welding, drilling, cutting and
etching of metals, plastics, ceramics, glass etc.
OP-TEC has developed two instructional modules on fundamentals
and applications of fiber lasers. They can be previewed at http://www.op-tec.org/photonicstechnologies.
We have also identified inexpensive equipment and designed labs to accompany
the modules.
CDs and DVDs are everywhere these days. Whether they are used to hold music, data or computer software, they have become the standard medium for distributing large quantities of information in a reliable package. Compact discs are now easy and cheap to produce. If you have a computer and CD-R drive, you can create your own CDs, including any information you want.
The Disc A CD is a fairly simple piece of plastic, about four one-hundredths (4/100) of an inch (1.2 mm) thick. Most of a CD consists of a piece of clear polycarbonate plastic, shaped like a disc. During manufacture, this plastic is impressed with microscopic bumps arranged as a single, continuous, extremely long spiral track of data. Once the clear piece of polycarbonate is formed, a thin, reflective aluminum layer is sputtered onto the disc, covering the bumps. Then a thin acrylic layer is sprayed over the aluminum to protect it. The label is then printed onto the acrylic. A cross section of a complete CD looks like this:The Spiral A CD has a single spiral track of data, circling from the inside of the disc to the outside. What the picture on the right does not even begin to impress upon you is how incredibly small the data track is -- it is approximately 0.5 microns wide, with 1.6 microns separating one track from the next. (A micron is a millionth of a meter.) And the bumps are even more miniscule...
The Bumps The elongated bumps that make up the track are each 0.5 microns wide, a minimum of 0.83 microns long and 125 nanometers high. (A nanometer is a billionth of a meter.) Looking through the polycarbonate layer at the bumps, they look something like this:The bumps are arranged in a spiral path, starting at the center of the disc. The CD player spins the disc while the laser assembly moves outward from the center of the CD.
CD Player Components The CD player has the job of finding and reading the data stored as bumps on the CD. Considering how small the bumps are, the CD player is an exceptionally precise piece of equipment. The drive consists of three fundamental components:
A drive motor spins the disc.
A laser and a lens system focus in on and read the bumps.
A tracking mechanism moves the laser assembly so that the laser's beam can follow the spiral track.
You will often read about "pits" on a CD instead of bumps. They appear as pits on the aluminum side, but on the side the laser reads from, they are bumps. The incredibly small dimensions of the bumps make the spiral track on a CD extremely long. If you could lift the data track off a CD and stretch it out into a straight line, it would be 0.5 microns wide and almost 3.5 miles (5 km) long! To read something this small you need an incredibly precise disc-reading mechanism. The key element in this mechanism is the pinpoint beam of a laser.
The fundamental job of the CD player is to focus the laser on the track of bumps. The laser beam passes through the polycarbonate layer, reflects off the aluminum layer and hits an opto-electronic device that detects changes in light. The bumps reflect light differently than the "lands" (the rest of the aluminum layer), and the opto-electronic sensor detects that change in reflectivity. The electronics in the drive interpret the changes in reflectivity in order to read the bits that make up the bytes.
The hardest part is keeping the laser beam centered on the data track. This centering is the job of the tracking system. The tracking system, as it plays the CD, has to continually move the laser outward. As the laser moves outward from the center of the disc, the bumps move past the laser faster. Therefore, as the laser moves outward, the spindle motor must slow the speed of the CD. That way, the bumps travel past the laser at a constant speed, and the data comes off the disc at a constant rate.
CDs store music and other files in digital form -- that is, the information on the disc is represented by a series of 1s and 0s. In conventional CDs, these 1s and 0s are represented by millions of tiny bumps and flat areas on the disc's reflective surface.
To read this information, the CD player passes a laser beam over the track. When the laser passes over a flat area in the track, the beam is reflected directly to an optical sensor on the laser assembly. The CD player interprets this as a 1. When the beam passes over a bump, the light is bounced away from the optical sensor. The CD player recognizes this as a 0.
The advent of CD burners marked a huge cultural shift. The technology made it feasible for the average person to gather songs and make their own CDs. Today, writable CD drives (CD burners) are standard equipment in new PCs, and more and more audio enthusiasts are adding separate CD burners to their stereo systems.
CD burners darken microscopic areas of CD-R discs to record a digital pattern of reflective and non-reflective areas that can be read by a standard CD player. Since the data must be accurately encoded on such a small scale, the burning system must be extremely precise. In addition to the standard read laser, a CD burner has a write laser. The write laser is more powerful than the read laser, so it interacts with the disc differently: It alters the surface instead of just bouncing light off it. Read lasers are not intense enough to darken the dye material, so simply playing a CD-R in a CD drive will not destroy any encoded information.
When I was a young boy, I thought the only places where batteries were needed were in flashlights. Then I learned that we had one in our car to get it started. As a young adult, I knew we needed lots of batteries to operate our children’s toys. Now we need them for laptops. Batteries continuously get more important in my life; now they’re vital to the future of alternative energy—particularly wind energy and solar voltaics. Actually, I think they’re absolutely critical to the practical use of these two forms of “green energy”.
Solar voltaic cells and windmills convert these two forms of free, available, natural energy directly to electricity—and only at the times when they are available (i.e., when the sun is shining or the wind is blowing.) So, the problem is that we have to use their electric energy at the precise time when it is available, or we have to be able to store it until it is needed. We will probably need to store the energy from solar voltaics for at least 6-8 hours; that’s a pretty large supply to store.
I can easily think of two possible ways to store this energy:
1.Hydraulically—Use the electricity to pump water up to the front of a dam, and release it, when it is needed, through turbines to drive electric generators (i.e., hydroelectric power.) The problem with this approach is that there aren’t enough dams available to make this approach more than a “drop in the bucket.”
2.Chemically—This is where we need to go. Use the electricity to “charge large batteries” and discharge them when we need it.
From an energy perspective, we are developing batteries for two purposes. To power hybrid-electric, or all-electric cars and to store alternative energy supplies. We’re not ready for either of these applications yet, but we’re working on it. When we are ready, will we need technicians? And where will they come from?
In the March 2, 2009 edition of Newsweek, there is an article on the future of batteries, entitled “To Pack a Real Punch”, which is an interview with Alex Molinaroli, the president of Power Solutions at Johnson Control. Molinaroli says that batteries are the key to our energy future, “You have to match energy production with the demand. That’s easy to do when you have oil or coal in the ground that you can pile up, but you can’t do that with electricity. You have to be able to store it somehow”. Molinaroli is confident that appropriate battery technology can be developed quickly, now that the demand is evident.
If we can practically develop very large battery systems, then we can use “solar parks”; if not, we’ll have to generate and store solar energy “one building at a time”.
Today, the leading technology in battery development is in lithium-ion batteries; the technology is concentrated in Korea and Japan, and some in China. This development has been driven by the needs in electric car development. Other materials for batteries are also being investigated to reduce cost, charging/recharging time and weight/volume. New breakthroughs in battery technology are likely, and they could emerge in the U.S.
The urgency for U.S. battery technology development has emerged rapidly in recent months. We can still be first in this race (and we need to be). But if we want to keep the products from this new technology in the U.S. we will have to prepare for this race—and part of this preparation is to have the appropriate technical workforce to support it.
What areas of technical education are best suited for preparing the workforce in battery development and production? What are the knowledge and skills required for cutting-edge workers in this field? A few weeks ago, I wrote a few blogs about the potential for optics and electro-optics in solar voltaic development, production and use. Battery storage of solar energy will also be critical.
As technical educators we need to think “outside the box” as we anticipate the knowledge and skills for techs in emerging fields such as solar voltaics. From OP-TEC’s view, we are interested in solar voltaics because of the skills required in optics and electro-optics. But Solar Voltaic Techs (if there are to be such workers) will probably need a combination of knowledge/skills that include optics & electro-optics; but also may include technologies related to new batteries—and possibly other technologies.
Labels: batteries, renewable energy, green energy, solar energy, solar voltaics, optics, photonics, technicians
OP-TEC, the National Center for Optics and Photonics Education, is funded by the National Science Foundation's Advanced Technological Education (ATE) program. We are working with secondary, postsecondary and industry partners to increase and sustain our nation’s capacity to produce photonics technicians.
OP-TEC is funded by the National Science Foundation's Advanced Technological Education (ATE) program. We are working with secondary, postsecondary and industry partners to increase and sustain our nation’s capacity to produce photonics technicians.
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