Undergraduates and the Future of Optics

The past week or so has been busier and more exhausting than usual (with a little girl who is suddenly having trouble getting to sleep), so I missed the blog last week. My daughter’s ability to sit up and stand easily is causing her all sorts of trouble. Whenever we lay her down in her crib, she thinks she should immediately stand up and walk around her crib (still holding onto the side). She is, of course, exhausted and needs a nap but can not quite figure out that she needs to lie back down in order to sleep. Poor kid (and poor parents!).

Having found some time to myself again after a few long weeks, I decided to do some more exploring on the Frontiers in Optics website. While the full conference program will not be up for some time, there are tons of exciting invited speakers and special symposia listed for the conference. I am going to have a hard time deciding what things to go to with so much going on – one of the big challenges of the big conferences with so many concurrent sessions.

Two of the special symposia struck me as being really interesting and related: The Future of Optics: A Perspective at Emil Wolf’s 90th Birthday and the Laser Science Symposium on Undergraduate Research.

The Future of Optics Symposium is going to address the future of optics in the areas where Emil Wolf contributed the most – Inverse Problems, Coherence and Quantum Optics, Physical Optics, and Optics at the University of Rochester.

I am especially interested to hear Anthony Devaney’s talk about the Future of Inverse Problems since this relates directly to my own research in Optical Diffraction Tomography. While there are a lot of exciting areas of research dealing with new technologies in lasers, fabrication, and nanotechnology, I am always fascinated by how much there is left to learn and investigate in the very fundamental problems of optical scattering and propagation. Being able to measure the intensity profile of light after it has passed through an object and then reconstruct that object allows us to image objects that standard microscopes cannot see. And, of course, as we learn to make smaller and more complicated structures, we need ways to measure them.

This symposium seems like a wonderful way to honor a great scientist and get the younger generation excited about the exciting research that is coming up in these fields. And, speaking of the younger generation, there is another special symposium just for them: The Symposium on Undergraduate Research.

I only found out about this symposium a couple of years ago, though it has been going on for 12 years now. This is an opportunity for undergraduates to come and be involved in a large and vibrant conference. If you are an undergraduate (or have undergraduates in your lab), you should definitely look into this.

The organizer is Hal Metcalf from Stony Brook University and the deadlines for submission are at the end of the summer (instead of May) to accommodate undergraduates who usually do the bulk of their research in the summer. The symposium consists of oral presentations and post talks and the quality is really amazing – many of these presentations could easily have been given in the main conference sessions and no one would have thought they were undergraduates.

I had three students who worked with me present at this symposium in 2010 and they could not stop raving about what a wonderful experience it was. Two of my students had not planned on pursuing optics after graduation, but were so excited by the experience that one is now a graduate student in optics and the other is planning on applying for optics programs this fall.

I feel like a walking advertisement for this symposium, but I just think it is such a fantastic opportunity for undergraduates to be introduced to the vibrant optics research community. Especially for students in smaller departments who do not normally have access to these sorts of opportunities. And, of course, it is a great place for graduate advisors to recruit really phenomenal future graduate students.

Being very education and student-oriented, I think it is really cool that in addition to talking about all the current (and exciting!) research, part of Frontiers in Optics is devoted to looking toward the future of research – both in specific topics and in supporting and engaging the future scientists who will be the ones to engage in these topics.

Crawling and electrical outlets

My daughter has just started moving. We are fortunate that she started moving later than some other babies we know.  We have had a blissful 10 months of not having to chase after her and put up gates in the house. Alas, that is all over now.

She is not crawling exactly, but she scoots forward. She reaches forward onto her hands while sitting and uses one leg to pull herself forward and drags the other leg behind. I have seen many of her cousins doing something similar, at pretty high speeds. This may turn into a standard crawl someday soon, or maybe not. Either way, she is definitely moving around, and faster every day.

Last week, I put her down on the floor in the bedroom so I could pick up some clothes to do some laundry. She usually goes straight to playing with our window shades, which is relatively safe. That day, though, I turned my back for just a second and she went straight across the room to the electrical outlet. Yikes! I had not yet put the safety plugs in upstairs. It is crazy how she always goes straight for the electrical outlets. They are right at eye level and are apparently quite fascinating.

So why are electrical outlets so dangerous for little ones?

First of all, can she even get her little fingers in those tiny little holes? In order for an electrical connection to be made, she needs to touch the metal connections. Even with her very little fingers, I do not think she could get them into the outlets. That being said, I certainly do not want to let her try!

I think the real danger is probably having her put one of her toys into the outlet and making an electrical connection that way. Many of her toys are plastic or rubber right now, which do not conduct electricity effectively, but she does love to play with metal things. Also, she gets into everything now that she is mobile and I let her play with anything that does not seem dangerous, so it is not unlikely that she would find something to put into that outlet.

What happens if she does manage to get something into the electrical outlet (finger, fork, etc.)? The outlet has 120 V of potential – that means that it has energy that is ready to start flowing. If you ‘complete the electrical circuit’, i.e. give that energy somewhere to flow, it will start flowing – through you.

So how much current will flow through your body if you touch an electrical outlet and what is a dangerous level? Ohm’s Law tells us that voltage, V, (that 120 V for a standard household outlet) is related to current, I, and resistance, R, through the following equation:

The amount of current that flows through us depends on our resistance to that current.

So what is our resistance? That turns out to be a complicated question because it depends on things like how dry (or wet) our hands are, and how much contact we make with the metal wires. If we connect with the wires over a large area of our bodies, our resistance is lower – it is easier for current to flow through us.

Dry skin has a larger resistance than wet skin. This is fortunate for me as a teacher. I accidently shocked myself with a 500 V source in the lab once, but my hands were covered in chalk and the contact between my hands and the wire was small. It was definitely not a pleasant shock, and I felt dizzy for a little while after, but there was no serious or permanent damage. On the other hand, I have also shocked myself on a 120 V outlet in a lab (no chalk) and it was quite painful. Who knew the life of a physicist could be so dangerous?

But I have not answered the question. What is our resistance? I had my students measure their resistance in a teaching lab using very small metal probes (small area of contact). They measured from one hand to the other and found that they had a resistance of about a megaohm – that’s one million ohms. However, an article on Electric Shock on Wikipedia cites the International Electrotechnical Commission as showing adult resistances at 100 V of ~2000 ohms. They use larger contact areas, but you never know when you shock yourself how much contact you will have, so it is much safer to assume your resistance will be low.

Okay, let us assume, to be safe, that our resistance is about 2000 ohms and the voltage of the outlet is 120 V. From the equation above (Ohm’s Law), we can calculate that this situation would send 60 milliamps (mA) of current through us. That does not sound like a lot, right? Well, an amp is a LOT of current. The same Wikipedia article cited above states that humans can feel 1 mA of current. Currents as low as 60 mA (and sometimes lower) can cause fibrillation of the heart muscles, which can lead your heart to stop.

Depending on the voltages and contact situation, electrical shocks can also cause serious burns. I had minor burns on both hands when I was shocked by the 500 V lab source. (I should note that I am always very careful around electrical sources and in both cases of being shocked, I was working with wires that had been previously damaged  – a good example of why you should always have broken or old wiring repaired immediately.)

Okay, I am convinced. I should cover up my outlets and keep my daughter safe! So far we have just put in some standard outlet covers, though I have read in several places online that these covers are too easy for toddlers to remove. Fortunately, my daughter is too young to have figured that out yet (and trust me, she has tried!). As she gets older, and stronger, and more coordinated, and smarter, we may have to come up with better ways to keep her safe.

We are definitely entering a new stage of parenting. It is amazing to watch her learn to move and explore her world and I am very much enjoying it, but with every new development comes new challenges.

Infant Vision Research

I am planning on attending Frontiers In Optics this October. Although I am taking some time off from research and teaching to be with daughter, I would like to keep up with current research for when I go back to work in optics. This conference seems like a perfect opportunity to do so.

The conference is not for several more months, but they have already started posting information about speakers and special events online. One of the things I think is great about a big conference like this is that I get a chance to learn about a number of interesting topics that are not related to my own research (as well as many that are).

I was looking through the conference program and saw that there is a special symposium on Understanding the Developing and Aging Visual Systems. My own research is very different and I do not know that much about the eye, but I noticed that there are a couple of talks on infant eyes and vision. Ever since my daughter was born, I have been interested in the physics (and optics) of babies, so I immediately looked up some of the speakers.

Richard Aslin, from the University of Rochester, and Rowan Candy from Indian University both had the word infant in the titles of their talks, so I checked out their research web pages. I found out a lot about infant vision and some really fun links.

A few months ago, I wrote about what I can see in my daughter’s eyes. This Tiny Eyes website helps me to better understand what my daughter is seeing with those beautiful, inquisitive eyes. This site is so much fun – anyone with any interest in babies should go there to play. It let me upload a picture of one of my daughter’s toys (I chose her truncated icosahedron of course) and then showed me what this toy would probably look like to my daughter at different ages and different distances from her eye.

To give you an idea of how her vision develops over time, I looked at images of this toy held two feet away from her eyes, at different ages:

You can see how her vision progresses from seeing just a fuzzy blob when she is first born (upper left) to starting to see details around 8 weeks (upper right) to being able to see the toy more like I see it now that she is 10 months old. My daughter became much more interactive and interested in her toys (and less fussy) around 3 months. Maybe this is because she was starting to really see things? Now she likes to roll (bounce, throw, etc.) the ball back and forth.

The research on infant vision is really amazing. Rowan Candy’s group looks at eye movements and the electrical activity in the brain in infants to study the difference between normal and abnormal eye development. Eye tracking and brain imaging using near infrared light help Richard Aslin’s group learn how infants use visual cues in their learning and development.

For those of you less interested in infants, there are many other talks on the imaging and research into eyes and vision (including a plenary talk by Richard Williams on “Imaging Single Cells in the Living Retina”). I have plenty of eye issues myself, being pretty severely near sighted and having two eyes that do not work together, so I find this area of research really fascinating for personal reasons as well as being amazed at the cool optics involved. Sadly, my daughter will likely inherit my (and her father’s) terrible eyes.

Eyes and vision are certainly not my main area of research, and likely never will be, but my main focus has always been teaching and my students love to hear about how optics is related to the human eye. These types of topics get them really excited and motivate them to want to learn more.

Note to Laser Mom readers: I will be posting about Frontiers in Optics from time to time until the conference in October in lieu of my usual articles. Hopefully you will find these topics as interesting as my usual Physics thoughts and will enjoy learning more about the new and exciting things going on in the world of optics.

Seasons (or Why My Front Door is Hotter in Winter than Summer)

We moved to CO a few months ago and when we first moved into our new place, I noticed that our front door, which is south facing, became very hot on sunny days. This was March and so I was worried what it was going to be like in summer. Even in March, I was afraid my daughter was going to hurt her hands is she touched it. Interestingly, now it is June, and it is regularly 90 deg and sunny, but the front door stays cool to the touch. This got me thinking about the sun and seasons…

If you have not taken an Astronomy course, you may not spend a lot of time thinking about the solar system and how the Earth moves in relation to the Sun. You may also not have thought much about what causes summer and winter and why the days are longer in the summer.

This week is the summer solstice for the northern hemisphere. The solstice this year is June 20. So what is the solstice, what does it mean about the Earth and the Sun and why do we have seasons? Why does the Southern Hemisphere have opposite seasons?

A common misconception is that summer occurs when the Earth is closest to the Sun and winter occurs when the Earth is farthest from the Sun. Let’s think about that a little more. I found this chart in Lecture-Tutorials for Introductory Astronomy by Edward Prather et al.:

Month

Earth-Sun Distance

December

147.2 million kilometers

June

152.0 million kilometers

September

150.2 million kilometers

March

149.0 million kilometers

There are a couple of things I can learn from this. First, the Earth is not always the same distance from the Sun. Second: It is June now and we seem to be at our farthest point from the Sun. Wait a second! It’s hot now. It’s summer, right? Shouldn’t we be closest to the Sun?

The Southern Hemisphere has winter in June when the Sun is at its farthest point, but the Northern Hemisphere is enjoying summer in June. If the seasons were caused by our distance from the sun, both hemispheres would have to experience summer (and winter) at the same time. But we have opposite seasons, so the distance from the Sun can not be what causes our changing seasons. Well, then, what does?

We know that the Earth is warmed by radiation from the Sun – sunlight. The Earth is also tilted with respect to the Sun at about 23.5°, so that it looks like this as it orbits:

Sometimes the northern hemisphere is tilted toward the sun and sometimes it is tilted away from the sun. When the north is tilted toward the sun, we get more direct sunlight hitting us. The Sun appears to be higher in the sky in the summer when we are tilted toward the sun. Direct sunlight gives us more heat. Think about going for a walk in the summertime. Does the sun feel hotter in the middle of the day when it is directly above or in the early evening when it is low in the sky? The sun definitely feels most intense to me in the middle of the day. I tend to go on walks with my daughter in the morning and the evening.

This more direct sunlight gives us more heat and causes the change in seasons that we experience.

At the north pole, this tilt is enough that in the summer, there is always sunlight hitting the ground and there is no night at the peak of summer. The farther north you are (or south in the southern hemisphere), the more dramatic the change in light and temperature is. Near the equator, there is always plenty of direct sunlight regardless of the season and so the temperature remains warm year round. However, far from the equator, the amount of sunlight hitting the ground changes dramatically due to the tilt of the Earth and so the temperature also changes quite a bit from season to season.

The summer solstice on June 20 is the time when the tilt of the Earth and the rotation around the Sun causes the northern hemisphere to get the most direct sunlight. The sun is highest in the sky in the north and daylight lasts longer than any other day of the year.

So what does this all have to do with my front door? In the spring and winter, the sun is low in the sky to the south and so my front door gets a lot of direct sunlight. However, now that it is summer, the sun is high in the sky and the eaves on the house block the sun from hitting the door. Here is my silly exaggerated picture of this:

Phew! So I do not have to worry about my daughter burning her hand on the door. Of course, it is hotter outside and the sunlight is generally more intense, so I have to worry about other things like sun hats, sunscreen, sun shades on the car, etc. She is very fair of skin (like her mother) and will likely burn easily with the intense summer sun.

Jingle Cubes

We had some visitors come and stay with us last weekend. My daughter is really wary around strangers, so I was very happy that she handled the visitors so well. She relaxed enough to stop giving them the evil eye and went on to smile and play with them some. At one point, one of our visitors mentioned what a nice set of alphabet blocks she had and I was so confused. My daughter doesn’t have any blocks.

I looked up and responded, “Oh, you mean the jingle cubes.”

My husband and I discussed at one point that normal parents probably don’t refer to their child’s toys by the proper geometrical shapes. But these are clearly cubes:

And these very beautiful jingle cubes (they each have a bell inside them so they jingle when my daughter shakes them) were made for us by a mathematician, so I think we should call them cubes.

Of course, geometry has never been my strong point, so I may have to do some research if I want to continue this trend of calling her toys by their right names.

We definitely have spheres (left below), cubes (above), and cylinders (right below) of many different types. Here are a couple:

And of course, it will be important for my daughter to know that this is a ‘truncated icosahedron’: (Mathematica Website)

 It has 32 faces and is apparently also the shape used for soccer balls. So this seems important for her to know, right?

My daughter does not have a set of blocks yet, but we are hoping to get her a nice set of wooden blocks, maybe for her birthday. I think I may have to just resort to calling them blocks unless some of my mathematician friends can help fill in the empty place in my brain where geometrical shapes should go.

Of course, at some point, I think we should just call a giraffe, a giraffe and not worry about its shape:

For those of you who are physicists out there, you know that geometrical shapes are not really important since we tend to approximate chickens as point particles and cows as spheres. Anything else is too complicated for us.  For those of you who are not physicists and wonder why we care about chickens and cows…well, I am not sure I can explain physics humor, but we think it’s funny. Ah, my poor kid is going to be so embarassed by her mom.

The jingle cubes will always be jingle cubes, though. And they have been a favorite of my daughter’s for a long time. First, they were so big, she needed both hands to grab them and they helped her learn hand coordination. Then, she loved to chew on them (like everything else). Then, her hands grew and her coordination improved so that now she holds one in each hand and shakes them and knocks them together to make music. Maybe soon she will start to stack them, and then (in the distant future) use them to spell words. They really are fantastic, multipurpose jingle cubes.

Venus Transit

A couple of weeks ago, I wrote about the solar eclipse that was visible in the Western US. Unfortunately, the weather did not cooperate with my eclipse viewing. I think if I had really tried to see it, I would have been able to see something through the clouds, but there was also a tired and fussy baby involved in the equation.

For those of you who also missed it, a few of my friends posted some pictures of the eclipse on Facebook and gave me permission to share them here:

Partial eclipse in Chicago, IL. (Ivy Fitzgerald)

Annular eclipse through eclipse viewing glasses (left) and through the clouds (right) in Tokyo, Japan. (Amy Lovell)

Or if you’d like to see a time lapse of the entire eclipse, here is one of many YouTube videos.

While I missed the eclipse, there is another exciting solar event coming up: the Venus transit. This is very much like the solar eclipse, only this time, Venus will be blocking the sun instead of the moon. Of course, Venus appears much smaller than the moon to us on Earth, so instead of blocking the entire sun, Venus will just appear as a black dot moving across the sun.

Why does Venus appear so much smaller even though it is actually much larger than the moon? The apparent size of objects in the sky depends on the ratio of the object’s size to the object’s distance from us.

For example, the sun and moon appear to be about the same size in the sky from our viewpoint on Earth. This is why we can have a total solar eclipse where the moon completely covers the Earth. Looking on Wikipedia for estimates of sizes and distances, I find that:

This ratio is almost the same using some average, approximate values for distances. This is why the sun and moon appear to be the same size in the sky when we look up.

So how big will Venus be compared to the sun (or moon)? The Earth orbits the sun at a distance of ~150 million km, while Venus orbits at a distance of ~108 million km. So, when Venus is directly between the Earth and Sun (when we see this Venus transit), it must be ~32 million km away. Venus is approximately the same size as the Earth and so

So Venus will appear much smaller than the Sun. These numbers do not give me a good idea of what this will look like, but this picture from the Wikimedia Commons might help:

This is a fairly small dot, but definitely visible and I am excited about the chance to see it!

We have all probably been told from a young age that we should not look directly at the sun, so how are we supposed to view this transit? The sun is so bright it will actually damage our eyes. There are several different types of methods of looking at the Venus transit (or a solar eclipse) safely. A number of online stores sell “eclipse viewing glasses” which are really just filters that block the sun. The standard set of glasses appears to be made of Optical Density 5 filters. This means that the light that passes through the glasses is 105 (or 100,000) times less than the light that enters the glasses. You can still see the sun through the glasses, but it appears 100,000 times dimmer so it will not damage your eyes. Another good method is to use binoculars, or a telescope or other lens to project an image onto a piece of paper other surface. Do not look at the sun through the lens!!! This would certainly cause you harm! But, if you point the binoculars at the sun and put a surface behind the viewing lens, you will see an image of the sun that you can look at.

The Venus transit will be visible over much of the world, including all of the United States. NASA has a map of visibility if you would like to know if you will be able to see it and when. Click on Local Transit times in the bottom right to find out when you can see the transit at your location. We should be able to see it in the late afternoon/evening of June 5. I am hoping the weather cooperates this time so that we can go out and look! I even got some eclipse viewing glasses for the occasion.

This will not happen again in our lifetimes, so you should try to go out and see it. If you live in a part of the world where the transit is not visible, or the weather does not cooperate, NASA is also broadcasting the transit live from Hawaii so you can watch it on your computers at home.

UPDATE after the Venus Transit:

We were much luckier this past week in our solar viewing. The afternoon was partly cloudy again, but the Venus Transit started around 4 PM and lasted through sunset where we live, so there was a much bigger window during which we could try to find a sunny moment.

As mentioned last week, Venus looks much smaller than the Sun as viewed from Earth and so it was difficult to see the Venus transit just using eclipse glasses and our eyes. We may have been able to project an image using binnoculars or our little telescope, but do not have a fancy telescope and as always, have a little girl who had little patience with this watching the sky nonsense. However, we were able to see the Venus transit using our digital camera with the eclipse glasses in front of the lens. Here are some pictures my husband took:

These both show the image of the sun through the glasses, which filters out most of the light. The black dot is Venus moving between the Earth and sun. The image on the left was taken at 5:58 PM and the image on the right was taken at 7:12 PM. You can see on the right that the clouds have come in, partially blocking the light from the sun.

It was exciting to get a chance to see the transit since it won’t happen again until 2117. If my daughter lives for a very long time, she may get to see the next one, but I am certainly going to miss it!

Baby Thermometers

Babies have very limited methods of communicating what they want or what is wrong with them. Crying can mean any number of different things. At this point, I am fairly good at figuring out when my daughter is tired or hungry or upset about strangers or just bored. However, sometimes she just cries and gets very upset for no clear reason and it is difficult to figure out what is wrong.

A couple of weeks ago, my daughter was very fussy and needier than usual and just refused to nap. After a while, I decided that there was definitely something wrong and that she seemed sick. One of the main tools for determining if our child is sick is our thermometer. Being a scientist (or a geek, if you prefer), I am of course interested in how different thermometers work and how they measure my daughter’s temperature.

While it seems that there are a wide variety of baby thermometers – ear thermometers, rectal thermometers, under arm thermometers and forehead thermometers – the most common types fall into just two categories of operation. The rectal and under arm thermometers use contact between the skin and a metal component on the thermometer to read temperature while the ear and forehead thermometers use the radiation emitted by your baby’s body to calculate temperature. These thermometers use very different techniques to measure temperature than the bulb thermometer many of us grew up with.

Contact Sensors

The metal contact sensors are most commonly electrical sensors. There is a thermistor in the metal detector portion of the thermometer. This is a resistor that changes its resistance depending on temperature. To understand how this works, we need to think about some simple electronics.

Consider a very simple electronic circuit like the one below:

A battery provides a voltage – 9 Volts in this picture. A constant current travels around the circuit because there is just a single path through the loop. An ammeter is a device that is used to measure the current – this is a measurement of how much charge passes through that point in a given amount of time.

Ohm’s Law tells us that voltage, V, is related to current, I, and resistance, R, as follows:

So what happens when my resistor is sensitive to temperature? When you put the resistor in contact with your body, it heats up and its resistance decreases. The battery voltage stays constant, so as the resistance decreases, the current through the system must increase. This makes sense, right? If there is less resistance to the flow of charge, more charges will pass the ammeter in a given amount of time.

By measuring this current, and knowing the voltage of the battery, you can easily calculate the resistance of your temperature sensitive resistor using the equation above. The resistance vs. temperature is something that is very well known by the manufacturer, so once you know the resistance, you know the temperature of your baby who is in contact with the thermometer.

The circuit in your thermometer has a few more components, but this basically how it works. And it does all the calculating for you and just displays a temperature.

Infrared Sensors

If you bring your child to the doctor’s office, they will likely take his or her temperature using an infrared sensor. This is what my nurse uses. She takes a device with a flat, round end and lightly moves it across my daughter’s forehead and reads out the temperature. This is very fast and is great for a kid (like mine) who hates to be touched by strangers.

How does this work? If you remember, a few weeks ago, we talked about Blackbody Radiation. Our bodies emit light, but it is in the infrared where we cannot see it with our eyes. The peak wavelength emitted from our bodies is about 9 microns (Check out the PhET website to see for yourself). The amount of light and the peak wavelength of the light both depend on the temperature of our bodies.

The thermometer uses a thermopile to measure the radiation coming from our bodies (How Stuff Works). Heat from our bodies heats two pieces of metal that make up the thermopile. A voltage is created between the pieces of metal that depends on the heat of our bodies. (Wikipedia)

How do we measure this voltage and turn it into a temperature? We could use the same circuit that we used above. This time, have a constant resistor and use the thermopile as our voltage source. We can measure the current to determine the voltage created by the heat from our bodies and determine the temperature from that voltage.

The infrared sensors are very fast, which is definitely a plus with a screaming, squirmy baby. Both types of thermometers work best when the temperature is taken inside the body – a rectal thermometer or ear thermometer. However, we were discouraged by the hospital from using a rectal thermometer on a newborn because they said it is to easy to cause them harm because they are so tiny. And ear thermometers can be a little tricky because they need to be aimed at the baby’s eardrum to get an accurate reading.

We have one of the forehead thermometers at home so I definitely wanted to make sure I understand how they worked. It turns out my daughter did not have a fever when she was sick a few weeks ago. I did take her to the doctor, though, and she did have an ear infection. The poor kid was sick for a while since the first set of antibiotics did not work on her, but is feeling better. And is now fussy for some other completely unknown reason…

I hope my daughter continues to be healthy and not have any fevers, but I do think it is interesting to know how current thermometers make use of technology to help me figure out what is going on with my little girl.

And, of course, I am looking forward to the time when she can tell me what is wrong and there is a lot less guesswork in trying to figure out if she is sick.