# Journal

## August 3, 2007

Well, this is my last entry. The REU program is over, we all gave our presentations earlier, which went very well by the way. I had a great time this summer. It was a great experience working and learning in the laser center. I had a lot of fun, everyone here is really friendly and great to work with. Bye everyone!

## July 27, 2007

Laser Sam was here for a couple days this week. On Wednesday, he gave a talk on various types of lasers. Yesterday, he helped me improve the ammeter I built, which was working, but not reading completely accurately. Today, I will be building the analog voltmeter that I need.

## July 20, 2007

I spent some time today putting a shunt on the analog ammeter so it will have the correct scale. This is basically a current divider. Without the current divider, the meter reads from 0 to 1 mA I want it to read from 0 to 10 mA. So, I needed to spilt the current so that only one tenth goes through the meter.
P.S. Yesterday I measured the width of Hamsa's hair. It was only 48 microns wide!!

## July 18, 2007

I spent the last couple of days scrounging for parts to put in my circuit. Yesterday, I took apart an old circuit so I can reuse the resistors. They are a 20 MOhm and a 99 MOhm. Today, Dr. Noe and I found some old analog meters that we think will be better to use than digital meters.

## July 11, 2007

I measured the width of one of my hairs today. When you place a hair in the path of a laser, it creates an interference pattern just like when the beam goes through two slits. The edges of the hair act as the two slits. By measuring the distances from the center of the maxima to the central bright spot, you can do some calculations and determine the separation between the slits, or in this case, the width of the hair. My hair is about 70 microns wide. This is about average for human hair.

## July 10, 2007

Yesterday, Ian and I played around with the open cavity laser. By making fine adjustments to the angle of the output coupler we were able to see several different modes. One was a very nice doughnut shape with a nicely defined center. We also inserted a hair inside the laser cavity to get different modes. We had to use Ian's hair because when we tried my hair, it was so thick it kept the laser from lasing!

## July 9, 2007

I am going to continue my exploration of HeNe lasers. I'm hoping to get my hands on a variable current power supply so I can look at the power output versus current. I also want to study the noise of a laser.
I want to measure the current output of the power supply that is not marked. In order to do this I need a hermaphrodite Alden connector. Dr. Noe is trying to order one from a company in Ohio, but no one was answering the phone last week. Maybe we can get a hold of someone this week.

## July 3, 2007

Obviously, I didn't get around to updating later like I said I would, but at least I didn't wait as long this time to post a new entry. Maybe I'm getting better at this, you never know.
Anyways, my talk on polarization went fine, the high-schoolers seemed to get a lot out of it. Soon (AKA eventually), I'll post my slides on my website. Yesterday, I spent a lot of time figuring out what voltage and current each of the lasers need in order to work best. I also tried to find the voltage and current output of our power supplies. This was difficult, because most of our equipment, lasers and power supplies, are older and have out-of-date model numbers. This means you need out-of-date catalogs to get the spec sheets. I did manage to get find what I needed for all the power supplies except for one which has no model number. There is one power supply that we thought wasn't working properly turns out to just have a lower current output which makes it just about perfect for our smallest laser.

## June 27, 2007

It's been a while since I updated this...oops. Well, this week the high-schoolers arrived. We've all been pretty busy preparing talks for them. I will be giving a talk on the polarization of light. I'll try to add a little more later.

## June 19, 2007

This first week at Stony Brook has been an interesting one. The first day, we were using a magnifying glass to burn paper by focusing sunlight. We tried to do the same thing with a lens from a pair of reading glasses, but it didn't work. We knew the paper wouldn't burn because we couldn't focus the sunlight to a small enough spot the way we could with the magnifying glass. What we didn't know was why we couldn't. We were also confused as to why the spot changed shape when we were near the shadow of the building behind us. It wasn't until a couple of days later when we were back outside trying it again that we figured it out. We were using the magnifying glass to make a spot on the ground when we saw some miniature clouds float by. We realized that what we were seeing on the ground was not just a collection of light rays, but an actual image of the sun. We couldn't get it any smaller because the sun is a finite size. The reading glasses have a longer focal length than the magnifying glass, so the spot (image) was bigger.

Meanwhile, back at the lab, we played with the thin lens equation. We set d equal to the sum of the object distance and the image distance. We eliminated the object distance and solved for the image distance. (This can also be done vice versa.) What we got was a quadratic meaning there were two possible images. When you think about it, this shouldn't be surprising. If you switch the object and image of a thin lens, it doesn't change anything. So, there are two object distances and two corresponding image distances.

More to come soon!

 Mallory FischerJune 2007 Home  Laser Teaching Center