Constructing an Extended Cavity Diode Laser
An REU project (currently) being done by Ryan
Price
Supervisor: Dr. DePaola
Welcome to
my 2008 REU research page. The following is a quick summary of a work currently
in progress:
Project: Over the summer, I am tasked with
constructing an extending cavity laser (ECL) that will be used within a
magneto-optical trapping configuration. For more information until I write a
nice general description, see wiki: Magneto-Optical Trap.
For the basis of our design, a reference paper concerning an extended
cavity diode laser built for Cs laser cooling is used as a starting point.
Because the experimental setup here at KSU uses Rb atoms, this requires a
re-engineering of the design to fit our specifications. So, essentially the
design and construction of the refit laser is the task at hand.
6-6-08:
The
following is a quick outline of the (presumable) steps involved in the laser
construction
1.
Researching
/ Basics of design
2.
Redesigning
for Current Experiment
3.
Parts
Acquisition and Construction
4.
Calibration
and Testing
During the
first week of working on the project, the first steps taken were to approach
step one through trying simple redesigns of the model ECL and looking for the
parts required for the project. By doing such I have a much better grasp on the
requirements and functionality of the laser model I have been tasked with
building.
6-13-08:
Week two so
far has been the creation for detailed designs on the computer. These models
created are going to be the reference model used during the machining and
construction stage to get the right dimensions and angles (mind you, optical
devices are particularly picky about exact geometries). If all goes well, parts
will start to be ordered and come in next week. However currently there is a
hold up in the process. Two parts required cannot be found easily or cheaply
for purchase so alternative sources for such parts may be found to keep the
project rolling on.
Oh yeah, and
a tornado hit the physics building… how cliché for a
summer in Kansas.
6-20-08:
Week three
is design week! I’m (slowly) learning how to use 3d tools to help model the
main casing to my laser design
My first day
trying to use this program, or as Dr. Weaver says jokingly, “Something to be proud
of (like) in kindergarten”.
And then
things have progressed now to where someone in flatland would be proud!
Ok well then
let’s try again and try harder…
Now we have
3D! If only this were the end of the story. In the above picture, you can see
almost all the parts involved. For example, the big red block on the back is
the laser diode mount the green tubes are PZTs and the red thing below them the
prism that they control.
6-27-08:
So, because
of the tornado that hit us, the building had broken windows.
And because of broken windows and loose insulation, there is an asbestos fear
in the building that caused a building closure for 2 and half days. Kansas
seems to be the most eventful place I’ve worked thus far with tornados, power
outages and asbestos scares. So all together, not much progress was made in
updating the laser design unfortunately.
However, our
research group had time for an experiment run using the Kansas Laser Source (KLS) and I
got the opportune chance to watch (and help on a few parts!) the setup of the
experiment. It should be noted that being able to help out with operation in
KLS is quite the honor to me, considering the beam if brought to focus can
ionize air at a point (to the non-physics inclined, a familiar form ionized air
that you may be familiar with is lightning which has the ability to ionize the
air because of the enormous electric field created during discharge). Anyway,
as far as the laser goes, purchasing of parts is starting now, so hopefully construction
will be underway soon.
7-3-08: Parts, parts, and
more parts…
First, the
laser design itself is finished and en route to being created in the machine
shop. Note that the design has gone under many (minor) revisions. The most
important lessoned learned here is: never design in the metric system if
submitting items to a machine shop. So, introducing the final design:
Secondly,
ordering parts has a downside. Especially when you get a prism that looks like
this:
When it
should look like this:
And why is
this prism a problem? Consider a light beam incident on the hypotenuse face and
an arbitrary location:
The purpose
of the prism is to act as the retro-reflector in the Litmann ECL design. So
with a large chunk of my prism missing (purple above), light that comes in at
this location or on the opposite side equidistant from the center of the face
is not reflected back properly. This is awful for two reasons:
1.)
The
laser power output will be significantly lowered
2.)
Nobody
makes prisms in nearly similar dimensions and thus there are no other prisms in
the entire land of the internet to be had to replace this one.
So in
summary, these prisms were promptly sent back to the manufacturer, and their
customer service I’m sure were simply thrilled to talk to me.
7-11-08:
Now that the
main casing for the laser will be made in the shop soon, I got head to the shop
myself to make an accompanying piece. Specifically, the one that holds the
laser mount to the case. More specifically, it is a flange that allows the
laser mount to be rotated such that the outgoing polarization of the laser
light incident upon the diffraction grating can be changed in such a way that
it controls the amount of light diffracted versus reflected. This in turn
controls how much light is kept in the extended cavity versus sent out of the
ECL.
So my
project this week was to start with something like this:
Throw it on
a lathe, put it through a saw, cut my finger, and drill some holes… and presto:
This piece
stands as a testament to my luck in the machine shop.
And because
of unfortunate happenstance, our project is somewhat on hold because the
specific type PZTs that control the prism rotation cannot be found at a
reasonable price. And one of the two companies that do sell them won’t even get
back to me with a price quote, even if I call them. Great customer service, I
do say.
And speaking
of customer service and shameless advertisement, an order from Thor Labs came today and in it, to my
surprise, there was a box full of ‘Lab Snacks’ with candy and food of all
kinds. Supposedly such a delightful thing comes with all of their shipments. After
dealing with other companies and their rotten prisms and not returning phone
calls, this really makes one’s day. Thor labs made a future customer out of me
by such a gesture, as trivial as it may sound.
7-18-08:
Our group
had another experiment using the KLS during this week, so for a few days I was
in and out of the lab watching/helping to set up parts of the experiment.
And last but
not least, the replacement prisms came back and they are exactly as horrid as
the first batch. The sales engineer tells me that ‘such deviations are common
from original specifications’. I agree, a five percent difference might be ok
to slide by, but when the dimensions are off by at least a quarter of the
advertised catalogue, then that’s just plain negligence. As it is closing in on
my last few weeks here at KSU, there is no way that I can get a replacement
prism custom ordered, so what to do is really up in the air.
On the
machine shop note, I got to finish a portion of the sub-assembly that holds the
prism
Oh yeah, and
I have my main assembly too:
Now just to
put it all together…
7-25-08:
This week
has just been finishing up work in the shop and starting work on the electronic
sides for the laser diode mount. Thus far I have cables and am ready to go in
terms of connecting the cables and mounting the (really expensive) laser diode.
Final
Presentation and Report: An overall summary
of the work should be done around the end of the summer (beginning of August)
Pictures!
Other
Projects and Papers:
Although not the groundbreaking by any means, the following are some
papers I’ve had to write for various classes during my undergraduate career at
the University of Arizona Physics
Department.
Perhaps to someone they may provide some value or reference:
Spring 2008:
Measurement of Planck’s constant through Black Body Radiation
Analysis
Measurement of the Sodium D Emission Lines
Using a Michelson Interferometer
Fall 2007:
Experimental Determination of the Speed of
Light by the Foucault Method
Fall 2006:
Effect
of Matter Density in the Evolution of the Universe
Other Stuff (Lectures and such):
World wide internet:
JRM Laboratory (Home sweet home for
2 or so months)