Who Am I and Why am I here?

My name is Steve Maloney and I have been teaching Chemistry Physics and Earth Science for twenty five years now, the last fourteen at Duarte High School.  I have always emphasized laboratories, scientific process and have a philosophy of attempting to impart translatable skills along the way.   This summer I had the honor of being selected to join the IQIM program and as part of that program I worked with Rana Adkhari’s research group which from what I can gather, seeks to reduce sources of noise (enhance signal quality) to better detect signals which indicate warps in space time for the LIGO project.  (Laser Interferometer Gravitation Wave Observatory)

As a high school science teacher, when covering the developmental history of the current model of the atom, I include several themes:  a) the importance of being well read (keeping up with what is going on in academic circles of interest to you)  b) publishing your findings (so that others can replicate or interpret your experiments) c) progress also depends on technology, (as technology improved our ability to observe certain phenomena improved).  d) control when making a hypothesis make sure one is testing or changing only one variable at a time: eliminate all possible sources.

What is LIGO

LIGO is an NSF founded project led by groups at Caltech and MIT whose purpose is to measure gravitational waves.  A gravitational wave can be detected by measuring length change along perpendicular arms of a 4 km long L shaped apparatus.  In Advanced LIGO, the next generation detector scheduled to start operation in 2015, a 500 kilowatt laser beam will shoot down both perpendicular arms simultaneously coming from a single source known as the beam splitter.  Mirrors on the far end and proximal ends serve to let the light bounce back and forth resonantly amplifying the signal to detectable levels.  When the signals from both arms are locked, there is complete destructive interference so that when the two beams arrive at the photo diode detector no signal is detected.  Since the speed of light, (C), is a constant regardless of reference frame, as a gravitational wave passes, the lengths of the X and Y arms change as predicted by the theory of general relativity in different amounts and the arriving wavefronts no longer cancel completely out.  Thus a signal has arrived, indicating a warp in space time.  The length of the arm does not change by much at all.  Now we come to the difficult part; knowing the distance between the two mirrors.  As the gravitational wave passes, the length of the 4 km arm changes by as little as 1 x 10-20  m.  For a little perspective, that amounts to about 1/100,000 the width of a nucleus of an atom.  All kinds of controls have to be taken to prevent mirror sway, (seismic isolators being the main one).  Mirrors can also change shape when the laser beam hits them and warms them up.  Conversely, more powerful lasers provide greater signal strength.  Systems have been devised to heat up the mirrors in such a way as to cancel out any shape changes due to heating by the laser. In order to reduce noise, mirror surfaces have to be ground and polished with a tolerance of no greater than 1 angstrom (1 x10-10 m) Light needs to reflect back exactly uniformly with an absolute minimum of scattering so as to prevent any stray radiation from getting into the vacuum chamber ( 1x 10 -9 torr).  Minimizing noise also means the internal structure of the mirror needs to be as close to perfect as current technology allows.  And that is where the light scattering  experiment I  have had the privilege of working with Jan Harms  PhD comes into focus. (pun intended)

The Experiment:  Comparing Light Scatter from a Plane Mirror of three Different Wavelengths, 623nm, 532nm, and 405 nm.

On the day of my arrival, my Physics knowledge were quickly put to the test. Little did I know that scientific process skills were to be used every day for the duration of the experiment.  Jan wanted to replace the battery of the laser with a plug in DC source.  He showed me a calculation where he could plug in the source voltage and obtain the voltage drop at each resistor.

V1 = v x R1 /R1 + R2

Once the source of power was constant and not diminishing as in the case of a battery we set about eliminating the next possible variable; Focus.  We could not find a diverging  lens of correct focal length inside the LIGO workshop, both lenses on hand had focal lengths that were too long.  So the optics equation was employed;  1/f = 1/f1 + 1/f2 .  Next came the problem of removing stray radiation.  (might give false results!) Damps were deployed, (shown below) wherever reflected light interfered with the experiment

        

  

Irises were arranged in line with the laser beam to assure identical size and  placement of beam on mirror for all three colors; red (623nm), green (532nm), and purple (405 nm)  A trial run was almost ready.  An electronic CCD camera connected to the computer was then hooked up and attached to a 40 cm long rotating aluminum arm, a lens was placed in front of the camera at correct distance, (thank you optics equation). A plane mirror was placed from our best guestimate at the center of rotation.  See photo.

Trial photographs at increasing angles (towards normal) showed images of point defects migrating from right to left across the screen.  This led me to conclude that the mirror was between the axis of rotation and the camera.  With repeated testing, we finally got mirror surface at exactly the axis of rotation, (migration of image stopped)  Once again we removed another unwanted variable.  All the while, over the course of the improvisations, Dr. Jan Harms was sharing his thoughts and intentions, communicating his progress,  or lack thereof, on the Richter Elog for all concerned parties.  Aha!  Another important part part of the scientific method, communication!  One day, I was invited to join Jan Harms, PhD and Rana Adhikari, PhD, for lunch.  Dr Adhikari had a few questions and suggestions for Jan that they discussed over lunch.  I then had my AHA moment, universities such as Caltech, are hotbeds of innovation because people with very specialized knowledge can get facetime, (even more important for progress than more modern means of communication).

The Analysis

At last, we were ready to take some pictures that will be fit for analysis.  Here are some MatLab analysis, of the mirror surface code written by Dr.  Jan Harms,


 

Angle 11 Purple

angle 11 red

In the two images above red and purple both seem to behave similarly as evidenced by the bright spots.  Lens aberations are clearly responsible.  Two possible  sources of lens abrerations are lens outer coating roughness or point defects.

Lens scattering luminosity is a function of the sin of the incident ray as depicted in the graphs below

 

Purple BSDF

 

Red BSDF

 

 

 

 

What Will Become of the Experimental Findings?

Jan Harms, PhD, when asked how expected to use the information gleaned from this experiment, said when the data for the green laser comes in, hopefully something can be learned from a comparison of the purple, green and red  wavelengths and perhaps the information may be extrapolated to lead to a greater understanding of the action of infrared at mirror surfaces.  If the analysis finds something compelling, optical manufacturers could get some feedback about how to improve their manufacturing processes and outcomes.

What other uses can improved mirror manufacturing have on the economy?

High quality images and mirrors are in demand for military imaging.  Mirrors and fiber optics also have spillover benefits in quantum cryptography, and quantum photography.

 

What impact will this impact have on the way you teach Physics and Chemistry?

The importance of computer skills, namely, the MATLAB program was a real eye opener for me.  I also learned that the world wide web is accelerating the pace of innovation because of improvements in communication.  Dr. Jerry Pine, also taught me about the Khan Academy and the “Flipped Classroom” that it helps facilitate.  I will include more laboratories where students will be making their own graphs using Excel Spreadsheets.  Most importantly, I have made many contacts while at Caltech this summer and look forward to having captivating guest speakers in my classroom this year!