Physics and other weird things

Last week I was able to set up the Michelson Interferometer correctly and obtained the desired annular interferences. This is a huge accomplishment to me because I had been having so much trouble aligning all the optical devices.

The biggest issue I was having is that I have never had this much exposure to optical devices before. Sure, I did have some experience from a class but it was much simpler than this real life application work I am doing in lab now.

For example, an obstacle I had to overcome was that the height of the adjustable mirror was bigger than the height of the beam. Below is a diagram of how I fixed this issue:

First, I placed a mirror at 135 degrees ( if you were looking at a unit circle) and made sure that the reflected beam was well aligned. Then I placed another mirror at 45 degrees and made sure that the twice reflected beam was well aligned as well. Using the knobs on the mirrors that introduce angle shifts, I aligned the reflected beam to be at the center of the adjustable mirror.

My new input would be at an appropriate height. From here on out I just calibrated and aligned the rest of the Michelson Interferometer.

The number of fringes depends on the difference in path lengths the two arms go through. As a reminder, here is the diagram of the set up:

The number of fringes observed decreases as the difference in distance of m1 and m2 from the beam splitter also decreases. In other words, if m1 and m2 are at the same exact distance from the beam splitter then we will have very few fringes.

If we introduce the phase plate just before the m2, a different path length would be traveled through the pi part and the 0 part of the phase plate. This is because the pi part of the phase plate has an additional deposition, which means an additional layer the light must pass through. So what we would expect to see is annular fringes that are not symmetric.

Here is what was observed:

This is exactly what we were hoping for !! but we also encountered some other strange interferences.

Like this one:

The interference pattern shown above was off to the right of the main interference we were looking for. We tried to look for the source of it, but we could not localize it.

here is a better image of it:

We can see that on the persons hand to the left some additional interference patterns are showing.

We are not sure where these additional interference are coming from, but a while ago when I was doing my power and polarization measurements I noticed something interesting. When the laser beam was incident onto the phase plate, the output light on the pi-phase had dispersed. Instead of only seeing one beam, I observed a main beam of light and a couple of other ones next to the main one. They were pretty intense relative to the main beam since I was able to see them with the OD glasses I was using.

We made a note of this, but maybe this is where the additional interferences are coming from?

The graduate student I am working with also mentioned something about light coherency and that a possible solution would be placing m1 and m2 farther from the beam splitter. At a much bigger distance than they are now. I am not completely sure how this works out, but I do plan on getting some clarification.

That’s it for now folks,

Till next time !

It has been about 4 work days since I have attempted to align the Michelson Interferometer. It took a lot of tedious little adjustments to finally get it to work but I think I did it !

Here is a very simple diagram of the set up and of the different interference patterns that can be created:

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Let us talk about the set up shown in Figure 1. First, the light beam gets split up approximately 50% and 50% (red light ray) . A fixed mirror, m1, is then set up perpendicular to the beam so that the light beam traces back where it came from (green light ray) . The angle of the beam splitter also causes half of the light to get reflected on to a screen. An adjustable mirror , m2, is also set up so that it is also perpendicular to the red light ray. Half of the light gets reflected back to the light source and half transmits through the light beam and is incident onto the screen ( blue light ray) . I also used a lens to expand the beam before it went into the beam splitter!

The light beam gets split into two parts initially and then brought back together at the screen. The difference in path lengths of the two beams causes an interference pattern.

The thing is that if m1 and m2 are not exactly perpendicular, then the output interference will be as shown in figure 2 labeled b. The interference will be horizontal or vertical straight fringes. if the 2 mirrors are exactly perpendicular to each other we will get annular shaped interference.

Trying to get the two mirrors to be exactly perpendicular WAS SO HARD!! I spent hours trying to align them. I finally did it C’:

Here is the interference pattern I was looking for:

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Isn’t it beautiful c’: ? It is not perfect, as we can see not all of the rings are in the view of point. To fix this, the angle of the beam splitter was adjusted. I also need to make sure that m1 and m2 are at the same distance from the beam splitter.

This is the feedback I got from my graduate student and my advisor but besides that everything is looking good !

I am kind of nervous about moving the mirror to make sure that they are at the same distance because I do not want to introduce an angle shift between the two mirrors :c

which me luck y’all !

On my last rushed post I talked about this so so “simple” set up to help characterize the binary phase plate. I soon realized that there is a great difference in theoretically simple but experimentally really difficult.

So let me start from the beginning, I should probably show you guys what the so called phase plate looks like. A picture of it does no justice to what it actually is so I have also attached a drawing of it.

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The photo on the left shows the actual optical device and the photo on the right shows my little sketch of it. We will talk about the image on the right. The phase plate is separated into two parts, labeled 1 and 2.

Phase Plate: The Part Labeled 1

The part labeled 1 on the phase plate is made out of quartz and the index of refraction is known exactly since it is commercialized and sold on the market. When light passes through this section it remains unchanged. This means there is no phase shift introduced.

Note: The index of refraction is a way to measure how light bends when it goes from one medium to another. For example when the light ray goes from traveling in air to traveling through the quartz plate.

Phase Plate: The Part Labeled 2

It is hard to see in the photo of the actual optical device, but the part labeled 2 has a green tint to it. This is because there is a deposition, or added layer, on top of the commercialized quartz. I am not sure what the deposition is composed of but I do know it is suppose to introduce a phase shift of π (pi) on the incident light wave.

The deposited area was made by an engineer that works for one of the engineering schools in Paris. Since it is homemade, there might be error. For example, the phase shift introduced might not be exactly pi. The thickness of the deposited area ( section labeled 2) might not be exactly the targeted value that was calculated. The deposited section might also not be homogenous, meaning it is not evenly distributed through out the surface. These are all the things I need to experimentally determine and characterize.

Power Distribution and Polarization of the Phase Plate

To make things clearer, I will be calling the green section of the phase plate the π-phase and the clear section the 0-phase. 

The first thing that I characterized about the phase plate was the power distribution and polarization on the π-phase and compared it to the 0-phase.

Polarization is just fancy way to talk about the direction of light ( in a super simple way ) 

In order to do this I set up a very simple experiment. All I did was pass a laser beam through the 0-phase and π-phase. I measured the power of the beam before entering and also the power once it passed through each phase individually. I also measured the power at various positions throughout each phase individually. I did this to see if the power output would be the same throughout different positions of the phases.

Not surprisingly enough, the 0-phase had the same power output at different positions throughout the whole 0-phase. This is not surprising because it is a piece that is commercialized, therefore the company needs to make sure all the products they sell live up to their expectations. The polarization also remained constant throughout the 0-phase.

The π-phase on the other hand had a very uneven power distribution. This means that as the position on the π-phase changed the power output also changed. Although the power was not constant throughout, the polarization was not directly affected.

I took data and coded it up using mathematica to make it look pretty and to show my advisor. I will also show it to you guys.

On the Image shown above you can clearly see that there is a big difference on how the power is distributed on the pi part compared to the 0 part.

The mean, or average, power on the π-phase is 9.87 mW. The standard deviation is about 0.603586, which is pretty huge.

Next I modeled the polarization.

The image shown above is the angles of light extinction when I used a polarizer. If the angles of light extinction are around 0 and pi then we can conclude we have vertically polarized light. The input light is vertically polarized, and we expect the output light to also be vertically polarized. Everything looks good so far.

The dashed lines correspond to the Pi phase and the solid lines correspond to the 0-phase. We can see that even though the deposition on the π-phase is not homogenous, the polarization is not effected much at all. There is a little bit of deviation, but not big enough to be a problem.

Why is the Mach-Zehnder Your Enemy Though ?

So based on the data I have collected, we can start looking at other parameters. So the next step was going to be to experimentally determine the thickness of the deposited section and to determine the exact de-phasing. Our first experiment didn’t work out, so we thought the Mach-Zehnder was the answer to all our problems.

Basically, a beam splitter is used to separate a beam and then another beam splitter is used to recombine the beams. When light gets reflected from a surface that has a higher index of refraction than the index of refraction in which the light is traveling, the light wave gains a pi phase shift. This is not true for the opposite case though.

So at the first beam splitter, the light gets reflected and gains a pi phase shift ( the green path). On the blue path, light gets transmitted and does not gain a phase shift. If we continue this analysis, we will see that at point B we will have destructive interference and at point A we will have constructive interference.

So, If we introduced an additional pi phase shift with our phase plate after the first beam splitter there will be constructive interference at point B and destructive at point A. That is, if the phase plate was constructed perfectly and it introduced a perfect pi phase shift.

The Mach-Zehnder Interferometer would be a way to classify both the de-phasing AND the thickness of the deposition. Theoretically, everything seemed to be working just fine.

That is until I came into the lab and tried to set up the experiment. The issue is that everything needs to be perfectly calibrated and that takes a whole lot of time. All the optical devices need to be relatively at the same angle. If one is moved, all the other optical devices also needs to be moved. I spent about 3 days trying to calibrate, yet it felt like I was making no progress.

So after talking with my advisor, we have decided to change the experiment once more. I will now try to recreate the Michelson interferometer. I have to do some research about how to do this and try to do it SOON since the internship is over at the end of the month. It seems like a little bit of a time crunch, which makes me a little bit nervous.

The thing about the Michelson interferometer is that it can only help me characterize the thickness of the deposition directly but won’t help me figure out the de-phasing directly. Another task I have to finish is to try to experimentally determine the index of refraction of the 0-phase and π-phase using Fresnels equations and some power measurements. I already tried to do this, but failed terribly. So second time is the charm?

It has been 4 weeks since I first started doing this research internship at IGOS. The first week or two I spent learning everything I could about wave guiding and our original experiment. I needed to do a lot of readings since I had never worked on optics outside of class.

So the whole Idea is that we are trying to convert the fundamental mode of light into higher order modes of light that we can apply to a process called parametric generation.

Parametric generation is the process where we will input a laser beam at a given wavelength into a nano-fiber and get a different wavelength output. Different wavelengths means different color. The difference in wavelengths is a result from the evanescent field created when part of the light wave inserted into the nano-fiber “spills” onto the outside of the nano-fiber. With the addition of ethanol on the outside of the nano-fiber, the photons will give some energy to the surrounding molecules. A change in energy directly affects the wavelength value.

There is a binary phase plate that was created by one of the engineering schools so my job is to characterize it.

Our first experiment consisted of a set of QWP and a binary phase plate which introduces a pi dephasing. The idea was that if we start with vertical polarized lights, convert it to right circular polarized light with a QWP, and introduce a pi dephasing in half the beam then we would have right circular polarize light and left circular polarized light in the same beam. Then we would use another QWP to convert those into linearly polarized light. The goal was to obtain vertical and horizontal linear polarized light in the same beam, which initially we thought would be achieved with the above experiment. The combination of these two polarizations inside a fiber create higher order modes.

Before I could characterize it, I was asked to prove this experiment mathematically using Jones matrices. After banging my head on the desk for a couple of days because the math was not working out I decided to ask for help. It turns out that the math wasn’t working out because our theoretical idea of the experiment was flawed. The binary phase plate needed to introduce a pi dephasing between the x and y components of the circular light. In our experiment it only introduced a pi dephasing between the two halves of the beam. This means that the light would still be circularly right polarized, but one half of it would start ahead by pi. Therefore, we needed to think about another way to characterize the binary phase plate.

So here comes the Mach Zehnder Interferometer. The idea here is that we set up an experiment with 2 sensors at the end. At one of the sensors there will be constructive interference and at the other destructive interference. If at some point, the pi dephasing is introduced with the phase plate, the the constructive and destructive interference will change places. This works out great theoretically if everything works perfect and the phase plate was perfectly built.

This is not the case. So my job now is to characterize the phase plate using the Mach Zehnder Interferometer and to try to figure out the best way to use the phase plate.

I have taken some data from some experiments I have done and I will be presenting it to my advisor soon. A more detailed blog post will also be coming soon !

I have had rough weeks before- heck, I’ve had rough months. But this week has really been something… special.

Life really has me coming home, laying straight on my bed, staring at the ceiling and weighting out in how much trouble I would get to get a direct flight back home to my momma. (If any of the program advisors are reading this hehehe I won’t do that)

I usually have environmental allergies around this time of year, so I wasn’t surprised when I started experiencing terrible allergies in Paris. I tried to postpone buying allergy meds because my days are super busy and I’m broke. At some point I gave in and bought allergy meds and I spent almost 20 freaking Euros on over the counter crap.

So I keep taking these meds and yet I seem to not be getting any better. All the allergy meds were doing was making me extremely sleepy. We had a 3 day weekend and I literally spent every day, all day sleeping. LITERALLY.

At some point ( Thursday of last week to be exact ) I thought I was actually sick. I spent nights coughing like crazy and getting almost no sleep. So I go to the store and get lemon and ginger to make teas because at this point I’m thinking I gotta be sick. I also got some Vaporub because my mom think it literally can cure anything.

Friday morning comes around and I wake up from my sleep unable to breathe. This happened almost every night since then. I’m trying to find doctors in my area that speak english but it seems almost impossible. Still, I try to ignore it and move on with my life. Huge mistake.

Tuesday morning comes around 0 sleep in my body, I decide to go to the emergency room because you know what? maybe I do want to breathe after all.

Turns out I had been having an allergic reaction to who knows what ( they said pollen or dust?? ) for 4 days. So I spent all day in the hospital alone freaking out about how much they will charge me for this visit. After 3 breathing treatments, inflammation/pain meds, chest X-rays, and another exam which I have no idea what it was because of the language barrier I was discharged.

They let me go without charging me anything, or I just misunderstood and walked out. Point is they gave me a prescriptions for some medicine which cost me 65 EUROS. 73 DOLLARS.

Yall…. 73 dollars hurt my heart and bank account.

So I come home and decide to have air and water for dinner. ( just kidding I actually had meal prepped lunch the day before). I actually get some good sleep UNTIL I woke up because I had to pee.

At this point I’m already bothered so I’m laying there wondering if I can just hold it till the morning.

I get up and get the key card that was given to me which gives me access to my room/bathroom/dorm.

My key card wasn’t letting me get into the bathroom, so I go to one that was already open. I’m like “huh that’s weird but brush it out the way. I finish doing my business and I’m walking back to my room and realize my key card wasn’t giving me access to my ROOM. Im out in the hallway in mini shorts and a tank top. its almost 1:00 am and i’ve spent all day in the emergency room. This is not the time or place for this to happen.

I sat on the floor by my room just really contemplating my life. The reception desk is closed. My only thought is to go to the security’s office, hoping he would be there. The office is like on the other side of the dorm residence. There is a good amount of buildings and walking there would be a mini mission.

So I wipe the tears out of my face, go outside and willingly lock myself out of the dorm building ready to find the security.

As I get outside, I decided that I value my life and I really do not know what kind of ghost/demons are out there. I try my card and it MAGICALLY WORKS AGAIN. I make it to my room and decided I’m never leaving it again. Disappointed but not surprised because I couldn’t sleep the whole night.

So then I get up and I’m like “ok just because I had a terrible day and night doesn’t mean that I can’t have a good day” . So I put some nice clothes on and get ready for work. There is these Navigo passes that cost around 93 dollars for monthly access to all public transportation in 5 zones here in Paris.

You have to swipe the card to actually go down to the train/subway (?). Lucky me, It wasn’t letting me go through. Some guy noticed me struggling and mumbling to myself and he swiped me in. I’m falling asleep all day at work trying to learn about Mach Zehnder interferometer and finally it’s 5:30, time to go home.

I make it to the station and the card WON’T LET ME IN. There was a security making sure everyone scanned their card, we will call him asshole from now on. So I approach asshole and ask him with broken french if he spoke English. He didn’t even look at me. He mumbled something. I go in front of him and gesture for him to come with me so I can show him my card isn’t working.

Asshole murmurs something and dismisses me. I try to show him on my google translate app what I am trying to say but he is clearly not interested in helping so I am standing there like:

So after going to the main office and asking for help my card decides to MAGICALLY work again. I am holding in my tears of frustration but I am just glad I can finally go home.

And long story short kids, don’t trust technology. It has been such a freaking rough week it feels like I have lived it so long and it is only Wednesday.

So like any healthy coping mechanism, I decided to come rant about it to the internet.

Paris is also such a populated city and my days are so busy it is hard to get some self reflection/self care time. This is something that really improves the quality of my life. City life is so up and moving and busy, I definitely am NOT a city person. I see people literally running all the time to get from A to B. Relax won’t you? geez.

anyways, until next time.

I know I said I would be posting hopefully about twice a week but you have to understand 3 simple things: 1. I am lazy 2. I am busy 3. All I want to talk about is how fucked up the system is and talk shit about it.

But instead, I will talk about what I did now that I FINALLY left my dorm room. As my mom know, because I call her to complain every day, I have had the most terrible allergies/ cold (???). I don’t know what kind of sick joke this is but it has got to stop !!

Anyways, we went to the Louvre Museum Friday night since people under 26 get in for free!

We only got to see about an hour worth the art before the museum closed.

There was art like this …

And of course the Mona Lisa:

I was not impressed at all by this painting. It also seemed like people were mostly just interested in taking pictures of it and not really viewing the art in front of them.

but my favorite was this piece:

It is called the Winged Victory of Samothrace. How do you manage to make stone look so fluid ???

Saturday I stayed in bed and drank lemon ginger tea all day.

Sunday, me and a couple of other students in the REU program went for lunch.

After lunch, we went to a museum called Musee et expositions or maybe even Center Pompudou. I am not entirely sure.

This museum was much more interesting than the Louvre.

But anyways, I am getting pretty tired. It is 12:00 am in Paris and I always take forever to write these blog post because I get distracted. So, goodnight or if you are my friends from California, good evening (???)

talk to you later alligators ! ( hehehe)

It’s been a while since you last heard from me, life has changed so drastically in the past week it is hard to even begin to explain it.

I have been doing research at Humboldt State University for about a year now. I just started doing research about 3/4 days ago at the Institut d’Optique graduate school. There is some MAJOR differences in the work environment.

I don’t want to say names, mostly because I didn’t ask anyone at the schoosl if it was okay to mention them so I want to respect their privacy.

Anyways, one of the woman I work with is Arabic and the other is Chinese. I LOVE working with them. This is so strange to me. In my regular HSU day, I feel like if I talk about personal things the staff ,faculty, and students just feel pity for me. I can actually have these conversation with my research group.

A regular work day consist of waking up around 7:00 am, walking over to the metro station around 8:00 am. I get to work around 9:00 am. around 10-11 we have a coffee break where we talk about anything we want.

If you know me, you know I love talking about equal access to education, racism, sexism, and basically anything that will cause tension.

Whenever I have these conversations with any faculty ( except one) at HSU I get bombarded with ” BUT WE HAVE THE HSI GRANT” ” WE HAVE STARS TO ROCKS” ” THE TUTORING HOURS GOT EXTENDED” ” WE ARE GIVING YOU THE BARE MINIMUM WHY ARE YOU COMPLAINING”

Okay, the last one is something I hear even if they don’t say it directly.

The point is that whenever I bring up anything that bothers me or directly affects me, people will try to tell me they are doing soooooo much. ( when really it is literally the bare freaking minimum).

It is so refreshing to talk about how schools lack support for students of color without being told they are doing the best. My advisor and grad student will listen, sympathies, and add on valuable information.

It feels so good to finally be able to speak my mind without being scared of the faculty or staff not liking me. Without feeling like i’m going to be told i’m crazy and emotional.

Every day I come in, read and learn about fiber optics and ask them questions about the topics i’m trying to learn. Not once have they told me ” YOU SHOULD KNOW THIS ALREADY” or ” THIS IS SO SIMPLE WHAT DON’T YOU UNDERSTAND”

They are so understanding and SUCH good teachers and mentors. I have learned so much in the past couple of days because it is so easy to ask for help. They do not belittle me. They do not make me feel stupid.

We also take a coffee break in the morning together, and we eat lunch together. My advisor is letting me borrow pots and pans so I can cook at my dorm. My grad student wrote me a list of places to visit and websites/stores to get discounts at. This is honestly something I would do for any person, but it is never reciprocated in Humboldt. I have realized that working with white men/women and having to be in spaces full of white male/women is so exhausting. Even more than I realized.

I am genuinely happy to go to work and to learn. I usually dread school in Humboldt. I don’t claim that everyone is terrible but it is so much easier when people around you understand how hard it is!

THIS IS WHY HSU NEEDS A MORE DIVERSE FACULTY. I will not keep quiet about this. They need to hire at least 2 faculty in the next couple of months and if they don’t realize that students of color need representation then they will hear a big roar from me. Anyways, this is just a short rant. I will be posting a blog about why I am not comfortable attending HSU and especially why I have problems with the physics/math department.