How Lasers Actually Work

I’ve been digging lately, looking for the next thing to wow my photon brain…  there’s been some LED developments and some other manufacturing-based tech dev that has been cool, but when you see something that peaks your curiosity, you’ve often got to go way back to the starting line and stretch.

Here’s some mind stretch for the photonics world — How Lasers Actually Work:


This article is from one of my favorite blogs, Hackaday.  It’s in your face.

From Wikipedia --

From Wikipedia —

And that is a big-ass Carbon Dioxide laser lasing and igniting a target.  Boom.

You know what blows my mind about lasers?  It’s just light.

This plywood is being cut by light.

This metal pipe and stuff?  Light.

Allllll light.

This is also all light:


Some companies and websites to check out:

X-Laser, who makes pretty bad ass laser packages for our industry
Pangolin, they make some interesting laser control software/hardware
Showlasers, a Dallas company that does some pretty amazing stuff
Edmund Optics, just get on their catalog list, they have the coolest freaking optics catalogs
Schaum’s Guide to Optics, probably one of the best optics books I’ve read
Real Genius, with Val Kilmer, one of the best nerd movies of all time, about lasers

Laser Goofing, JimOnLight Style

I was a fairly big laser nerd before I met Rick Hutton, but after becoming friends with THAT mega-nerd, I have begun to really get into lasers and the whole use of coherent light.  I think one of the highlights of 2011 so far was hitting Photonics West with Ocean Optics and SeaChanger and walking the laser show floor with Rick.  You see, I see the term mega-nerd as about the best compliment you could give a person.

I have been goofing a bit with my 1W blue (445nm), my 10mW HeNe (632.8nm), and a Coherent Radius 405 (violet, 405nm) I picked up pretty cheap on eBay.  I also have a ton of amazing optics and bench components that I was given by the great folks at InLight Gobos and Laser Surplus Sales.  I want to make some fun art with the stuff that I have, and as I acquire more, and one of these days I’ll save up and get a 5W Argon laser (oh HELL yes) and I’ll build some crazy system of galvos and any other crackadelic thing I can come up with to occupy my non-working, non-sleeping time.

I can’t afford the several thousand dollars for a decent laser breadboard for my hobby, so I pulled a DIY and built my own out of two chunks of fine-grade pine that I glued together and fastened with a few large gauge fasteners.  It cost me about 40 bucks total, which is a lot less than $1977.74, let me tell you.  I have about a 16th of an inch deflection over the course of the surface of the table, a grid of holes drilled on one inch centers over a 24″ x 60″.

Just a few teaser shots – I’m oretty bummed at the loss of my DSLR, my little 12MP Elph just ain’t cutting it with this specific wavelength photography:


Holy sh*t I love lasers. Wear your laser safety glasses, kids!

Rotary Photon Drag Enhanced by a Slow-Light Medium. Right? Right.

Remember that scene in the Jody Foster movie called Contact when they got all of those drawings of “the machine?”  There was a part of the movie where Ellie realized that the images were encoded somehow, and the key to encoding them was by looking at them in three dimensions.  Remember that minute little detail?

I read an article on this just the other day, and after I read the entire article in the journal Science, I really want to share the gist of this thing with you all.  It totally reminds me of this for some reason.  I was explaining this all to a friend on Skype, and I got tired of typing, and then the researcher slice of my brain started going ape-sh**.  Pardon me.

First, read the abstract of the article written by Sonja Franke-Arnold (School of Physics and Astronomy (SUPA), University of Glasgow, Scotland), Graham Gibson and Robert W. Boyd (Department of Physics, University of Ottawa, Ottawa, Canada), and Miles J. Padgett (The Institute of Optics and Department of Physics and Astronomy, University of Rochester, Rochester, NY):

Transmission through a spinning window slightly rotates the polarization of the light, typically by a microradian. It has been predicted that the same mechanism should also rotate an image. Because this rotary photon drag has a contribution that is inversely proportional to the group velocity, the image rotation is expected to increase in a slow-light medium. Using a ruby window under conditions for coherent population oscillations, we induced an effective group index of about 1 million. The resulting rotation angle was large enough to be observed by the eye. This result shows that rotary photon drag applies to images as well as polarization. The possibility of switching between different rotation states may offer new opportunities for controlled image coding.

Ok, got it?  Yeah, read it a few times, but generally the concept of the experiment is pretty simple, and the results are very interesting!  What these folks were doing was shining a shaped, collimated beam of light through a spinning ruby disk rotating at a given speed – in this case a maximum of 30 cycles per second.  The ruby disk causes a bit of “drag” on the photons travelling through it, causing the light to refract and exhibit some interesting behavior.  Check out this little video, from the paper and from the journal Science:

to view the .MOV file, click here

Ruby has a heavy Index of Refraction, which means the light is slowed down (refracted) at a rate of X when it leaves the air and enters the ruby itself.  If you imagine the 1.0 value of the Index of Refraction as how light travels through regular ol’ air (and not taking into account humidity, pollution, or any of that schtuff), anything greater than 1.0 is refracting.  Diamond has an Index of Refraction of about 2.42, and Ruby’s Index of Refraction is about 1.77.  Ruby refracts less than diamond.  Make sense if you didn’t already get it?

Here’s the weird thing – Ruby is not what we consider isotropic – meaning that no matter what the incidence angle is and no matter what the orientation of the crystal is, the light travels through the crystalline matrix equally as it travels through the medium.  Glass, sodium chloride crystals, and a lot of polymers exhibit this kind of “perfect” structure.  Sodium chloride is basically a cubic structure, relatively perfectly bonded in a cube matrix.  Ruby, on the other hand, is an anisotropic crystalline structure, meaning that there are more than one axes that are different within the structure of the crystal matrix.

Here’s a good image of the difference between an isotropic and anisotropic crystal structure, optically, from Olympus America’s Microscopy Resource Center.  Figure A is a sodium chloride crystal, which is isotropic.  Figure B is a calcite crystal, which has calcium ions and carbonate ions in it.  Calcite is anisotropic.  Check it:

Ok – now if you think of a crystal structure with light shining through its matrix, and the light is going to pass through two different planes of refraction, essentially – what do you expect to happen to one beam of light as it enters the anisotropic crystal structure and slows down?

Who said it’s going to split into two beams?  (DJ Lemma, pout your hand down, I know you already know the answer!)  You’d be correct – the incident beam splits into two beams, each sort-of along that individual crystal plane.  Take a look at this image of a calcium carbonate crystal, and how it is creating a double image:

This phenomenon is called birefringence.  Deep breath – bi-re-frin-gence.  Ruby, the gem used in the experiment, is also an anisotropic crystal, and it exhibits traits of birefringence.

So, imagine taking that birefringent crystal disk, spinning it at a relatively high rate (30 Hz), and shining a very specific wavelength of light (ie, a laser), that is in a certain shape through the ruby disk as it spins.  A bunch of stuff was discovered with this experiment, all related to the image.  The generalities of the experiment, as I paraphrase, is that the group shone a very bright laser with a square-ish shape through the ruby disk, noted the position that the laser had ont he other side of the ruby disk after it was on the other side of the disk.  When you shine a shaped laser beam at 532 nanometers (green) through a spinning ruby disk (which is a very slow-light medium, slowing the light down to just a few tens of meters per second) spinning at a rate between not spinning and 30 rotations per second, the image refracts from about a third of a degree to about ten degrees as the ruby disk increases from slow revolutions per second to thirty revs per second.

What a crazy experiment, huh?  I needed a good dose of photonics and optics in my Thursday!

The ramifications of this experiment have to do with encoding images with extra data – if you can imagine an image that has more information in it depending on which way the image is spinning, that is some trippy Minority Report shizzyhizzle.  “Oh, you’ve stolen my image!  But since you don’t know which wavelength to use and at which speed to spin the image, you’ll never decode my super secret plans of world domination!!!

Yeah, I have a vivid imagination.

HUGE number of thanks:
the journal Science
the Index of Refraction of Ruby and Sapphire (actually a very cool fact doc, check it out!)

The Anti-Laser – Scientists Discover How to Cancel Out a Laser Beam

Whoa – a laser story that doesn’t involve someone mounting a man-killing laser on top of some kind of vehicle?!  SAY IT AIN’T SO!

Professor Douglas Stone and his team of Yale scientists have discovered a way to get material to nearly completely absorb laser light.  They’ve developed this thing – more of a material, really – called a CPA, or Coherent Perfect Absorber.  What it seems the team has done is to take the Law of Conservation of Energy and used it to their advantage.  Do we all remember the Law of Conservation of Energy?

Energy can not be created or destroyed – it can only change form.

So what the scientists have done here, in layman’s terms, is that they’ve figured out a way to get laser light to basically be absorbed into a medium by waiting until that laser light bounces around this little silicon chamber until its energy changes forms to heat energy.  Stone and his team used a silicon structure to basically take beams of laser light and capture them in this silicon medium until they change form to heat energy.  Right now his team says that they can capture 99.4% of the light through absorption, but their Coherent Perfect Absorber will potentially be able to capture 99.99% of the laser light shone into the CPA.

Why this is significant is that silicon is already being used in the semiconductor industry in computers – this new technology from Yale and Douglas Stone’s team has potentially many, many uses in computing – the hope is that they’ll be able to use these tech as a way to make microswitches and other types of computer components.  Hey, using light instead of electrons?  Awesome!

Very cool!

Thanks CTV, BBC, PopSci, and NewScientist!