Category: laser

LIGO’s Lasers Can See Gravitational Waves, Even Though The Waves Stretch The Light Itself

“But this is where the puzzle comes in: if space itself is what’s expanding or compressing, then shouldn’t the light moving through the detectors be expanding or compressing too? And if that’s the case, shouldn’t the light travel the same number of wavelengths through the detector as it would have if the gravitational wave had never existed?

This seems like a real problem. Light is a wave, and what defines any individual photon is its frequency, which in turn defines both its wavelength (in a vacuum) and its energy. Light redshifts or blueshifts as the space it’s occupying stretches (for red) or contracts (for blue), but once the wave has finished passing through, the light returns to the same wavelength it was back when space was restored to its original state.

It seems as though light should produce the same interference pattern, regardless of gravitational waves.”

Have you ever thought about how gravitational wave detectors work? By passing light down two mutually perpendicular arms, reflecting them back and reconstructing an interference pattern, we can detect a passing wave by how it changes the arm-lengths of the light. But the light itself also gets compressed and expanded, and shouldn’t those effects cancel out?

Clearly, LIGO, Virgo and KAGRA all work, as many detected events bear out. But have you ever thought about how? Come get the answer today!

A couple of weeks ago, we discussed about the famous Photograph-51 and how
that led to the discovery of the Double Helix structure of DNA.

mentioned in that post that the best way to visualize that diffraction
pattern is by using a laser and pointing it on a helix from a ballpoint


And in the previous post on pixels, we learned about how the RGB pixels arranged on a screen come together to render those beautiful images on your screen.


                                        Source : Microworld

The pixel arrangement on a screen need not be periodic like shown above. In fact ,most manufacturers have their own unique type of representation ( see below )and the type varies with the type of application as well.


As an amateur physicist you do not have a microscope but only a green laser as your tool, how would you go about finding which one of these arrangement your smartphone has ?

Visualizing pixel spacing using a LASER

For a fact, you know that:

if you shine a red light on a green or blue object, it will
appear black.



So if you take your green laser pointer and shine it on any of those pixel blocks, you know that you are only going to get green light from the green filter.


The other two filters will absorb the green light.

And using that you can find out the type of pixel arrangement your smartphone has.

We will be testing it out with Samsung Galaxy S4 whose  pixel arrangement on the screen looks like so:


Notice the oval nature of the green dots.

Let’s shine a green laser on the screen observe the resulting diffraction  pattern:


The diffraction pattern that you obtain is the following:


Observe that the dots on the image are not circles but ovals instead. This is due to the nature of the pixel arrangement on the Galaxy S4.

If you had a good red laser (which we did not) and tried this same experiment, you would get a pattern like so:


You are also welcome to try it on a smartphone of your choice or any electronic display and compare it with the pixel arrangement of that particular device.


This paper (from which the above image has been taken) runs through some more examples of the diffraction pattern that one obtains from common electronic components.

Have fun!

Related Interesting videos:

LCD Technology: How it Works

How a TV Works in Slow Motion – The Slow Mo Guys

* As with any diffraction pattern, you can measure the distance between the two dots and calculate the distance between two consequent pixels using the wavelength of the light source as given.

Interference pattern using Human hair and LASER pointer

Accidentally I put my messed up hair in between a laser pointer  and observed these beautiful Interference patterns.

Nice to know that interference is so easy to set up. Absolutely fascinating..

Ask Ethan: Can A Laser Really Rip Apart Empty Space?

“Science Magazine recently reported that Chinese physicists will start building a 100-petawatt(!!!) laser this year. Can you please explain how they plan to achieve this, and what unique phenomenon this will help physicists explore? Such as, what exactly is “breaking the vacuum?"”

As we strive for the greatest frontiers in physics, that always means pushing the limits. To that extra digit closer to absolute zero, the extra factor in high energy particles, the extra depth into the distant Universe. Or, in the case of laser physics, to that extra intensity: power focused into an extremely narrow space. There are three things you need to up that to the maximum amount possible:

-the most extreme amount of energy,
-in the shortest-span of a pulse,
-focused on the narrowest area possible.

If you can make it all the way up to a high enough energy, you should be able to rip electron/positron pairs out of the quantum vacuum (empty space) itself. Colloquially, people have started calling this “breaking the quantum vacuum,” but in reality, nothing gets broken.

The scientific truth is far more interesting! Come get the full story on this edition of Ask Ethan!