A new way of modifying the dipole moment of cholesteric liquid crystals allows for researchers to select between the different band-edge modes experimentally for the first time.
Since lasers were first developed, the demand for more adaptable lasers has only increased. Chiral nematic liquid crystals (CLCs) are an emerging class of lasing devices that are poised to shape how lasers are used in the future because of their low thresholds, ease of fabrication, and ability to be tuned across wider swaths of the electromagnetic spectrum. New work on how to select band-edge modes in these devices, which determine the lasing energy, may shine light on how lasers of the future will be tuned.
The laser cavities are formed of a chiral nematic liquid crystal doped with a fluorescent dye. The liquid crystal creates a photonic bandgap in the laser cavity. An international team of researchers demonstrated a technique that allows the laser to electrically switch emission between the long- and short-wavelength edges of the photonic bandgap simply by applying a voltage of 20 V. They report their work this week in Applied Physics Letters, from AIP Publishing.
"Our contribution is to find a way to change the orientation of the transition dipole moment of the gain medium [the fluorescent dye] in the CLC structure and achieve mode selection between long- and short-wavelength edges without tuning the position of the photonic bandgap," said Chun-Ta Wang, an author of the paper. "We also demonstrated a polymer-stabilized CLC system, which improved the laser's stability, lasing performance and threshold voltage."
CLC lasers work through a collection of liquid crystals that self-assemble into helix-shaped patterns, which then act as the laser's cavity. These helices are chiral, meaning they corkscrew in the same direction, which allows them to be tuned across a wide range of wavelengths. While many lasers, like the laser diodes used in DVD players, are fixed at one color, many CLC lasers can be tuned to multiple colors in the visible light spectrum and beyond.
Chun-Ta Wang, Chun-Wei Chen, Tzu-Hsuan Yang, Inge Nys, Cheng-Chang Li, Tsung-Hsien Lin, Kristiaan Neyts and Jeroen Beeckman. Electrically assisted bandedge mode selection of photonic crystal lasing in chiral nematic liquid crystals. Applied Physics Letters Jan. 22, 2018 (DOI: 10.1063/1.5010880.
(Score: 4, Funny) by The Mighty Buzzard on Tuesday January 30 2018, @03:30AM
I could see an immediate use for this in the shark-mounted laser field. Shorter wavelengths carry more energy at a lower amplitude in clear water but have less ability to penetrate murky water without significant energy loss. The ability to switch on the fly, possibly even in an automated manner based on environmental conditions, would definitely save some annoyance.
My rights don't end where your fear begins.
(Score: 0) by Anonymous Coward on Tuesday January 30 2018, @05:41AM (1 child)
Looks like the whole Wu-Tang clan was in on that shit...
(Score: 3, Informative) by c0lo on Tuesday January 30 2018, @01:56PM
It is called: "The times when US scientific progress come mainly from Wu-Tang Clan et al".
Gotta get use to it, can't have the 'teach the controversy' then, some years later, expect major scientific progress to come from the "controverted" people.
https://www.youtube.com/watch?v=aoFiw2jMy-0 https://soylentnews.org/~MichaelDavidCrawford
(Score: 2) by FatPhil on Tuesday January 30 2018, @09:17AM (1 child)
Errr... why?
I looked up "chiral" in the dictionary to see if it said anything apart from "posessing handedness", and it didn't mention anything to do with "able to tune lasers to different frequencies when used as the cavity medium".
Great minds discuss ideas; average minds discuss events; small minds discuss people; the smallest discuss themselves
(Score: 1, Informative) by Anonymous Coward on Tuesday January 30 2018, @03:15PM
Here is the first part from the paper's introduction section:
As you can see, the helical pitch factors into the width of the bandgap, and hence the wavelengths emitted (since they depend upon the bandgap edges), so a useful way to tune the wavelengths you want is to change the helical pitch (or, how tightly the helixes are wound). The paper mentions that one can do this using electric fields, heat, light, and mechanical stress.
You can get lasing from either edge of the bandgap, and what this particular paper is about is how you can pick which edge of the bandgap you want to use, as well as to switch between them.
(Score: 2) by ilsa on Tuesday January 30 2018, @10:24PM
I see that you are using words. I too like to use words. I use all kinds of words. It's so much fun to use words that sound like language, but when put together, remind you of that "Chicken Chicken Chicken" paper.
The look on the face of the receiving person is priceless.