Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Advances in lasers get to the long and short of it

25.01.2018

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.


This is a demonstration of CLC lasing device with liquid crystals self-assembled into helices.

Credit: Chun-Ta Wang

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.

In addition to tuning the lasing wavelength, one hot area of inquiry is in finding different ways of tuning the wavelength by switching the lasing mode from one edge of the photonic bandgap to the other. Some attempts so far have suggested it is possible to switch between the long- and short-wavelength edges.

Wang's team's work demonstrates that this mode switching is possible by applying a direct-current electric field to the fluorescent dye, altering its order parameter without affecting the spectral position of its bandgap. The researchers tested three mixtures by varying ratios of liquid crystals and dyes and recording their laser outputs through fiber-optic spectrometry.

They found that it was possible for all the samples to shift from lasing at the short-wavelength edge to lasing at the long-wavelength edge, a shift of nearly 40 nanometers, with as little as 20 volts. Moreover, a polymer-stabilized planar CLC sample was able to leverage its extra structural stability to reversibly switch between the two modes and showed improved performance and threshold voltage.

"There have been many calculations for how to achieve this phenomenon in this field, but to our knowledge, this is the first time it was proven experimentally," Wang said.

Looking ahead, Wang said widespread use of CLC lasers is still slated for the future. In the meantime, he and his team are hoping to expand our understanding of electrically assisted band-edge mode selection in other types of photonic crystals.

###

The article, "Electrically assisted bandedge mode selection of photonic crystal lasing in chiral nematic liquid crystals," is authored by Chun-Ta Wang, Chun-Wei Chen, Tzu-Hsuan Yang, Inge Nys, Cheng-Chang Li, Tsung-Hsien Lin, Kristiaan Neyts and Jeroen Beeckman. The article appeared in Applied Physics Letters Jan. 22, 2018 (DOI: 10.1063/1.5010880) and can be accessed at http://aip.scitation.org/doi/full/10.1063/1.5010880.

ABOUT THE JOURNAL

Applied Physics Letters features concise, rapid reports on significant new findings in applied physics. The journal covers new experimental and theoretical research on applications of physics phenomena related to all branches of science, engineering, and modern technology. See http://apl.aip.org.

Media Contact

Julia Majors
media@aip.org
301-209-3090

 @AIPPhysicsNews

http://www.aip.org 

Julia Majors | EurekAlert!

More articles from Physics and Astronomy:

nachricht UNH scientists help provide first-ever views of elusive energy explosion
16.11.2018 | University of New Hampshire

nachricht NASA keeps watch over space explosions
16.11.2018 | NASA/Goddard Space Flight Center

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: UNH scientists help provide first-ever views of elusive energy explosion

Researchers at the University of New Hampshire have captured a difficult-to-view singular event involving "magnetic reconnection"--the process by which sparse particles and energy around Earth collide producing a quick but mighty explosion--in the Earth's magnetotail, the magnetic environment that trails behind the planet.

Magnetic reconnection has remained a bit of a mystery to scientists. They know it exists and have documented the effects that the energy explosions can...

Im Focus: A Chip with Blood Vessels

Biochips have been developed at TU Wien (Vienna), on which tissue can be produced and examined. This allows supplying the tissue with different substances in a very controlled way.

Cultivating human cells in the Petri dish is not a big challenge today. Producing artificial tissue, however, permeated by fine blood vessels, is a much more...

Im Focus: A Leap Into Quantum Technology

Faster and secure data communication: This is the goal of a new joint project involving physicists from the University of Würzburg. The German Federal Ministry of Education and Research funds the project with 14.8 million euro.

In our digital world data security and secure communication are becoming more and more important. Quantum communication is a promising approach to achieve...

Im Focus: Research icebreaker Polarstern begins the Antarctic season

What does it look like below the ice shelf of the calved massive iceberg A68?

On Saturday, 10 November 2018, the research icebreaker Polarstern will leave its homeport of Bremerhaven, bound for Cape Town, South Africa.

Im Focus: Penn engineers develop ultrathin, ultralight 'nanocardboard'

When choosing materials to make something, trade-offs need to be made between a host of properties, such as thickness, stiffness and weight. Depending on the application in question, finding just the right balance is the difference between success and failure

Now, a team of Penn Engineers has demonstrated a new material they call "nanocardboard," an ultrathin equivalent of corrugated paper cardboard. A square...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

Optical Coherence Tomography: German-Japanese Research Alliance hosted Medical Imaging Conference

19.11.2018 | Event News

“3rd Conference on Laser Polishing – LaP 2018” Attracts International Experts and Users

09.11.2018 | Event News

On the brain’s ability to find the right direction

06.11.2018 | Event News

 
Latest News

New materials: Growing polymer pelts

19.11.2018 | Materials Sciences

Earthquake researchers finalists for supercomputing prize

19.11.2018 | Information Technology

Controlling organ growth with light

19.11.2018 | Life Sciences

VideoLinks
Science & Research
Overview of more VideoLinks >>>