Nav: Home

Changing the color of laser light on the femtosecond time scale

June 14, 2017

How can the color of laser light be changed? One popular method to achieve this is the so-called second harmonic generation (SHG) effect, which doubles the frequency of light and hence changes its color. However, observing this nonlinear effect requires a polar crystal in which inversion symmetry is broken. For this reason, identifying crystals that can elicit strong SHG has been an important research topic, so that their properties can be exploited for applications in materials science.

Observation of nonlinear optical phenomena like SHG requires a finite second-order electric susceptibility, which occurs within any polar structure without inversion symmetry, and strong laser light or pulses. In the perovskite-type cobalt oxide BiCoO3 used in this work, an apical oxygen shift along the c-axis and a Co-O5 pyramid are present in the unit cell, resulting in symmetry breaking and a large spontaneous polarization at room temperature. For the laser pulse, the strong electromagnetic wave with an electric field up to ~1 MV/cm in the THz energy region was developed by Hideki Hirori and his team at iCeMS and was used to achieve ultrafast control of BiCoO3's nonlinear behavior.

Yoichi Okimoto at Tokyo Institute of Technology and colleagues were specifically interested in understanding how the intensity of SHG from the BiCoO3 crystal changes when irradiated with a THz (i.e., far-infrared) laser pulse at room temperature. Notably, an unprecedented enhancement of SHG by more than 50 % was observed, indicating that employing THz laser light in this fashion can significantly improve the figure of merit of nonlinear crystals. In addition, this effect occurs on the 100 femtosecond (10-13 s) time scale, suggesting possible application to ultrafast optoelectronic devices.

Mechanistically, the ultrafast enhancement of the second harmonic signal can be understood in terms of d-d transitions from occupied to unoccupied states that exist around the wide energy band of the applied THz pulse. The photoexcited electrons elongate the apical oxygen atoms of the Co-O5 pyramids in the crystal structure via electron-phonon coupling, thereby augmenting its polar structure (and hence second-order electric susceptibility).

Future investigations of the photoexcited state of BiCoO3 and other polar oxide materials will consider higher-order nonlinear optical responses as well as ultrafast structural measurements using the THz pulse to elucidate additional mechanistic details of these fascinating materials.
-end-


Tokyo Institute of Technology

Related Laser Pulse Articles:

The sharpest laser in the world
With a linewidth of only 10 mHz, the laser that the researchers from the Physikalisch-Technische Bundesanstalt (PTB) have now developed together with US researchers from JILA, a joint institute of the National Institute of Standards and Technology and the University of Colorado Boulder, has established a new world record.
Biggest X-ray laser in the world generates its first laser light
European XFEL, the biggest X-ray laser in the world, has generated its first X-ray laser light.
Nutrition report calls for greater cooperation and coordination in promotion of pulse as consumer-friendly food stuff
The Special Issue of Annals addresses the opportunity pulses present to address global concerns on nutrition, health, and sustainability.
Researchers shoot for success with simulations of laser pulse-material interactions
University of Virginia professor Leonid Zhigilei led a team that used the Oak Ridge Leadership Computing Facility's Titan supercomputer to gain deeper insights into laser interactions with metal surfaces.
Researchers flip a magnetic memory cell with a light pulse at record speed
University of Minnesota electrical and computer engineering researchers have created a magnetic tunnel junction that can be switched by a pulse of light lasting one trillionth of a second -- a new record.
When ultrafast laser pulse meets magnetic materials
The ultrafast laser-excited magnetization dynamics of ferromagnetic La0.67Sr0.33MnO3 (LSMO) thin films with BiFeO3 (BFO) coating layers grown by laser molecular beam epitaxy are investigated using the optical pump-probe technique.
New record achieved in terahertz pulse generation
A group of scientists from TU Wien and ETH Zurich have succeeded in their attempts to generate ultrashort terahertz light pulses.
New 'needle-pulse' beam pattern packs a punch
A new beam pattern devised by University of Rochester researchers could bring unprecedented sharpness to ultrasound and radar images, burn precise holes in manufactured materials at a nano scale -- even etch new properties onto their surfaces.
Scientists measure pulse of CO2 emissions during spring thaw in the Arctic
Scientists at Lawrence Berkeley National Laboratory documented a spring pulse in northern Alaska in 2014 that included CO2 emissions equivalent to 46 percent of the net CO2 that is absorbed in the summer months and methane emissions that added 6 percent to summer fluxes.
Symposium promotes versatile, vital pulse crops
International Year of Pulses highlights the role of sustainable crops and nutritious foods.

Related Laser Pulse Reading:

Best Science Podcasts 2019

We have hand picked the best science podcasts for 2019. Sit back and enjoy new science podcasts updated daily from your favorite science news services and scientists.
Now Playing: TED Radio Hour

Changing The World
What does it take to change the world for the better? This hour, TED speakers explore ideas on activism—what motivates it, why it matters, and how each of us can make a difference. Guests include civil rights activist Ruby Sales, labor leader and civil rights activist Dolores Huerta, author Jeremy Heimans, "craftivist" Sarah Corbett, and designer and futurist Angela Oguntala.
Now Playing: Science for the People

#521 The Curious Life of Krill
Krill may be one of the most abundant forms of life on our planet... but it turns out we don't know that much about them. For a create that underpins a massive ocean ecosystem and lives in our oceans in massive numbers, they're surprisingly difficult to study. We sit down and shine some light on these underappreciated crustaceans with Stephen Nicol, Adjunct Professor at the University of Tasmania, Scientific Advisor to the Association of Responsible Krill Harvesting Companies, and author of the book "The Curious Life of Krill: A Conservation Story from the Bottom of the World".