Randomly arranged items usually have poor optical properties. The rough—or random—surface of a frosted-glass window, for example, obscures the view of an object.
Computed optical light fields in a random laser overlaid on black circles, which represent the nanoholes drilled into a semiconductor quantum cascade laser, to produce a laser pattern with low spatial coherence.
© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
The optical industry therefore expends considerable effort reducing any surface irregularities in optical devices to avoid the uncontrollable scattering of light characteristic of random structures.
But now, a research group led by Ying Zhang from the A*STAR Singapore Institute of Manufacturing Technology (SIMTech) has made good use of randomness by studying how random structures can improve the performance of lasers. Together with a team led by Qijie Wang at Nanyang Technical University in Singapore, the group has demonstrated the world’s first electrically pumped mid-infrared random laser, which operates at a 10-micrometer wavelength. The laser is as bright as conventional diode lasers but produces less-speckled images.
Light waves from a conventional laser oscillate in perfect synchronicity, across both time and space. Perfect alignment of the light waves at different time and different locations across the beam profile is known as temporal and spatial coherence, respectively. When a laser illuminates a surface, a speckled pattern is typically visible, which indicates spatial coherence. The speckles result from the laser beam reflecting from different parts of the surface. Because the waves are in sync, they create spatial interference effects in the eye of an observer. This distortion is undesirable, particularly in biomedical imaging applications conducted in the infrared region of the spectrum.
Random lasers are the solution to this type of distortion, says Zhang. “Random lasers show the same high temporal coherence as that of other lasers but have a lower spatial coherence,” he explains. “High temporal coherence gives the desirable brightness but it is the low spatial coherence that removes the speckles caused by interferences.”
To realize a random laser in the mid-infrared spectrum, Zhang and co-workers used a semiconductor quantum cascade laser into which they had drilled a random pattern of nanoholes. At a sufficiently high density, these holes prevent the formation of a regular laser pattern within the semiconductor (see image). Instead, the pattern of a random laser forms, with low spatial coherence.
Employing a quantum cascade laser to realize the random lasers allows for the polarization of the laser light perpendicular to the laser surface. This propagation minimizes losses owing to the air-hole structure.
The research team’s wafer-fabrication competencies enabled them to drill holes deep enough into the laser chip, with sufficiently smooth side walls to minimize losses in the laser itself. By introducing these perfections and overcoming a number of other practical hurdles, Zhang and his colleagues succeeded in making the lasers efficient enough to provide lasing during electrical operation.
Nevertheless, notes Hou Kun Liang of SIMTech, who invented the mid-infrared random laser, more work is needed to bring random lasers to market. “We are working on a random laser that operates at room temperature. And in the long-term, we plan to extend random lasers from the infrared to even longer wavelengths and can be used for inspection of various polymer packaging quality-control of printed electronics, biomedical imaging, among other applications.”
About the Singapore Institute of Manufacturing Technology
The A*STAR Singapore Institute of Manufacturing Technology (SIMTech) develops high-value manufacturing technology and human capital to contribute to the competitiveness of Singapore’s industry. It collaborates with universities as well as multinational and local companies in the precision engineering, electronics, semiconductor, medical technology, aerospace, automotive, marine, logistics and other sectors.
Liang, H. K., Meng, B., Liang, G., Tao, J., Chong, Y., Wang, Q. J. & Zhang, Y. Electrically pumped mid-infrared random lasers. Advanced Materials 25, 6859—6863 (2013).
A*STAR Research | Research asia research news
Etching Microstructures with Lasers
25.10.2016 | Fraunhofer-Institut für Lasertechnik ILT
Applying electron beams to 3-D objects
23.09.2016 | Fraunhofer-Institut für Organische Elektronik, Elektronenstrahl- und Plasmatechnik FEP
In recent years, lasers with ultrashort pulses (USP) down to the femtosecond range have become established on an industrial scale. They could advance some applications with the much-lauded “cold ablation” – if that meant they would then achieve more throughput. A new generation of process engineering that will address this issue in particular will be discussed at the “4th UKP Workshop – Ultrafast Laser Technology” in April 2017.
Even back in the 1990s, scientists were comparing materials processing with nanosecond, picosecond and femtosesecond pulses. The result was surprising:...
Have you ever wondered how you see the world? Vision is about photons of light, which are packets of energy, interacting with the atoms or molecules in what...
A multi-institutional research collaboration has created a novel approach for fabricating three-dimensional micro-optics through the shape-defined formation of porous silicon (PSi), with broad impacts in integrated optoelectronics, imaging, and photovoltaics.
Working with colleagues at Stanford and The Dow Chemical Company, researchers at the University of Illinois at Urbana-Champaign fabricated 3-D birefringent...
In experiments with magnetic atoms conducted at extremely low temperatures, scientists have demonstrated a unique phase of matter: The atoms form a new type of quantum liquid or quantum droplet state. These so called quantum droplets may preserve their form in absence of external confinement because of quantum effects. The joint team of experimental physicists from Innsbruck and theoretical physicists from Hannover report on their findings in the journal Physical Review X.
“Our Quantum droplets are in the gas phase but they still drop like a rock,” explains experimental physicist Francesca Ferlaino when talking about the...
The Max Planck Institute for Physics (MPP) is opening up a new research field. A workshop from November 21 - 22, 2016 will mark the start of activities for an innovative axion experiment. Axions are still only purely hypothetical particles. Their detection could solve two fundamental problems in particle physics: What dark matter consists of and why it has not yet been possible to directly observe a CP violation for the strong interaction.
The “MADMAX” project is the MPP’s commitment to axion research. Axions are so far only a theoretical prediction and are difficult to detect: on the one hand,...
16.11.2016 | Event News
01.11.2016 | Event News
14.10.2016 | Event News
07.12.2016 | Health and Medicine
07.12.2016 | Life Sciences
07.12.2016 | Health and Medicine