By Chencheng Zhao

Smaller can be better.

A new laser developed by Northwestern University researchers can pack a lot of punch into a single thumbnail-sized chip.

Unlike a laser used for a laser pointer, the compact laser developed at Northwestern emits in the mid-infrared spectral region. One of the primary appeals of mid-infrared lasers is for chemical and biomedical spectroscopy. This technique is fast and accurate, but is often limited by the size and cost of mid-infrared laser systems, according to Manijeh Razeghi, professor of electrical engineering and computer science at McCormick School of Engineering, who led the study.

Razeghi and her team presented their findings in the Dec. 21 issue of Applied Physics Letters (High power continuous operation of a widely tunable quantum cascade laser with an integrated amplifier).

“One application of this kind of laser is to detect hazardous chemicals in an industrial environment. Rather than using many point sensors, a single tunable laser could monitor the entire site for a contaminant by continuous scanning of the area,” said Razeghi.

“In the mid-infrared, the laser power does not need to be very high to achieve this, so the method can also be eye-safe,” she added, speaking of the possibility of adopting the technology for on-site monitoring.

The new device incorporates an on-chip amplifier, enabling an enhanced tuning range and demonstrating an order of magnitude with higher output power than in the past. “A wide tuning range is desirable for detecting a large number of chemicals simultaneously. Higher output power leads to a stronger signal or longer range,” said Razeghi.

The higher output and the wider tuning range makes it possible to search for all types of hazardous chemicals, such as industrial pollution, explosives, or even chemical warfare agents.

Razeghi and her colleagues at the Center for Quantum Devices aim to push the limits of technology. “We take inspiration from nature by making devices that are compact, multifunctional, and power efficient, just like your eyes or brain,” said Razeghi. The single chip laser requires no external optics or motors for tuning, which makes them much smaller than competing technologies.

Razeghi and her colleagues at the Center for Quantum Devices aim to push the limits of technology. “We take inspiration from nature by making devices that are compact, multifunctional, and power efficient, just like your eyes or brain,” said Razeghi. The single chip laser requires no external optics or motors for tuning, making them much smaller than competing technologies.

“We are developing lasers which are smaller, more robust, and potentially lower cost,” said Razeghi. “I say ‘potentially’ because they are not yet for sale.”

A single component source leads to simple assembly and straightforward mass production.

“Costs on the order of $5,000 or less per laser are feasible, which will be a game changer for users of this technology,” said Razeghi. “Traditional systems can be several feet square, depending on the power level. Costs can range from $50,000-$100,000 for these systems.”

Semiconductor lasers play a significant role in many different applications, including optical communications, DVD players, printers, laser-based 3-D scanners, range finders, automatic tracking devices, and bar code readers.

Romanian researcher Dan Sporea praised the Northwestern researchers’ work. He said, “Most of the achievements in what we call today photonics are based on the tremendous tool we have — the laser.” heads the Laser Metrology and Standardization Laboratory, at the National Institute for Laser, Plasma and Radiation Physics in Magurele, Romania. Semiconductor lasers play a significant role in many different applications,

Sporea heads the Laser Metrology and Standardization Laboratory, at the National Institute for Laser, Plasma and Radiation Physics in Magurele, Romania.

Using mid-infrared laser diodes for spectroscopy is not a new idea. A special class of semiconductor lasers dedicated to spectroscopic applications in the mid-infrared range (3.5 μm to 12 μm) was reported 20 years ago, Sporea said. However, these lasers historically suffered from low power and narrow tuning, and they often required cryogenic cooling. The new single chip laser developed by Razeghi’s group has none of these shortcomings.

“Within this context, the newly reported achievement of professor Manijeh Razeghi …  on the design of single-mode operated, wide tuning and high output power represents an important contribution in promoting [quantum cascade laser] in standoff applications,” said Sporea, coordinator of several international and national research projects and co-author of several book chapters in the field.