From the Lab to the Marketplace Ten Years Later, Energy Efficient Technologies from Research at the Lawrence Berkeley National Laboratory Berkeley Lab logo (left) with six rows of gray dots transitioning to a line art drawing of a cityscape and residential houses.

Laser Ablation Technology for Chemical Analysis

Analyzing materials to determine their chemical composition is a basic tool of science, and it is used everyday not just for pure research, but in such practical pursuits as food safety testing, explosives detection, and hazardous waste analysis and remediation.

However, the process of analyzing solid materials can itself result in hazardous waste, since these materials often need to be dissolved to form a liquid that can then be analyzed with a spectrophotometer.

A phenomenon known as laser ablation has led to development of a green technology for analyzing the composition of unknown solids, thanks to years of research by scientists at the Environmental Energy Technologies Division of the Lawrence Berkeley National Laboratory.

(1) Laser pulse is applied; (2) Induced plasma plume expands into the anbient gas; (3) particle formation occurs from solid-sample exfoliation; (4) Condensation occurs.

At the start of the laser pulse until one nanosecond later, violent evaporation takes place at the material's surface. From one nanosecond to one microsecond (1,000 ns) after the end of the pulse, the high-temperature plume expands outward. From one microsecond to 1,000 microseconds (1 millisecond) after the end of the pulse, the heat leaks away through radiative heating and the plume cools.

Left: plasma expands in 3-D; Right: plasma expands in 1-D, particles form due to condensation in plasma.

Laser ablation is the process of aiming a laser beam at the material sample to be tested, causing a tiny amount of it to be vaporized so that spectroscopic analysis techniques and unique computer software can analyze the sample in seconds. The technology reduces chemical waste from the testing process to essentially zero, simplifies the collection of samples, and speeds up the entire process immensely

After nearly 30 years of study, laser ablation has become the basis of a new chemical analysis technology. The two most common approaches are LIBS, (laser induced breakdown spectroscopy) in which the light from a tiny plasma is directly measured and related to the chemical element and its concentration, and LA-ICP-MS (laser ablation inductively coupled plasma mass spectrometry), in which tiny particles from the ablation are measured. On average, LIBS provides part-per-million sensitivity whereas LA-ICP-MS provides parts-per-billion sensitivity. Both approaches allow the measurement of the entire chemical composition of a sample target using a single laser pulse.

Laser ablation optical and mass spectrometry with inductively coupled plasma schematic.

In laser induced breakdown spectroscopy, the plasma emission from the ablated sample is gathered using special optics. A spectrometer analyzes the white light emitted from the plasma, separating the light into its colors (wavelengths).

Screenshot of the Laser Spectroscopy and Applied Materials Group web site. Applied Spectra logo

Rick Russo, who leads the Laser Spectroscopy and Applied Materials Group in the Environmental Energy Technologies Division, began studying the physics of laser ablation in the early 1980s. In 2004, he created a company, with the help of Small Business Innovation Research grants, called Applied Spectra to bring the technology, and its many potential life-saving applications, to the marketplace. It sold its first LIBS device in 2008. The company's corporate offices are in Fremont, California, a community 30 miles south of Berkeley, in the eastern part of Silicon Valley. It also has a small manufacturing facility in Aberdeen, Maryland. The jobs created by the company are "green" jobs, since the technology is a waste reducing one.

Most of the samples in the world that chemists want to analyze are solid. The conventional method of analysis requires an entire analysis infrastructure that is based on dissolving these solids in strong acid so that the resulting liquid can be analyzed using standard methods. This is very dirty, generates a lot of chemical waste, and requires a lot of labor and time.

In contrast, laser ablation requires no acid dissolution and so generates no hazardous wastes. Laser ablation is green technology. Besides eliminating chemical waste, it saves energy. Laser ablation is also very fast, allowing technicians to conduct more tests on samples in real time. And, laser ablation testing is cheaper—only a technician is needed to operate the tool. The technician's job is to place the sample and operate the machine; each test takes less than 30 seconds. No PhDs are needed.

Laser ablation-based explosives detection system at the Yuma Proving grounds.

Tests of a military prototype field version of the laser ablation-based explosives detection system at the Yuma Proving grounds in 2008.

The basic research has been funded for many years by the U.S. Department of Energy's Office of Basic Energy Science. But the application research for laser ablation has been funded by many other offices, such as the Nuclear Non-Proliferation and Security Agency of DOE, which was interested in laser ablation's potential for quick identification of nuclear wastes at nuclear manufacturing sites, and the Department of Defense, which was looking for ways to remotely and quickly identify explosive residues that might provide tell-tale hints of car bombs and other terrorist weapons.

Russo and his co-workers tested a military prototype field version of the LIBS system at the Yuma Proving grounds in 2008. The detector was able to discriminate with 85 percent accuracy whether more than 100 samples contained residues of several types of explosives from between 30 to 50 meters (90 to 150 feet) away, or whether the composition was of materials such as rock, wood, metal, plastics or, in one case, food materials—salami and cheese.

Applied Spectra has developed several commercial versions of this tool, and is planning to release a hand-held, and transportable version later in 2009.

Detecting Lead and Other Heavy Metals

Clockwise from top: RoHS logo, three painted toys, Waste Electrical and Electronic Equipment

With so many news stories recently about imported toys and other products painted or otherwise contaminated by lead, testing labs and consumer safety authorities need faster, accurate ways of determining which products to be concerned about.

Many European and Asian nations have adopted regulations requiring the removal of hazardous materials from new and to-be-recycled electronic components called Restrictions on Hazardous Substances (RoHS) and Waste Electrical and Electronic Equipment (WEEE). More stringent U.S. regulations are also being looked at. Lead, cadmium, mercury, hexavalent chromium, and organic materials PBB and PBDE are among the dangerous materials that these regulations are aiming to remove from the products we use every day. Research has demonstrated that LIBS testing is more accurate than today's X-ray fluorescence technology for quick screening of these materials.

Laser ablation-based testing can also be used in a variety of other "green" and "green policing" applications. For example, one manufacturer of electronic components is using it to check on the soldering of electronic components to ensure that they are free of lead, which many countries now require. It can also analyze the purity of silicon used in solar photovoltaic panels for quality control.

Assisting with Detection of Wastes at Contaminated Sites

Left: Abandoned mine in the desert; Right: Yellow barrels of nuclear waste.

Those performing the clean-up of old mining sites will find LIBS technology useful in identifying the contaminants at the sites, information that can guide waste management experts determining the best methods to use to clean up and isolate what's present.

Some of the research also has been oriented toward using LA to detect residues of nuclear weapons development for use in nuclear non-proliferation programs.

The development of laser ablation serves as an example of fundamental research to better understand a natural phenomenon that led to an unexpected, but useful application in the industrial and commercial world.

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