14

Jan

Laser technique produces 3D models

May/June 2014 Volume 7 Issue 3

Ronald D Schaeffer - PhotoMachining

Ronald D. Schaeffer
CEO, PhotoMachining, Inc.
rschaeffer@photomachining.com

Laser ablation tomography (LAT) is a process that allows the structural features of organic and inorganic samples to be viewed as high-contrast, full-color, 3D models.

A LAT system developed at Penn State University incorporates a nanosecond, Q-switched, pulsed ultraviolet laser, a camera and Avizo 3D analysis software. During operation, thin, successive layers of a specimen are vaporized. Removal of the material only minimally affects the remainder of the specimen. A camera photographs the freshly ablated surface of the specimen after each laser pass. Data from the image is stored.

Laser ablation tomography can be used to create 3D models of organic samples, like this root. All images courtesy Lasers for Innovative Solutions.

When all the data is gathered, the software processes and reconstructs a high-resolution 3D model of the specimen’s interior and exterior that can be viewed, manipulated or virtually dissected.

A typical LAT setup is shown in Figure 1 (below). Samples are affixed to a cantilever, which connects to the travel axis of the laser’s mechanical stage. Slice thickness is determined by incrementing a linear stage after each exposure. Resolution as fine as 1µm at 18 million voxels per slice is possible, providing a detailed image based on the data captured during the process. Data tables are created automatically and are immediately available for analysis (see table below).

The LAT technique was invented by Benjamin Hall, a former student at Penn State and the co-author of this column; Dr. Jonathan Lynch, professor of plant nutrition at Penn State College of Agricultural Sciences; and Dr. Edward Reutzel, head of the Laser System Engineering and Integration Department at Penn State’s Applied Research Laboratory.

Hall and a business partner, former Penn State graduate student Brian Reinhardt, have licensed the technology and founded a company called Lasers for Innovative Solutions LLC (LIS) to commercialize it. Prospective customers include companies involved in agricultural and horticultural research.

LAT vs. other approaches

Technologies such as X-ray and magnetic resonance imaging (MRI) have traditionally been used to obtain tomography data. They have distinct disadvantages. For example, they often require complex sample preparation, which frequently includes the use of heavy-metal contrasting agents and stains. These techniques often are affected by the sample’s moisture content, density and composition.

Figure 1: The LAT system consists of a laser, galvanometer, scanner, camera and table.

The LAT process, on the other hand, requires virtually no sample preparation. The UV laser induces material-specific fluorescence, which facilitates detailed analysis because the fluorescent properties identify and discriminate among material structures at a level not possible by other means. Slices just a few hundred nanometers thick can be removed from a specimen, and the laser leaves a nearly parallel face on the sample. The result is higher-resolution images than when using other processes to characterize biological samples, such as standard microtome sectioning (processes for slicing thin sections from specimens). LAT scans are also several orders of magnitude faster than microtome sectioning.

Figure 2 depicts a maize root captured with X-ray microtomography and a LAT scan. In the LAT scan, the fluoresced orange sections correspond to components with high lignin content, while the blue/white sections represent those with high cellulose content.

Figure 2: Comparison of a maize root captured with (left) X-ray microtomography and an LAT scan (right).

The LAT technique can be used to generate 3D models of things other than plants.

Lasers for Innovative Solutions is developing LAT technology to characterize the structure and composition of rock samples, such as shale, that are of interest to the oil and gas industry. LAT scans also could be used for MEMS-device and biomedical applications.

One drawback to LAT is that it’s a destructive analytical technique, limiting its use to certain applications. However, for many applications, this is not an issue.

Root area

Root perimeter

Stele area

Stele perimeter

Aerenchyma area

Number of cortical cells

Average cortical cell area

Average xylem area

1.63

5.57

0.30

2.27

0.32

308.00

0.000948

0.0129

1.63

5.57

0.30

2.35

0.36

300.00

0.000929

0.0114

1.46

7.76

0.29

2.31

0.25

273.00

0.000895

0.0105

1.64

5.47

0.30

2.29

0.33

317.00

0.000894

0.0130

1.63

5.65

0.30

2.28

0.35

315.00

0.000883

0.0107

1.64

5.56

0.31

2.30

0.37

322.00

0.000884

0.0108

1.63

5.60

0.31

2.30

0.37

333.00

0.000882

0.0110

1.63

5.61

0.30

2.36

0.35

330.00

0.000903

0.0109

1.62

5.63

0.31

2.26

0.36

319.00

0.000925

0.0107

The LAT software automatically generates tables that compare different samples. Measurements are in millimeters.

On the horizon

All of the work performed by LIS so far has been done with a 355nm, nanosecond laser, but other lasers could be used to expand the power and utility of the technique. Potential candidates include shorter-wavelength (266nm) and shorter-pulse-length lasers, such as picosecond and femtosecond ones.

Though currently limited to examining samples, a more exciting prospect is to use the LAT technology to manufacture parts. Since digital information is created when performing LAT scans, the data could be transferred to a 3D printer to reconstruct the sample. This would allow the technology to be used to produce medical implants. µ

Editor's Note: Benjamin Hall, a founder of Lasers for Innovative Solutions, State College, Pa., contributed to this report. Web: http://l4is.com/.

Ronald D. Schaeffer, Ph.D., is CEO of PhotoMachining Inc., a high-precision laser job shop and systems integrator in Pelham, N.H. Telephone: (603) 882-9944. E-mail:  rschaeffer@photomachining.com | Laser MicroMachining at www.photomachining.com.

— R. Schaeffer