Prior to the terrorist attacks on Sept. 11, 2001, what technology was used at U.S. airports to detect explosives?

At 9-11, the only widespread technology that the U.S. airports had was old generation X-ray machines, plus gas chromatographs that relied on the analysis of solvent swabs. Explosives were difficult to detect and still are mainly because there are literally hundreds of different explosives that have been synthesized in the past and many widely different types of chemical compositions. Also, many common items, such as sugar, can be used to make explosives.

You handle explosives nearly every day. Do you have any problems when you fly?

I have only been stopped once and that was before 9-11. A bag I was carrying was accidentally contaminated with nitroglycerine by one of my graduate students. I take precautions not to be detected and have to constantly defeat the attempts of my students to contaminate me and get me caught -- the prospect of which they think is extremely amusing. I am impressed though by some of the new X-ray machines that use false color along with sophisticated image processing to scan luggage. On my last trip to Brazil, I brought back a large amethyst geode, which was identified on entering the United States in Miami without me even having to open my bag. That was very impressive.

How does the government plan to improve explosives detection?

There are a number of new breakthroughs in detecting explosives and their traces. For example, laser photoluminescence spectroscopy uses a laser to scan the surface of luggage and a sensor to detect light emissions from explosive contamination that are outside of the visible spectrum. Hopefully, for you reading this article, getting through an airport is going to be much quicker, simpler and safer in the future due to this and other high-tech gadgetry. Of course, it is just going to get more difficult for me.