Photonics Spectra

Although researchers have been focusing on sources, detectors have also been improving. One example comes from Teledyne Dalsa, the Waterloo, Ontario, Canada-based camera maker. In December 2010, the company announced a CMOS line-scan camera with 1146-megapixel-per-second throughput. The data rate is high enough that the camera requires a new interface. Dubbed HSLink, it forms the foundation for Camera Link HS, a proposed successor to the interface standard Camera Link.

Another example comes from Fairchild Imaging, a Milpitas, Calif.-based company – currently being acquired by British defense contractor BAE Systems – that makes both CMOS- and CCD-based imaging systems. The company realized a few years ago, said Colin Earle, vice president of sales and marketing for Fairchild Imaging, that the scientific community could use a faster, higher sensitivity sensor with more dynamic range than CCDs offer. The company therefore developed its scientific CMOS sensors. Fairchild Imaging partnered with both Andor Technology plc of Belfast, UK, and Kelheim, Germany-based PCO in bringing to market systems that are based on the technology.

Earle said that the sensors and imaging systems based on them have been well received. They offer capture rates of up to 100 fps, about five times faster than comparable CCD sensors, but do so without sacrificing what’s important to the target market.

In particular, researchers want a low-noise sensor, Earle said. “A scientist cares about low noise because he wants to be able to measure faint signals, and he’s got to ensure that his noise floor is below what he’s trying to measure without resorting to multiplicative gain techniques that introduce further uncertainty.”

Not ultrafast,

but faster

figured out how to produce light of nanometer wavelengths, which somewhat paradoxically will need mid-IR lasers operating at 1.3 μm and longer, Murnane said.

With shorter wavelengths, the investigators will improve imaging resolution, since the classical diffraction limit is about half the wavelength. The push down from extreme-ultraviolet, at 13 nm, into x-rays as short as 1 nm should allow an equivalent enhancement in resolving object details.

There’s another effect of this approach,
Kapteyn said. “If you do it under the right
conditions, you generate an attosecond
pulse.”
Like the wavelength, the pulse duration
is thousands of times smaller than the ori-
ginal. Results indicate that pulses of about
5 as can be generated. At 10− 18 seconds, an
attosecond is so short that light travels only
one-third of a nanometer. These brief bursts
of light should allow the capture of electron
dynamics in materials and molecules.

For imaging, the researchers illuminate an object with a coherent beam and collect the scattered light. Visually, this looks like a mess, but it contains information from which spatial data can be extracted.

What’s more, light below 4 nm is absorbed by elements such as carbon and nitrogen and so can provide elemental information. In particular, water is relatively transparent in this region, but carbon is strongly absorbing, leading to an interesting possibility.

“You can image carbon content in an x-ray image with 10-nm resolution for a field of view that’s about the size of a single cell,” Kapteyn said.

Nonbiological uses of the technique could include tracking the dynamics of semiconductors by following transistor heat dissipation. For hard disks, changes in data bit magnetization could be measured, an important topic as the industry strives to make higher-capacity disks.

Imaging is done by having the energetic photons directly strike a CCD sensor, which causes some chip damage. The technique is also limited to imaging depths of only a few microns, and the beam itself has to travel in vacuum. The sample being imaged can sit in atmosphere, pressed up against a transparent window.