Most accelerators, including the big ones at CERN and RHIC, use charged particles: protons, electrons, or ions (atoms with electrons removed to make them positively charged). That’s because it’s easy to accelerate that kind of particle using electric and magnetic fields. However, neutral particles like neutrons or normal atoms can’t be accelerated by those fields, even though they could be useful for particle colliders or bombarding materials for various reasons. A new multi-step method has solved that problem by accelerating ions, then restoring the electrons, leading to very energetic neutral atoms.

As we all know from elementary school physics, like charges repel. So any positively charged particle added to the plasma will experience acceleration from the plasma waves. Laser plasma accelerators are more compact than many other accelerator designs, including those used in big experiments like the Large Hadron Collider (LHC), although they haven’t yet reached the same energies. Plasma acceleration (sans lasers) is also important in many astrophysical processes. [Read more….]

Accelerating neutral particles on a lab bench

Laser cooling (also known as optical cooling) is a well-established technique…but mostly for gases. The basic idea is to disperse the thermal energy of the atoms through shining light on them: the frequency of the laser is set to be slightly lower than the energy of transition between two configurations in the atoms, so that atoms’ motion provides that extra bit to lead to absorption. That converts energy of motion (kinetic energy) into light, slowing the atoms down. However, the trick doesn’t work for solids, because the kinetic energy takes the form of phonons, quasiparticles of sound. However, researchers figured out a way to annihilate the phonons using a laser, in a particular type of semiconductor. Using that trick, they cooled the material down by 40 degrees, opening the way to rapid refrigeration of some solids.

The authors of the new study used cadmium sulphide (CdS), a material known as a group-II-VI semiconductor. Commonly used in digital electronics, semiconductors are insulators under normal conditions, but can be induced to conduct electricity when impurity atoms are added. Group-II-VI semiconductors host both strong phonons, and an additional type of particle-like excitation known as an exciton. Excitons are created through interactions between electrons and “holes” that the electrons left behind. [Read more...]

Rapid cooling of semiconductors using lasers (but no sharks)

I admit, I love flipping through SkyMall when I’m on airplanes. However, the catalog is chock-full of pseudoscience, as with today’s entry in “As Seen on TV!”, my occasional feature over at Double X Science. (Warning: contains my balding scalp.)

Ah, lasers. They may not have the mystique of magnets or the nous of “natural”, but they are a frequent ingredient in modern snake oil. (Come to think of it, one of the hair-restoration products may have contained snake oil. I don’t want to ask.) But while lasers can help correct nearsightedness in some cases, perform minimally invasive surgeries, and remove hair, color my scalp skeptical about their ability to restore hair. [Read more…]

The bald(ing) truth about laser hair-restoration treatments