Researchers build an RGB laser using quantum dots

Lasers produce nearly monochromatic light. However, not all applications demand pure, single-color light—digital displays and other devices require a wide range of colors. While it is possible to combine red, green, and blue (RGB) lasers to replicate the whole visible-light spectrum, current technology requires using three different types of lasers.

Researchers have now produced a single material capable of producing several wavelengths of laser light. Cuong Dang et al. constructed a full RGB laser using colloidal quantum dots (CQDs), thin films that produce light via quantum excitations. The size of a quantum dot determines the color of the light it emits, so by overlaying many small patches of CQDs on surface, the researchers observed broad-spectrum emission. While their device is not yet practical, it represents significant progress toward multi-wavelength, single-material lasers.

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First superradiant lasers produce nearly no photons (and that’s expected)

Lasers by their nature emit light where each photon has nearly the same frequency. That "nearly" is good enough for most applications, but there are still cases where we'd like to do better: atomic clocks, gravitational wave detectors, and tests of variations in physical constants. All of these bump up against the limits of current lasers. A laser with a more stable frequency known as a superradiant laser has been studied theoretically, and now a prototype has been built shows what must be done to make it a practical reality.

Justin G. Bohnet et al. (of JILA/NIST) constructed a demonstration superradiant laser using ultracold rubidium atoms, in which the laser's photons act to synchronize the electronic transitions within the atoms. While a standard laser has many photons present in the laser cavity, this superradiant laser has a cavity that, at any given time, may be empty of photons. Where in a normal laser the light is coherent and the atoms are uncorrelated, in a superradiant laser, it's the atoms that are coherent, transitioning between energy states in concert. While the prototype is not a fully-working superradiant laser, it shows what steps are necessary to construct the real thing, and demonstrates how it should work.

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Researchers develop a frequency comb that can untangle the extreme ultraviolet spectrum

Performing atomic, molecular, and optical measurements at high precision requires very precisely calibrated optical equipment. One method for achieving precision, which won its developers the 2005 Nobel Prize in physics, is known as a frequency comb. These combs create a clear series of evenly-spaced spectral lines that can be put to a variety of uses. Until now, frequency combs have been confined to visible light frequencies, but new developments have extended their usefulness into the extreme ultraviolet portion of the spectrum. The extreme UV corresponds to quantum transitions in many molecules, as well as nuclear oscillations that may power the next generation of nuclear clocks.

Researchers (Arman Cingöz, Dylan C. Yost, Thomas K. Allison, Axel Ruehl, Martin E. Fermann, Ingmar Hartl, and Jun Ye) in Colorado and Michigan built a frequency comb that produces attosecond-range pulses of light. (One attosecond is 10^-18 second, or one quintillionth of a second.) Directing this into a special cavity containing xenon gas, they produced a clear coherent spectrum spanning the extreme ultraviolet.

This not only improves on previous experiments in ultraviolet optical combs; it may provide a new test for potential variations in the fine-structure constant, one of the fundamental physical constants.

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Bringing galaxy-scale magnetic fields down to size in the lab

For a variety of obvious reasons, it's impossible to reproduce the exact environment in which galaxies form. The lack of direct experimental tests for a the models astrophysicists use creates a disconnect between what astronomers observe and theoretical work. However, that barrier is being broken down by a combination of high-powered lasers and a new understanding of how lab-scale experiments can be related to vastly larger systems such as galaxies.

Researchers at the Laboratoire pour l'Utilisation de Lasers Intenses (LULI), along with colleagues at various universities, have successfully simulated the magnetic fields that form in early galaxies. Naively, there seems to be no correspondence between the experiment and the real astrophysical system. The lab set-up is very small, works on a very short time frame, and uses carbon rods and lasers; the real environment for galaxy formation is clouds of gas and dark matter, and the time-scale is hundreds of millions of years. Nevertheless, a magnetic field strength (along with other effects) has been observed in the lab that corresponds to that experienced by early protogalaxies.

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A laser that works better shaken, not stirred

I don't know about you, but when I think of lasers, I think of boxes on heavy, stabilized tables. Inside the boxes, the optical elements are mounted on stabilized mounts and everything is generally held as solidly in place as possible. The one thing that you generally don't do is give a laser a good shaking. Unless it has already stopped working, in which case, have at it... preferably with a hammer.

Finding a paper that demonstrated a laser with better performance when it was being shaken compared to when it was held came as a bit of a shock.

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Category Archives: lasers

Researchers build an RGB laser using quantum dots

First superradiant lasers produce nearly no photons (and that’s expected)

Researchers develop a frequency comb that can untangle the extreme ultraviolet spectrum

Bringing galaxy-scale magnetic fields down to size in the lab

A laser that works better shaken, not stirred