Light with a high frequency is useful. The shorter the wavelength of light, the smaller the objects and details it can see—the higher the frequency, the shorter the wavelength.
So violet light can show you more modest subtleties than red light, for instance, since it has a more limited frequency. However, to see minuscule things — down to the size of billionths of a meter, a great many times not exactly the width of a human hair — to see those things, you want outrageously bright light (and a decent magnifying instrument).
With wavelengths ranging from 10 to 120 nanometers, extreme ultraviolet light has numerous uses in medical imaging, studying biological objects, and deciphering the intricate details of computer chips as they are made. Nonetheless, delivering little and reasonable wellsprings of this light has been extremely difficult.
We have figured out how to make nanoparticles of a common semiconductor material emit light at a frequency that is up to seven times higher than the frequency of the light that is directed toward them. We created blue-violet light from infrared light, and producing outrageously bright light from red light with similar principles will be conceivable. Our exploration, done with partners from the College of Brescia, the College of Arizona, and Korea College, is distributed in Science Advances.
The power of harmonics
Our system begins with a standard laser that emits infrared light with a long wavelength. There is nothing special about this pump laser; such lasers are commercially available and can be small and affordable.
In any case, next we fire short beats of light from this laser at an extraordinarily designed nanoparticle of a material called aluminum gallium arsenide, and that is where things get fascinating.
The nanoparticle ingests energy from the laser heartbeats and, afterward, produces its own eruption of light. We are able to amplify certain harmonics of the emitted light by creating powerful resonances by carefully engineering the nanoparticle’s size and shape.
What exactly does that imply? Well, we can use sound as an analogy.
When you pull a string on a guitar, it vibrates with its fundamental frequency, which is the primary note you hear, and harmonics, which are multiples of the fundamental frequency, in small amounts. The guitar’s body is made to produce resonances that make some of these harmonics stronger and others weaker, making the whole sound you hear.
Music on a guitar string: in the basic recurrence, the frequency is the length of the entire string, yet in the higher music, different, more limited frequencies fit inside the length of the string. Credit: Wikimedia / Y Landman.
Both light and sound offer similarities in their material science: these are both engendering waves (acoustic waves on account of sound and electromagnetic waves on account of light).
In our light source, the siphon laser resembles the fundamental note of the string, and the nanoparticles resemble the guitar body. The nanoparticles, on the other hand, are unique in that they significantly amplify the pump laser’s higher harmonics, resulting in light with a higher frequency (up to seven times higher in our case) and a shorter wavelength.
What it’s great for
This innovation permits us to make new wellsprings of light in pieces of the electromagnetic range, like the super bright, where there are no regular wellsprings of light and where current designed sources are excessively enormous or excessively costly.
Using visible light, conventional microscopes can only examine objects down to about a ten-millionth of a meter in size. The goal is restricted by the frequency of light. The wavelength of violet light is approximately 400 nanometers (one nanometer is one billionth of a meter).
However, being able to see down to about a billionth of a meter would be extremely helpful in a lot of applications, such as biological imaging and electronics manufacturing.
“Super-resolution” microscopy, which allows you to see details smaller than the wavelength of the light you are using, or electron microscopes, which do not use light at all and create images using a flux of electrons, are currently required to see at those scales. However, these approaches are time-consuming and costly.
Consider computer chips to understand the advantages of our light source: they are made of exceptionally minuscule parts that include estimates of nearly as little as a billionth of a meter. Utilizing extreme ultraviolet light to monitor the process in real time during the manufacturing process would be helpful.
This would save assets and time on awful clusters of chips. The industry is so large that even a one percent increase in chip yields could result in annual savings of billions of dollars.
In the not-too-distant future, our kind of nanoparticles could be used to produce tiny, low-cost sources of extreme ultraviolet light that would illuminate the universe of extremely small things.
More information: Anastasiia Zalogina et al, High-harmonic generation from a subwavelength dielectric resonator, Science Advances (2023). DOI: 10.1126/sciadv.adg2655