Lasers based on titanium-sapphire (Ti:sapphire) provide top performance in fields like quantum optics, spectroscopy, and neuroscience. But that performance comes at a steep cost of not just the multi-thousand dollar price tag, but space and power as well. Ti:sapphire lasers take up several cubic feet and require other high-powered lasers to supply them with enough energy to function. Despite their high level of performance and utility in cutting edge applications, their adoption in the industry has been slow. Making a jump from tabletop to the microscale, engineers at Stanford University have built a Ti:sapphire laser on a chip. According to the researchers, the prototype is four orders of magnitude smaller (10,000×) and three orders less expensive (1,000×) than any Ti:sapphire laser ever produced. The researchers’ Ti:sapphire laser is four orders of magnitude smaller (10,000x) and three orders less expensive (1,000x) than other Ti:sapphire lasers. Here, the laser is depicted leaning against a block of Ti:sapphire while sitting on a quarter. Courtesy of Yang et al., Nature. “Instead of one large and expensive laser, any lab might soon have hundreds of these valuable lasers on a single chip. And you can fuel it all with a green laser pointer,” said Jelena Vuckovic, Stanford’s Jensen Huang Professor in Global Leadership and senior author of the research. To fashion the new laser, the researchers began with a bulk layer of Ti:sapphire on a platform of silicon dioxide (SiO2), all riding atop true sapphire crystal. They then grind, etch, and polish the Ti:sapphire to an extremely thin layer just a few hundred nanometers thick. Into that thin layer, they then pattern a swirling vortex of tiny ridges, or a waveguide. These ridges are like fiber-optic cables, guiding the light around and around, building in intensity. “Mathematically speaking, intensity is power divided by area. So, if you maintain the same power as the large-scale laser, but reduce the area in which it is concentrated, the intensity goes through the roof,” said Joshua Yang, a doctoral candidate in Vuckovic’s lab and co-first author. “The small scale of our laser actually helps us make it more efficient.” A Ti:sapphire waveguide amplifier created by the researchers that fits in a 0.5mm square. Courtesy of Yang et al., Nature. A microscale heater that warms the light traveling through the waveguides is then added, allowing the team to change the wavelength of the emitted light to tune the color of the light anywhere between 700 nm and 1,000 nm – in the red to infrared range. “When you leap from tabletop size and make something producible on a chip at such a low cost, it puts these powerful lasers in reach for a lot of different important applications,” Yang said. These applications include areas like quantum physics, where the laser could provide an inexpensive and practical solution to scale down state-of-the-art quantum computers. Medical fields could see the Ti:sapphire lasers being used for optogenetics or in compact optical coherence tomography technologies for ophthalmology. The researchers are currently working on next steps for perfecting their chip-scale Ti:sapphire laser as well as on ways to mass-produce them on wafers and bring them to market. The research was published in Nature (www.doi.org/10.1038/s41586-024-07457-2).
