Flexible Laser Droplets Produced with Simple Method

Flexible Laser Droplets Produced with Simple Method

Researchers at the University of Tsukuba’s Tsukuba Research Center for Energy Materials Science have successfully demonstrated a method for producing ionic liquid microdroplets that can function as flexible, durable, and pneumatically adjustable lasers.

Unlike current droplet lasers, which cannot be used in normal atmospheric conditions, this new development holds the potential for lasers that can be utilized in everyday environments.

Lotus plants are known for their beauty and their unique self-cleaning property, where water droplets form into near-perfect spheres and roll off the surface of the leaf taking any dust with them. This is due to microscopic bumps on the leaf.

Flexible Laser Droplets

Researchers at the University of Tsukuba have utilized this self-cleaning property to create liquid droplets that can function as lasers and remain stable for up to a month. This is an improvement over current droplet lasers which can only be used in enclosed containers and cannot operate in normal atmospheric conditions as they will quickly evaporate.

To create the laser droplets, an ionic liquid called 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIBF4) was mixed with a dye that enabled it to become a laser. This specific liquid was selected because it evaporates slowly and has a large surface tension. A quartz substrate was coated with tiny fluorinated silica nanoparticles to make it repel liquids, and when the EMIBF4 was deposited on it using a pipette, the resulting droplets remained spherical. The researchers found that the droplets remained stable for a minimum of 30 days.

According to Professor Hiroshi Yamagishi, the first author of the study, the droplet’s form and ability to resist evaporation were predicted by mathematical models to hold up even when exposed to gas convection. This shape and stability allows the droplet to maintain an optical resonance when activated by a laser pumping source. The researchers found that blowing nitrogen gas can adjust the laser peaks between 645 to 662 nm by altering the shape of the droplets slightly. According to Professor Yamagishi, this is the first liquid laser oscillator that can be tunable by gas convection.

According to the study’s first author, Professor Hiroshi Yamagishi, the ability of the laser droplet to maintain its shape and optical resonance even when exposed to gas convection makes it suitable for use as a highly sensitive humidity sensor or airflow detector. To demonstrate this potential, the researchers utilized a commercial inkjet printing device with a printer head that could handle viscous liquids.

The resulting arrays of laser droplets were found to function without the need for further treatment, indicating that the production process is highly scalable and easy to perform. This makes the technology promising for use in the manufacture of low-cost sensor or optical communication devices, and could potentially lead to the development of new airflow detectors and more affordable fiber-optics communications. The research has been published in the journal Laser & Photonics Reviews.

More information: Laser Droplets, Hiroshi Yamagishi et al, Pneumatically Tunable Droplet Microlaser, Laser & Photonics Reviews (2023). DOI: 10.1002/lpor.202200874