An ordinary

bubble Bubble, Bubbles or The Bubble may refer to: Common uses * Bubble (physics), a globule of one substance in another, usually gas in a liquid ** Soap bubble * Economic bubble, a situation where asset prices are much higher than underlying fundame ...

can serve as an optofluidic laser. These bubble lasers have been made of dye-doped soap solutions and smectic liquid crystal. In a bubble laser, the bubble itself serves as the

optical resonator An optical cavity, resonating cavity or optical resonator is an arrangement of mirrors or other optical elements that confines light waves similarly to how a cavity resonator confines microwaves. Optical cavities are a major component of lasers, ...

. Uniquely, bubble lasers exhibit hundreds of regularly spaced resonant frequencies called ''whispering gallery modes'', named for the Whispering Gallery in St. Paul's Cathedral in London. Researchers have found that the emission spectrum of a bubble laser is highly dependent on the bubble's environment; changing ambient

air pressure Atmospheric pressure, also known as air pressure or barometric pressure (after the barometer), is the pressure within the atmosphere of Earth. The Standard atmosphere (unit), standard atmosphere (symbol: atm) is a unit of pressure defined as , whi ...

electric field An electric field (sometimes called E-field) is a field (physics), physical field that surrounds electrically charged particles such as electrons. In classical electromagnetism, the electric field of a single charge (or group of charges) descri ...

s changes the size of the bubble (the optical resonator), and therefore the wavelengths of laser emission.

Description

Bubble lasers have been made from soap solutions to which a few drops of fluorescent

laser dye file:Coherent 899 dye laser.jpg, Close-up of a table-top dye laser using Rhodamine 6G as active medium. file:rhodamine 6G.svg, Molecular structure of Rhodamine 6G, perhaps the best known laser dye. A Laser dye is a dye used as laser medium in a dy ...

have been added. The fluorescent dye acts as the

gain medium The active laser medium (also called a gain medium or lasing medium) is the source of optical gain within a laser. The gain results from the stimulated emission of photons through electronic or molecular transitions to a lower energy state from ...

. When a pump laser is shone onto the bubble, the dye molecules are excited. The excited dye molecules emit photons. The light propagates along the surface of the soap bubble, leading to

wave interference In physics, interference is a phenomenon in which two coherent waves are combined by adding their intensities or displacements with due consideration for their phase difference. The resultant wave may have greater amplitude (constructive in ...

that generates distinct, evenly-spaced optical resonances of the bubble (called whispering gallery modes). When photons, by chance, of the right frequencies are emitted into the whispering gallery modes, it stimulates other molecules to emit more matching photons, amplifying the light. A soap bubble's thickness is constantly changing due to freely flowing water inside the bubble. This results in an unstable lasing spectrum. More stable results were achieved when the bubbles were made of smectic liquid crystal, which is made entirely of organic liquid-crystal molecules. These bubbles do not contain water, can be very thin, and can survive almost indefinitely.

Applications

The spacing of whispering gallery modes is directly related to the bubble's circumference. This means that bubble lasers may be used as pressure sensors. Bubble lasers have measured pressure changes as high as 100 bar (10,000 kPA) and as low as 1.5 Pa, an "exceptionally large" dynamic range, far outperforming other pressure sensors of comparable size. In the future, bubble lasers may be used to study thin films and phenomena such as

Cavity optomechanics Cavity optomechanics is a branch of physics which focuses on the interaction between light and mechanical objects on low-energy scales. It is a cross field of optics, quantum optics, solid-state physics and materials science. The motivation for r ...

References

{{Lasers, state=collapsed Bubbles (physics) Optofluidics Laser types Laser science

Description

Applications

See also

References