Scientists trap light in layer 1,000 times thinner than hair: Study

Researchers have created a nanoscale structure that traps infrared light in a layer just 40 nanometres thick over 1000 times thinner than a human hair By using a unique material with exceptional lightbending properties they can confine and intensify light far beyond previous limitsThis setup also dramatically boosts light conversion effects turning infrared into visible blue light The advance could pave the way for smaller faster photonic technologiesResearchers from the Faculty of Physics at the University of Warsaw working with teams from the Lodz University of Technology the Warsaw University of Technology and the Polish Academy of Sciences have created a structure capable of trapping infrared light in a layer just 40 nanometres thickTheir approach relies on a design known as a subwavelength grating made from a specialised material called molybdenum diselenide MoSe2 The findings were reported in the journal ACS NanoManipulating light at extremely small scales is key to advancing modern technology As traditional electronics begin to reach their limits photonics offers an alternative by using light instead of electrons to carry information because photons move faster and do not have mass like electrons devices based on light could become both quicker and smaller opening the door to more powerful and compact technologiesThe challenge of lights wavelengthLight behaves both as a particle and as a wave and this wave nature introduces a limitation Each type of light has a wavelength which determines how small a structure can be while still controlling it effectively Visible light has wavelengths of several hundred nanometres while infrared light extends to a micrometre or more This raises an important question can light be confined in structures smaller than its own wavelengthThe research team demonstrated that this is indeed possible By engineering a subwavelength grating they were able to trap infrared light within a layer only 40 nanometers thick This structure consists of closely spaced parallel strips that interact with light similarly to a prism When these strips are positioned closer together than the wavelength of light the grating can act like a nearperfect mirror while also holding the light inside a very small volumeWhy molybdenum diselenide works so wellEarlier versions of such gratings made from materials like silicon or gallium compounds required thicknesses of several hundred nanometers to function effectively Reducing their size caused them to lose their ability to confine light The key difference in this new approach is the use of molybdenum diselenide which has a much higher refractive index In simple terms light slows down more inside this material than in others While light slows by about 15 times in glass and roughly 35 times in silicon or gallium arsenide it slows by about 45 times in MoSe2 This strong slowing effect allows the structure to shrink dramatically while still trapping light efficiently resulting in a layer more than a thousand times thinner than a human hairTurning infrared light into blue lightMoSe2 also brings additional advantages Like graphene it forms layered structures but unlike graphene it is a semiconductor It also exhibits nonlinear optical behavior including a process known as third harmonic generation In this process three infrared photons combine into one photon with a higher frequency effectively converting infrared light into visible blue light Because the grating strongly concentrates infrared light this conversion becomes much more efficient The researchers found that the effect is more than 1500 times stronger compared to a flat layer of the same materialAnother major advance lies in how the material was produced Previously thin layers of MoSe2 were created using exfoliation a method similar to peeling layers off a crystal with adhesive tape While simple this technique is inconsistent and limited to very small areas typically around ten square micrometers which is not suitable for realworld devicesTo overcome this the team used molecular beam epitaxy MBE a wellestablished method for growing semiconductor layers This approach allowed them to produce large uniform MoSe2 films spanning several square inches Despite this large size the layer maintained a thickness of just 40 nanometers giving it an extreme aspect ratio For comparison the thicknesstosize ratio of this layer is about one to a million while a typical A4 sheet of paper has a ratio closer to 12000Toward practical photonic applicationsThese results suggest that molybdenum diselenide produced in this way could significantly change how light is controlled in future technologies Structures no longer need to be thick to manipulate light effectively Instead extremely thin layers can perform the same function and in some cases even better Because the production method is scalable the path toward realworld applications such as photonic integrated circuits is becoming increasingly realisticThis story 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