Fysikere skabte en mikrolaser, der udsender to cirkulære stråler

Forskere fra University of Warszawa, Military University of Technology og University of Southampton præsenterede en ny type afstembar mikrolaser, der udsender to stråler. "Disse stråler er polariseret cirkulært og rettet i forskellige vinkler," siger prof. Jacek Szczytko fra fakultetet for fysik ved universitetet i Warszawa. Denne præstation blev opnået ved at skabe den såkaldte persistent-spin helix på overfladen af ​​mikrohulrummet. Resultaterne er blevet offentliggjort i Physical Review Applied .

For at opnå denne effekt fyldte videnskabsmænd det optiske mikrohulrum med en flydende krystal doteret med et organisk laserfarvestof. Mikrohulrummet består af to perfekte spejle placeret tæt på hinanden - i en afstand på 2-3 mikron - så der dannes en stående elektromagnetisk bølge indeni. Rummet mellem spejlene var fyldt med et specielt optisk medium - flydende krystal - som desuden var organiseret ved hjælp af en speciel spejlbelægning.

"Det karakteristiske træk ved flydende krystaller er deres aflange molekyler, og billedligt talt blev de 'kæmmet' på overfladen af ​​spejlene og kunne rejse sig under påvirkning af et eksternt elektrisk felt og dreje også andre molekyler, der fylder hulrummet," siger første forfatter, Marcin Muszynski, fra fakultetet for fysik ved universitetet i Warszawa.

Lyset i hulrummet interagerer med molekylerne på forskellige måder, når den udbredte bølges elektriske felt svinger langs molekylerne, og når svingningerne er vinkelrette på dem. Den flydende krystal er et dobbeltbrydende medium - det kan karakteriseres ved to brydningsindekser, som afhænger af retningen af ​​de elektriske feltoscillationer (dvs. den såkaldte elektromagnetiske bølgepolarisation).

Det præcise arrangement af molekyler inde i lasermikrohulrummet, opnået ved Military University of Technology, resulterede i fremkomsten af ​​to lineært polariserede lystilstande i hulrummet - dvs. to stående lysbølger med modsatte lineære polariseringer. Det elektriske felt ændrede orienteringen af ​​molekylerne inde i det optiske hulrum, hvilket ændrede det effektive brydningsindeks for de flydende krystallag. Således styrede den længden af ​​den såkaldte optiske lysvej - produktet af hulrummets bredde og brydningsindekset, som energien (farven) af det udsendte lys afhænger af. One of the modes did not change its energy as the molecules rotated, while the energy of the other increased as the orientation of the molecules changed.

By optically stimulating the organic dye placed between the molecules of the liquid crystal, a lasing effect was obtained—coherent light radiation with a strictly defined energy. The gradual rotation of the liquid crystal molecules led to unexpected properties of this lasing. The lasing was achieved for this tunable mode:The laser emitted one linearly polarized beam perpendicular to the surface of the mirrors. The use of liquid crystals allowed for a smooth tuning of the light wavelength with the electric field by as much as 40 nm.

"However, when we rotated the liquid crystal molecules so that both energy of modes—the one sensitive to the orientation of the molecules and the one that did not change its energy—overlapped (that is, they were in resonance), the light emitted from the cavity suddenly changed its polarization from linear to two circular:right- and left-handed, with both circular polarities propagating in different directions, at an angle of several degrees," says Prof. Jacek Szczytko, from the Faculty of Physics of the University of Warsaw.

The phase coherence of the laser has been confirmed in an interesting way. "The so-called persistent-spin helix—pattern of stripes with different polarization of light, spaced 3 microns apart—appeared on the surface of the sample. Theoretical calculations show that such a pattern can be formed when two oppositely polarized beams are phase coherent and both modes of light are inseparable—this phenomenon is compared to quantum entanglement," explains Marcin Muszynski.

So far, the laser works in pulses because the organic dye that was used slowly photodegrades under the influence of intensive light. Scientists hope that replacing the organic emitter with more durable polymers or inorganic materials (e.g., perovskites) will allow for longer lifetime.

"The obtained precisely tunable laser can be used in many fields of physics, chemistry, medicine and communication. We use nonlinear phenomena to create a fully optical neuromorphic network. This new photonic architecture can provide a powerful machine learning tool for solving complex classification and inference problems, and for processing large amounts of information with increasing speed and energy efficiency," adds Prof. Barbara Pietka, from The Faculty of Physics UW. + Udforsk yderligere

The optical Stern-Gerlach Deflection and Young's experiment in the reciprocal space