Room temperature sub-diffractional plasmon laser
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Room temperature sub-diffractional plasmon laser R.-M. Ma1, R. F. Oulton1, V. J. Sorger1, G. Bartal and X. Zhang1,2 1
NSF Center for Scalable and Integrated Nanomanufacturing, 3112 Etcheverry Hall, University of California, Berkeley, CA 94720 2 Materials Sciences Division Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, CA 94720 Email: [email protected]
ABSTRACT We report plasmon lasers with strong cavity feedback and optical confinement to 1/20th wavelength. Strong feedback arises from total internal reflection of plasmons, while confinement enhances the spontaneous emission rate by up to 18 times. INTRODUCTION Lasers have come a long way in the 50 years since their first demonstration. While lasers have overcome numerous technological limitations in recent years, scaling of their size below the diffraction limit of light has remained a fundamental challenge. Plasmon lasers can now create and sustain coherent light well below the diffraction limit [1-4], by generating and amplifying surface plasmon polaritons, collective electronic oscillations of metal-dielectric interfaces. The high power, coherent and deep sub-wavelength optical field inside plasmon lasers have the unique ability to drastically enhance light-matter interactions bringing fundamentally new capabilities to bio-sensing, data storage, photolithography and optical communications. The nano-scale physical size of plasmon lasers is another major advantage that can reconcile the device footprints of optical and electronic systems. However, these important applications require room temperature operation of sub-diffraction limited lasers, which remains a major hurdle [1, 2]. Recent works have addressed only one of two critical challenges: mitigating high metal loss due to strong mode confinement and creating strong feedback to minimize the high cavity loss of small photonic structures. Plasmon lasers capped in metal provide sufficient cavity feedback, but they exhibit limited confinement and high metal loss [2]. On the other hand, open plasmon lasers can achieve strong confinement with low metal loss, but suffer from scattering that limits feedback and imposes a minimum nanowire length [1]. While cryogenic temperatures have enabled sufficient gain in amplifying media to observe surface plasmons lasing, room temperature operation requires devices with a low metal loss confinement mechanism, effective cavity feedback and high gain materials all within a single nano-scale package. RESULT and DISCUSSION Here we report a room temperature plasmon laser with a sub-wavelength mode size of /20. The device consists of a 45 nm thick, 1 m length single crystal Cadmium Sulfide (CdS) square atop a Silver surface separated by a 5 nm thick Magnesium Fluoride gap layer, as shown in Fig. 1(a). Remarkably, the thickness of this device is comparable to the gate size of transistors in commercial chip-architecture; a truly nanoscopic device. Efficient feedback arises from total internal reflection of confined surface plasmons at the cavity boundaries and s
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