Terahertz vcsel
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This document proposes a vertical cavity surface emitting terahertz laser based on polariton lasers. A two-photon absorption process is used to excite a 2p exciton state, which then populates the 1s polariton state via THz transition. The population of the 1s state then stimulates additional THz transitions. Simulations show that the THz emission rate increases at the polariton lasing threshold, and that the 1s population increases exponentially above threshold. A hybrid GaN/GaAs design is proposed that could operate at room temperature without doping and emit both blue and red light to indicate THz emission.
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Terahertz time domain spectroscopy is a technique that uses short pulses of terahertz radiation to investigate materials. It can provide information about molecular vibrations and rotations through terahertz absorption spectroscopy. Key points:
- Terahertz radiation has energies between infrared and microwave frequencies, making it suitable for probing inter- and intra-molecular vibrations and rotations.
- Terahertz pulses are generated using ultrafast lasers and nonlinear crystals or photoconductive antennas, and detected using electro-optic sampling.
- Terahertz spectroscopy can identify functional groups in molecules and investigate properties of gases, liquids, crystals, and biologically relevant samples like sugars. It has applications in chemical identification and security imaging
Far infrared (terahertz) technology
This document discusses terahertz (THz) technology and optical detection of THz radiation using nonlinear parametric upconversion. It describes using a bulk gallium arsenide (GaAs) crystal to mix a 1550 nm optical pump with a 700 GHz THz beam from a backward wave oscillator, generating an optical idler signal at 1555.6 nm. Experimental results showed a THz-to-optical photon conversion efficiency of 0.001%. Improving efficiency requires phase matching, which can be achieved using quasi-phase matching by bonding GaAs crystals with alternating orientations.
Optical Computing
1) The presentation discusses optical computing, which uses photons in light beams rather than electric currents to perform computations. It has advantages like speed, easy manipulation of light, and suitability for parallelization.
2) Optical computing is developing in two directions - hybrid systems that use optics alongside existing computer architectures, and new optical-only computers. Key components discussed include VCSEL lasers, smart pixel technology, and WDM for sending multiple wavelengths through a single fiber.
3) Potential benefits of optical computing include much higher speeds, smaller size, higher bandwidth, and less heat generation compared to electronic computers. However, challenges remain around high power needs, interference effects, and cost of optical
Terahertz_An introduction
This document discusses terahertz frequency, which lies between infrared and microwave frequencies in the electromagnetic spectrum. It provides a brief history of terahertz science and outlines some key properties, including its ability to penetrate many materials and resolve fine spatial details. The document then describes several applications of terahertz technology, such as security scanning, medical imaging, manufacturing quality control, and astronomy. However, it notes that terahertz equipment remains large and difficult to implement in real-world settings.
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Terahertz vcsel
- 1. Vertical Cavity Surface Emitting Terahertz Lasers Alexey Kavokin (SOLAB, St-Petersburg) Ivan Shelykh (University of Iceland) Tomas Taylor (University of Southampton) Mikhail Glazov (Ioffe Physico-Technical Institute)
- 2. Polariton Lasers GaAs, T=40K E. Wertz et al., CdTe, T=50K APL 95, 051108 (2009) J. Kasprzak et al. Nature ,443, 409 (2006) J. Kasprzak et al. PRL ,101, 146404 (2008) GaN, T=300K ZnO, T=300K G. Christmann et al., Thierry Guillet, this conference APL 93, 051102 (2008)
- 3. Vertical Cavity Surface Emitting Terahertz Lasers based on Polariton Lasers • Excitation of a 2p exciton state by a two-photon absorption • 1s polariton state populated due to the THz transition from 2p state • Polariton population of 1s state stimulates the THz transition • Per each visible photon the device emits a THz photon • Vertical geometry! No terahertz cavity needed!
- 5. 1s – 2p terahertz transition in a microcavity J.L. Tomaino et al., arXiv:1112.2185v1
- 6. Coherent injection of microcavity polaritons through two-photon absorption Polariton lasing with a two-photon pump in a pillar GaAs microcavity Courtesy of Alberto Bramati, Elisabeth Giacobino, LKB, Paris
- 7. Theoretical treatment Liouville equation for the density matrix Master equation Rate equations: Second order coherence of pumping light 2p-population 1s-population Terahertz population
- 8. Terahertz VCSEL: results of simulation • Terahertz emission rate increases at the onset of polariton lasing • 2p population saturates • 1s population increases exponentially at lasing threshold New quantum optical effect: Threshold depends on the statistics of photons of pump!
- 9. Schematic of a hybrid GaAs/GaN terahertz polariton laser THz light Blue light GaN based microcavity T=300 K No doping needed! GaN: E(2p)=2ℏω(LED) Red Light Emitting Diode based on GaAs
- 10. Conclusions • Polariton lasers: low threshold coherent light sources, realised in GaAs, CdTe, GaN, ZnO,… • Two photon pumping of polariton lasers allows building a THz source • Polariton mediated THz lasers based on GaN: compact, room temperature, vertical geometry, no THz cavity needed • Hybrid blue light/THz lasers: one can see where to shoot! A.V. Kavokin, I.A. Shelykh, T. Taylor, M. Glazov, arXiv.org > cond-mat > arXiv:1201.4010