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About 5,914 papers for “Lasing threshold”

Low-Threshold Bidirectional Air Lasing

Alexandre Laurain, Maik Scheller, Pavel Polynkin · Physical Review Letters · 2014

Air lasing refers to the remote optical pumping of the constituents of ambient air that results in a directional laserlike emission from the pumped region. Intense current investigations of this concept are motivated by the potential applications in remote atmospheric sensing. Different approaches to air lasing are being investigated, but, so far, only the approach based on dissociation and resonant two-photon pumping of air molecules by deep-UV laser pulses has produced measurable lasing energies in real air and in the backward direction, which is of the most relevance for applications. However, the emission had a high pumping threshold, in hundreds of GW/cm^{2}. We demonstrate that the threshold can be virtually eliminated through predissociation of air molecules with an additional nanosecond laser. We use a single tunable pump laser system to generate backward-propagating lasing in both oxygen and nitrogen in air, with energies of up to 1 μJ per pulse.

Cited by 84

Low-threshold lasing in photonic-crystal heterostructures

M. Srinivas Reddy, R. Vijaya, Ivan D. Rukhlenko et al. · Optics Express · 2014

We study a photonic crystal (PhC) heterostructure cavity consisting of gain medium in a three-dimensional (3D) PhC sandwiched between two identical passive multilayers. For this structure, based on Korringa-Kohn-Rostoker method, we observe a decrease in the lasing threshold of two orders of magnitude, as compared with a stand-alone 3D PhC. We attribute this remarkable decrease in threshold gain to the overlap of the defect cavity mode with the reduced group velocity region of the PhC's dispersion, and the associated enhancement in the distributed feedback from the ordered layers of the PhC. The obtained results show the potency for designing PhC-based, compact on-chip lasers with ultra-low thresholds.

Cited by 20Open access

Tracking exceptional points above the lasing threshold

Kaiwen Ji, Qi Zhong, Li Ge et al. · Nature Communications · 2023

Recent studies on exceptional points (EPs) in non-Hermitian optical systems have revealed unique traits, including unidirectional invisibility, chiral mode switching and laser self-termination. In systems featuring gain/loss components, EPs are commonly accessed below the lasing threshold, i.e., in the linear regime. In this work, we experimentally demonstrate that EP singularities in coupled semiconductor nanolasers can be accessed above the lasing threshold, where they become branch points of a nonlinear dynamical system. Contrary to the common belief that unavoidable cavity detuning impedes the formation of EPs, here we demonstrate that such detuning is necessary for compensating the carrier-induced frequency shift, hence restoring the EP. Furthermore, we find that the pump imbalance at lasing EPs varies with the total pump power, enabling their continuous tracking. This work uncovers the unstable nature of EPs above laser threshold in coupled semiconductor lasers, offering promising opportunities for the realization of self-pulsing nanolaser devices and frequency combs.

Cited by 33Open access

Ultralow-threshold Raman lasing with CaF_2 resonators

Ivan S. Grudinin, Lute Maleki · Optics Letters · 2006

We demonstrate efficient Raman lasing with CaF2 whispering-gallery-mode resonators. Continuous-wave emission threshold is shown to be possible below 1 microW with a 5mm cavity, which is to our knowledge orders of magnitude lower than in any other Raman source. Low-threshold lasing is made possible by the ultrahigh optical quality factor of the cavity, of the order of Q=5x10(10). Stokes components of up to the fifth order were observed at a pump power of 160 microW, and up to the eighth order at 1 mW. A lasing threshold of 15 microW was also observed in a 100 microm CaF2 microcavity. Potential applications are discussed.

Cited by 89

Low Threshold Lasing in Cholesteric Liquid Crystals

Bahman Taheri, Antonio Muñoz, Peter Palffy‐Muhoray et al. · Molecular crystals and liquid crystals science technology. Section A, Molecular crystals and liquid crystals/Molecular crystals and liquid crystals science and technology. Section A, Molecular crystals and liquid crystals · 2001

Abstract Cholesteric liquid crystals, due to their periodic structure and large birefringence, are 1-d photonic band-gap materials. Circularly polarized light of the same handedness as the cholesteric structure cannot propagate in the reflection band. We have studied the effects of this band-gap structure on the fluorescence spectrum of dyes dissolved in the cholesteric liquid crystal, as well as on the fluorescence spectrum of the liquid crystal itself. We have found that emission is enhanced at the band edges, and, above a certain pump threshold, lasing occurs both in dye-doped and in pure liquid crystals. Extremely low lasing thresholds and high efficiencies were observed in dye-doped systems. The results suggest an active energy transfer mechanism between the LC host and the fluorescent dye molecules.

Cited by 106

Low-threshold lasing in novel microdisk geometries

Brian Corbett, John Justice, L. Considine et al. · IEEE Photonics Technology Letters · 1996

We have fabricated arrays of semiconductor microdisks with diameters from 3.5-9 μm using wet chemical etching in combination with epitaxial lift-off and metallic bonding techniques. The microdisks are supported on glass for higher optical confinement and to allow novel annular geometries. The optically pumped microdisks have high-Q (>2000) modes, low-pump thresholds (<20 μW) and multimode lasing at liquid nitrogen temperatures. Successive modes are excited by temperature tuning the bandgap.

Cited by 27

Lasing Threshold in Nanolasers with Extreme Dielectric Confinement

Marco Saldutti, Yi Yu, Jesper Mørk · 2023

Nanolasers based on emerging dielectric cavities with deep sub-wavelength optical confinement may offer an unprecedented light-matter coupling rate, near-unity spontaneous emission factor, and ultra-low threshold current. However, the extreme dielectric confinement in these nanolasers questions the standard approach to identifying the lasing threshold. Here, we discuss a new threshold definition, valid from the macro to the nanoscale and reflecting the recycling process that photons undergo in nanolasers with extreme dielectric confinement.

Cited by 0

Searching for Lasing Threshold in a Thresholdless Laser

Chi‐Wai Chow, F. Jahnke, Christopher Gies · OSTI OAI (U.S. Department of Energy Office of Scientific and Technical Information) · 2014

A quantum-optical model is applied to address the question of criteria for lasing in a threshold less laser where the intensity jump, customarily used to indicate transition to lasing, is missing.

Cited by 1Open access

Second-order coherence across the Brillouin lasing threshold

Cryer-Jenkins, Evan, Enzian, Georg, Freisem, Lars et al. · Figshare · 2023

Brillouin--Mandelstam scattering is one of the most accessible nonlinear optical phenomena and has been widely studied since its theoretical discovery one hundred years ago. The scattering mechanism is a three-wave mixing process between two optical fields and one acoustic field and has found a broad range of applications spanning microscopy to ultra-narrow-linewidth lasers. Building on the success of utilizing this nonlinearity at a classical level, a rich avenue is now being opened to explore Brillouin scattering within the paradigm of quantum optics. Here, we take a key step in this direction by employing quantum optical techniques yet to be utilized for Brillouin scattering to characterize the second-order coherence of Stokes scattering across the Brillouin lasing threshold. We use a silica microsphere resonator and single-photon counters to observe the expected transition from bunched statistics of thermal light below the lasing threshold to Poissonian statistics of coherent light above the threshold. Notably, at powers approaching the lasing threshold, we also observe super-thermal statistics, which arise due to instability and a ``flickering” in and out of lasing as the pump field is transiently depleted. The statistics observed across the transition, including the ``flickering'', are a result of the full nonlinear three-wave mixing process and cannot be captured by a linearized model. These measurements are in good agreement with numerical solutions of the three-wave Langevin equations and are well demarcated by analytical expressions for the instability and the lasing thresholds. These results demonstrate that applying second-order-coherence and photon-counting measurements to Brillouin scattering provides new methods to advance our understanding of Brillouin scattering itself and progress toward quantum-state preparation and characterization of acoustic modes.

Cited by 0Open access

Low-threshold lasing in active opal photonic crystals

M. Srinivas Reddy, R. Vijaya, Ivan D. Rukhlenko et al. · Optics Letters · 2013

We theoretically study a low-threshold band-edge lasing in three-dimensional photonic crystals (PhCs) with a face-centered cubic lattice structure, using a complex-valued permittivity approach combined with the Korringa-Kohn-Rostoker method. We show that the lasing threshold at the low-frequency band edge is smaller than that at the high-frequency band edge for the first-order stop band of the PhC. We also analyze the impact of the number of the PhC's layers on the frequency of band-edge lasing and the lasing threshold near the first-order stop band in the ΓL direction, and demonstrate a broad tunability of the lasing frequency with change in the emission collection angle. The obtained results are beneficial for the performance enhancement of tunable, PhC-based chip lasers.

Cited by 13

Low-threshold organic lasing from semiconducting nanomolecular systems

Wen‐Yong Lai, Wei Huang · 2011

Organic laser diodes have long been a goal for semiconductor scientists, and a lot of research efforts in the past decade have focused attention on small-molecule or polymer semiconductors as a photonic platform. We present here our recent advances on the development of low-threshold organic lasing from well-defined semiconducting nanomolecular systems that combine precise chemical structures with good solution processibility and amorphous morphological stability.

Cited by 0

Lasing Threshold and Mode Competition in Chaotic Cavities

Misirpashaev, T. Sh., Beenakker, C. W. J. · arXiv (Cornell University) · 1997

The lasing threshold is studied of a multi-mode chaotic cavity (linear size D &gt;&gt; wavelength λ) coupled to the outside through a small hole (linear size d &lt;&lt; λ). For sufficiently weak absorption by the boundaries, the statistical distribution of the threshold is wide, its mean value being much less than the pumping rate needed to compensate the average loss. The average number N_{nc} &gt;&gt; 1 of non-competing excited modes is proportional to the square root of the pumping rate. We use the classical model of spatial hole burning to account for mode competition and find a reduction in the average number of excited modes to N =3^{1/3} N_{nc}^{2/3}.

Cited by 0Open access

Second-order coherence across the Brillouin lasing threshold

Cryer-Jenkins, Evan, Enzian, Georg, Freisem, Lars et al. · Figshare · 2023

Brillouin--Mandelstam scattering is one of the most accessible nonlinear optical phenomena and has been widely studied since its theoretical discovery one hundred years ago. The scattering mechanism is a three-wave mixing process between two optical fields and one acoustic field and has found a broad range of applications spanning microscopy to ultra-narrow-linewidth lasers. Building on the success of utilizing this nonlinearity at a classical level, a rich avenue is now being opened to explore Brillouin scattering within the paradigm of quantum optics. Here, we take a key step in this direction by employing quantum optical techniques yet to be utilized for Brillouin scattering to characterize the second-order coherence of Stokes scattering across the Brillouin lasing threshold. We use a silica microsphere resonator and single-photon counters to observe the expected transition from bunched statistics of thermal light below the lasing threshold to Poissonian statistics of coherent light above the threshold. Notably, at powers approaching the lasing threshold, we also observe super-thermal statistics, which arise due to instability and a ``flickering” in and out of lasing as the pump field is transiently depleted. The statistics observed across the transition, including the ``flickering'', are a result of the full nonlinear three-wave mixing process and cannot be captured by a linearized model. These measurements are in good agreement with numerical solutions of the three-wave Langevin equations and are well demarcated by analytical expressions for the instability and the lasing thresholds. These results demonstrate that applying second-order-coherence and photon-counting measurements to Brillouin scattering provides new methods to advance our understanding of Brillouin scattering itself and progress toward quantum-state preparation and characterization of acoustic modes.

Cited by 0Open access

Low threshold room-temperature lasing of CdS nanowires

Sebastian Geburt, Andreas Thielmann, Robert Röder et al. · Nanotechnology · 2012

The synthesis of CdS nanostructures (bands, wires, irregular structures) was investigated by systematic variation of temperature and gas pressure, to deduce a comprehensive growth phase diagram. The high quality nanowires were further investigated and show stoichiometric composition of CdS as well as a single-crystalline lattice without any evidence of extended defects. The luminescence of individual nanowires at low excitation shows a strong near band edge emission at 2.41 eV indicating a low point defect concentration. Sharp peaks evolve at higher laser power and finally dominate the luminescence spectrum. The power dependence of the spectrum clearly shows all the characteristics of amplified stimulated emission and lasing action in the nanowire cavity. A low threshold was determined as 10 kW cm(-2) for lasing at room temperature with a slope efficiency of 5-10% and a Q factor of up to 1200. The length and diameter relations necessary for lasing of individual nanowires was investigated.

Cited by 52Open access

Low-threshold lasing in active opal photonic crystals

REDDY, MS, VIJAYA, R, RUKHLENKO, ID et al. · DSpace (IIT Bombay) · 2014

We theoretically study a low-threshold band-edge lasing in three-dimensional photonic crystals (PhCs) with a face-centered cubic lattice structure, using a complex-valued permittivity approach combined with the Korringa-Kohn-Rostoker method. We show that the lasing threshold at the low-frequency band edge is smaller than that at the high-frequency band edge for the first-order stop band of the PhC. We also analyze the impact of the number of the PhC's layers on the frequency of band-edge lasing and the lasing threshold near the first-order stop band in the GL direction, and demonstrate a broad tunability of the lasing frequency with change in the emission collection angle. The obtained results are beneficial for the performance enhancement of tunable, PhC-based chip lasers. (C) 2013 Optical Society of America

Cited by 0

Nanowire Oligomer Waveguide Modes towards Reduced Lasing Threshold

Henrik Mäntynen, Nicklas Anttu, Harri Lipsanen · Materials · 2020

Semiconductor nanowires offer a promising route of realizing nanolasers for the next generation of chip-scale optoelectronics and photonics applications. Established fabrication methods can produce vertical semiconductor nanowires which can themselves act both as a gain medium and as a Fabry-Pérot cavity for feedback. The lasing threshold in such nanowire lasers is affected by the modal confinement factor and end facet reflectivities, of which the substrate end reflectivity tends to be limited due to small refractive index contrast between the nanowire and substrate. These modal properties, however, also depend strongly on the modal field profiles. In this work, we use numerical simulations to investigate waveguide modes in vertical nanowire oligomers (that is, arrangements of few vertical nanowires close to each other) and their modal properties compared to single nanowire monomers. We solve for the oligomer waveguide eigenmodes which are understood as arising from interaction of monomer modes and further compute the reflectivity of these modes at the end facets of the nanowires. We consider either the nanowires or an additional coating layer as the gain medium. We show that both types of oligomers can exhibit modes with modal properties leading to reduced lasing threshold and also give directions for further research on the topic.

Cited by 5Open access