Optically pumped wavelength-tunable lasing from a GaN beam cavity with an integrated Joule heater pivoted on Si

Dynamically tunable laser sources are highly promising for realizing visionary concepts of integrated photonic circuits and other applications. In this paper, a Ga N-based laser with an integrated PN junction heater on Si is fabricated.The photoluminescence properties of the Ga N beam cavity are controlled by temperature, and the Joule heater provides electrically driven regulation of temperature. These two features of the cavity make it possible to realize convenient tuning of the lasing properties. The multi-functional Ga N beam cavity achieves optically pumped lasing with a single mode near 362.4 nm with a high Q-factor of 1394. The temperature of this device increases by 0–5℃ under the Joule heating effect. Then, electrical control of the lasing mode is demonstrated. The lasing resonant peak shows a continuous redshift of about 0.5 nm and the device also exhibits dynamic switching of its lasing mode. The lasing modulation can be ascribed to temperature-induced reduction of the bandgap. Our work may be of benefit for external optical modulation in future chip-based optoelectronic devices.

Air lasing: Phenomena and mechanisms

Air lasing is a concept that refers to remote no-cavity(mirrorless) optical amplification in ambient air with the air constituents as the gain media. Due to the high potential of air lasing in view of applications in atmospheric sensing, a variety of pumping schemes have been proposed so far for building up population-inverted gain media in air and producing forward and/or backward directional lasing emissions. This review paper presents an overview of recent advances in the experimental observations and physical understanding of air lasing in various pumping schemes of air molecules by intense laser fields. Special emphasis is given to the strong-field-induced N^+2 air lasing, the mechanism of which is currently still in a hot debate.

Effect of spontaneously generated coherence on inversionless lasing gain in an atomic system with Doppler broadening

We have studied the effect of the spontaneously generated coherence （SGC） on gain of lasing without inversion （LWI） in a closed three-level A-type atomic system with Doppler broadening. It is shown that, regardless of the driving and probe fields being co- or counter-propagating, at a suitable value of the Doppler width, we can obtain a much larger LWI gain with SGC than that without SGC; and the region of the LWI gain spectrum with SGC is obviously larger than that without SGC. When the Doppler width takes a constant value, the gain does not monotonically decrease or increase with increasing strength of SGC, the largest LWI gain can be obtained by adjusting strength of SGC. Generally speaking, the co-propagating probe and driving fields is favourable to obtain a larger LWI gain.

Polariton lasing in InGaN quantum wells at room temperature

In this paper,we report the exciton polaritons in both positive and negative detuning micro cavities based on InGaN multi-quantum wells(MQWs)and the first polariton lasing in InGaN/GaN MQWs at room temperature by utilizing a 4.5λFabry-Perot(F-P)cavity with double dielectric distributed Bragg reflectors(DBRs).Double thresholds corresponding respectively to polariton lasing and photonic lasing are observed along with half-width narrowing and peak blue-shifts.The threshold of polariton lasing is about half of the threshold of photonic lasing.Our results paved a substantial way for ultra-low threshold lasers and room temperature Bose-Einstein Condensate(BEC)in nitride semiconductors.

Raman lasing and other nonlinear effects based on ultrahigh-Q CaF_(2)optical resonator

The calcium fluoride(CaF_(2))whispering gallery mode crystalline resonator is an excellent platform for nonlinear optical applications because of the decreasing in threshold caused by ultrahigh quality(Q)factor.In this paper,we achieved the observation of Raman lasing,first-order Raman comb,and second-order Raman lasing in a CaF_(2)disk resonator with a diameter of 4.96 mm and an ultrahigh-Q of 8.43×10^(8)at 1550-nm wavelength.We also observed thermal effects in CaF_(2)disk resonator,and the threshold of thermo-optical oscillation is approximately coincident with Raman lasing,since the intracavity power increases rapidly when the power reaches the threshold,and higher input pump power results in longer thermal drift and higher Raman emission power.With a further increase in pump power,the optical frequency combs range is from 1520 nm to 1650 nm,with a wavelength interval of 4×FSR.It is a promising candidate for optical communication,biological environment monitoring,spectral analysis,and microwave signal sources.

Observation of the optical X2Σg+–A2Πu coupling in N2+ lasing induced by intense laser field

We propose a simple pump-coupling-seed scheme to examine the optical X^2Σg^+–A^2Πu coupling in N2^+ lasing. We produce the N2^+ lasing at 391 nm, corresponding to the B^2Σu^+(v = 0)–X^2Σg+(v = 0) transition, by externally seeding the N^2+ gain medium prepared by irradiation of N2 with an intense pump pulse. We then adopt a weak coupling pulse in between the pump and seed pulses, and show that the intensity of the 391-nm lasing can be efficiently modulated by varying the polarization direction of the coupling pulse with respect to that of the pump pulse. It is found that when the polarization directions of the pump and coupling pulses are perpendicular, the 391-nm lasing intensity is more sensitive to the coupling laser energy, which reflects the inherent nature of the perpendicular X^2+Σg^–A^2Πu transition.

PT Symmetry Induced Rings of Lasing Threshold Modes Embedded with Discrete Bound States in the Continuum

It is well known that spatial symmetry in a photonic crystal(PhC)slab is capable of creating bound states in the continuum(BICs),which can be characterized by topological charges of polarization vortices.Here,we show that when a PT-symmetric perturbation is introduced into the PhC slab,a new type of BICs(pt-BICs)will arise from each ordinary BIC together with the creation of rings of lasing threshold modes with pt-BICs embedded in these rings.Different from ordinary BICs,the Q-factor divergence rate of a pt-BIC is reduced and anisotropic in momentum space.Also,pt-BICs can even appear at off-high symmetry lines of the Brillouin zone.The pt-BICs also carry topological charges and can be created or annihilated with the total charge conserved.A unified picture on pt-BICs and the associated lasing threshold modes is given based on the temporal coupled mode theory.Our findings reveal the new physics arising from the interplay between PT symmetry and BIC in PhC slabs.

Bichromatic coherent random lasing from dye-doped polymer stabilized blue phase liquid crystals controlled by pump light polarization

In this paper,we investigate the bichromatic coherent random lasing actions from the dye-doped polymer stabilized blue phase liquid crystals.Two groups of lasing peaks,of which the full widith at half maximum is about 0.3 nm,are clearly observed.The shorter-and longer-wavelength modes are associated with the excitation of the single laser dye（DCM） monomers and dimers respectively.The experimental results show that the competition between the two groups of the lasing peaks can be controlled by varying the polarization of the pump light.When the polarization of the pump light is rotated from 0？to 90？,the intensity of the shorter-wavelength lasing peak group reduces while the intensity of the longer-wavelength lasing peak group increases.In addition,a red shift of the longer-wavelength modes is also observed and the physical mechanisms behind the red-shift phenomenon are discussed.

Large Signal Modulation Characteristics in the Transition Regime for Two-State Lasing Quantum Dot Lasers

Large-signal modulation capability, as an important performance indicator, is directly related to the high-speed optical communication technology involved. We experimentally and theoretically investigate the large-signal modulation characteristics of the simultaneous ground-state （GS） and the excited-state （ES） lasing in InAs/OaAs quantum dot laser diodes. The large-signal modulation capability of total light intensity in the transition regime from OS lasing to two-state lasing is unchanged as the bias-current increases. However, GS and ES large-signal eye diagrams show obvious variations during the transition. Relaxation oscillations and large-signal eye diagrams for OS, ES, and total light intensities are numerically simulated and analyzed in detail by using a rate-equation model. The -ndings show that a complementary relationship between the light intensities for OS and ES lasing exists in both the transition regime and the two-state lasing regime, leading to a much smaller overshooting power and a shorter settling time for the total light intensity. Therefore, the eye diagrams of GS or ES lasing are diffuse whereas those of total light intensity are constant as the bias-current increases in the transition regime.

Lasing dynamics study by femtosecond time-resolved fluorescence non-collinear optical parametric amplification spectroscopy

Femtosecond time-resolved fluorescence non-collinear optical parametric amplification spectroscopy （FNOPAS） is a versatile technique with advantages of high sensitivity, broad detection bandwidth, and intrinsic spectrum correction func- tion. These advantages should benefit the study of coherent emission, such as measurement oflasing dynamics. In this letter, the FNOPAS was used to trace the lasing process in Rhodamine 6G （R6G） solution and organic semiconductor nano-wires. High-quality transient emission spectra and lasing dynamic traces were acquired, which demonstrates the applicability of FNOPAS in the study of lasing dynamics. Our work extends the application scope of the FNOPAS technique.

Lasing properties of a Yb ion in tetragonal LuPO_4 and LuVO_4 isomorphic crystals: A comparative study

A comprehensive investigation is carried out to compare the spectroscopic properties, absorption saturation behaviors and lasing properties of a Yb ion in tetragonal LuPO4 and LuVO4 isomorphic crystals. Significant distinctions are revealed in many aspects of the lasing behavior for the Yb ion doped in the two crystal hosts, and Yb：LuPO_4 proves to be superior to Yb：LuVO4 since it enables efficient laser action to be much more easily achieved. With a 0.6 mm thick crystal plate of Yb：LuPO4, an output power of 3.30 W can be generated with an optical–optical conversion efficiency of 50.8%; whereas with a 2 mm long miniature crystal rod, the output power produced can reach 8.35 W with an optical–optical conversion efficiency of 46.7%.

A Model on Understanding Atomic Coherence in Lasing Without Inversion

A laser model which may operate in the absence of population inversion is proposed.It is found that the realization of lasing without inversion in this model is due to the change of noninversion condition along with the creation of atomic coherence,instead of a coherence-term-induced gain enhancement.

Low-Threshold Surface Plasmon Lasing using the Band Edge Mode in a Bi-Periodic Groove Array

We study surface plasmon lasing based on periodic and bi-periodic groove arrays etched on a silver substrate.It is interesting to find that the bi-periodic structure can open a clear band gap of surface plasmon polaritons near the first Brillouin zone boundary,and thus it is promising to utilize the band edge modes of surface plasmon polaritons.A low threshold for the surface plasmon lasing effect is demonstrated numerically,owing to the low group velocity of the band edge mode,which provides a feasible way to design surface plasmon lasers.

Whispering Gallery Mode Lasing Performance's Evolution of Floating GaN Microdisks Varying with Their Thickness

Optical gain and loss of microcavity greatly affect the quality of lasing,how to improve optical gain and decrease optical loss is of great significance for the preparation of laser.In this study,four types standard microdisks with different thicknesses of 2.2μm,1.9μm,1.7μm,and 1.45μm were fabricated by micromachining technology process to modulate optical gain and loss of microdisk lasing.The whispering gallery mode lasing in the ultraviolet range of Ga N microdisk devices was investigated for these devices in order to clarify the effect of microdisk thickness on device characteristics.The quality factor Q and lasing mode number for different thicknesses are calculated from the stimulated spectra.The lifetimes of the exciton combination properties of the devices were observed using time-resolved PL spectroscopy.The lasing modes are modulated,and the lifetime decreases,while the Q factor of the devices first increases and then decreases with decreasing thickness.All these results are induced by optical gain and loss competition.

Theoretical study on the lasing plasmon of a split ring for label-free detection of single molecules and single nanoparticles

This paper reports the plasmonic lasing of a split ring filled with gain material in water. The lasing mode（1500 nm）is far from the pump mode（980 nm）, which can depress the detection noise from the pump light. The laser intensities of the two modes simultaneously increase by more than 10^3 in amplitude, which can intensify the absorption efficiency of the pumping light and enhance the plasmonic lasing. The plasmonic lasing is a sensitive sensor. When a single protein nanoparticle（n = 1.5, r = 1.25 nm） is trapped in the gap of the split ring, the lasing spectrum moves by 0.031 nm, which is much larger than the detection limit of 10^-5 nm. Moreover, the lasing intensity is also very sensitive to the trapped nanoparticle. It reduces to less than 1/600 when a protein nanoparticle（n = 1.5, r = 1.25 nm） is trapped in the gap.

Strong-Field-Induced N2+ Air Lasing in Nitrogen Glow Discharge Plasma

We investigate N_(2)^(+) air lasing at 391 nm,induced by strong laser fields in a nitrogen glow discharge plasma.We generate forward N_(2)^(+) air lasing on the B^(2)Σ_(u)^(+)(v’=0)-X^(2)Σ_(g)^(+)(v"=0) transition at 391 nm by irradiating an intense 35-fs,800-nm laser in a pure nitrogen gas,finding that the 391-nm lasing quenches when the nitrogen gas is electrically discharged.In contrast,the 391-nm fluorescence measured from the side of the laser beam is strongly enhanced,demonstrating that this discharge promotes the population in the B^(2)Σ_(u)^(+)(v’=0) state.By comparing the lasing and fluorescence spectra of the nitrogen gas obtained in the discharged and laser-induced plasma,we show that the quenching of N_(2)^(+) lasing is caused by the efficient suppression of population inversion between the B^(2)Σ_(u)^(+) and X^(2)Σ_(g)^(+) states of N_(2)^(+),in which a much higher population occurs in the X^(2)Σ_(g)^(+) state in the discharge plasma.Our results clarify the important role of population inversion in generating N_(2)^(+) air lasing,and also indicate the potential for the enhancement of N_(2)^(+) lasing via further manipulation of the population in the X^(2)Σ_(g)^(+) state in the discharged medium.

Nickel-Like Molybdenum and Niobium Soft X-Ray Lasing Driven by 200 ps Laser Pulses with 50 J of Energy

Intense lasing at 18.9 and 20.3nm in nickel-like molybdenum and niobium ions has been observed by using two 200ps laser pulses with total energy of 50 J at 1.053μm from XingGuang II laser facility.Their gain coefficients were measured to be 1.6 and 1.5cm-1,respectively.This shows the possibility of extending Ni-like x-ray lasing in low-Z elements and paves the way towards small scale x-ray lasers for applications at university laboratories.

High Intensity Single-Mode Peak Observed in the Lasing Spectrum of InAs/GaAs Quantum Dot Laser

We report on abnormal lasing spectra of InAs/GaAs quantum dot lasers,where a single-mode peak exists with optical intensity several times larger than that of other modes.The maximum side mode suppression ratio of the single-mode peak is measured to be 10.11 dB at 29℃ with injection current of 413 mA.It is found that the emergence of this abnormal lasing spectrum happens in a certain range of operation temperature and current.The sharp increase in optical intensity of the single-mode peak is closely related to the disappearance of optical lasing modes located at the higher energy side of the enhanced mode.

Temperature-tunable lasing in negative dielectric chiral nematic liquid crystal

In this work, negative dielectric nematic liquid crystal SLC 12V620-400, chiral dopant S811, and laser dye DCM are used to prepare dye-doped chiral nematic liquid crystal laser sample. In order to investigate temperature-tunable lasing in negative dielectric chiral nematic liquid crystal, we measure the transmission and lasing spectrum of this sample. The photonic band gap （PBG） is observed to red shift with its width reducing from 71.2 nm to 40.2 nm, and its short-wavelength band edge moves 55.3 nm while the long-wavelength band edge only moves 24.9 nm. The wavelength of output laser is found to red shift from 614.4 nm at 20 ~C to 662.8 nm at 67 ~C, which is very different from the previous experimental phenomena. The refractive indices, parallel and perpendicular to the director in chiral nematic liquid crystal have different dependencies on temperature. The experiment shows that the pitch of this chiral nematic liquid crystal increases with the increase of temperature. The decrease in the PBG width, different shifts of band edges, and the red shift of laser wavelength are the results of refractive indices change and pitch thermal elongation.

Crystal Structure and Characterization of a Dye with Two-photon Pumped Frequency-upconverted Lasing Properties

The title compound, trans 4 [p (N ethyl N (hydroxyethyl)amino) styryl] N methylpyridinium tetraphenylborate(abbreviated as ESMT, C 46 H 49 N 4OB) crystallizes in a space group P 1 with a =0 983 23(15) nm, b =1 410 73(16) nm, c =1 54 21(12) nm, α=95 252(13)°, β= 91 959(17)°, γ= 107 421(12)°, Z=2, F(000)=712, μ =0 1 mm -1 Mo Kα radiation, R =0 093 8. The result shows that the cation of the molecule almost lies in one plane, the hydroxyethyl group is perpendicular to the plane, the anion takes a slight distorted tetrahedral geometry. Also the thermal stability, two photon fluorescence, two photon pumped lasing property for the title compound were studied.