Особенности одночастотной генерации в квантово-каскадных лазерах спектрального диапазона 7.5-8.0 μm с малой длиной резонатора

The possibility of realizing single-mode emission in quantum-cascade lasers due to modulation of output optical losses in a Fabry-Perot cavity is demonstrated. For the active region of the 7.5–8.0 μm spectral range, two-phonon resonance design we used thus the 50 stages and waveguide layers based on indium phosphide made it possible to realize single-mode lasing at 7.765 μm and at temperature of 292 K. Side-mode suppression ratio was about 24 dB and remained the same with an increase in the current pumping up to 1.2 of the threshold current values. The coefficient of wavelength shift with temperature (temperature tuning) in the single-mode lasing regime was 0.56 nm / K.

Одночастотная генерация арочных квантово-каскадных лазеров при комнатной температуре

Single-mode lasing at room temperature in quantum-cascade lasers (QCLs) with arched cavity design has been demonstrated. The output optical power in single-mode lasing regime at ~7.7-μm lasing wavelength was above 6 mW with a side-mode suppression ratio of up to 25 dB. The QCL heterostructure for the arched cavities was grown by molecular-beam epitaxy (MBE) based on a heterojunction of In_0.53Ga_0.47As/Al_0.48In_0.52As solid alloys, lattice-matched with InP substrate, and InP layers performing the function of waveguide claddings.

Spectral and Spatial Features of Radiation Emitted by a Cholesteric Liquid-Crystal Laser

Spectral and spatial characteristics of radiation emitted by a laser operating on the Bragg structure arising in cholesteric liquid crystals (CLCs) have been studied, as well as their variations with a change of the planar CLC orientation. A defect in the helical structure of the CLC formed by a ternary mixture of cholesterol viscous esters is revealed at the mutually orthogonal orientations of the CLC director at the substrates. This defect manifests itself as a local dip in the selective reflection band, which agrees with the behavior of the defect mode in the photonic crystal. Such a defect in the helical structure stimulates the selection of longitudinal modes with the indices N = ±1, so that the single-mode lasing regime is realized. A spatial ring structure in the laser radiation is found to arise, when higher longitudinal modes are generated.

Spaser as a biological probe

Understanding cell biology greatly benefits from the development of advanced diagnostic probes. Here we introduce a 22-nm spaser (plasmonic nanolaser) with the ability to serve as a super-bright, water-soluble, biocompatible probe capable of generating stimulated emission directly inside living cells and animal tissues. We have demonstrated a lasing regime associated with the formation of a dynamic vapour nanobubble around the spaser that leads to giant spasing with emission intensity and spectral width >100 times brighter and 30-fold narrower, respectively, than for quantum dots. The absorption losses in the spaser enhance its multifunctionality, allowing for nanobubble-amplified photothermal and photoacoustic imaging and therapy. Furthermore, the silica spaser surface has been covalently functionalized with folic acid for molecular targeting of cancer cells. All these properties make a nanobubble spaser a promising multimodal, super-contrast, ultrafast cellular probe with a single-pulse nanosecond excitation for a variety of in vitro and in vivo biomedical applications.

Weak lasing in one-dimensional polariton superlattices

Bosons with finite lifetime exhibit condensation and lasing when their influx exceeds the lasing threshold determined by the dissipative losses. In general, different one-particle states decay differently, and the bosons are usually assumed to condense in the state with the longest lifetime. Interaction between the bosons partially neglected by such an assumption can smear the lasing threshold into a threshold domain—a stable lasing many-body state exists within certain intervals of the bosonic influxes. This recently described weak lasing regime is formed by the spontaneously symmetry breaking and phase-locking self-organization of bosonic modes, which results in an essentially many-body state with a stable balance between gains and losses. Here we report, to our knowledge, the first observation of the weak lasing phase in a one-dimensional condensate of exciton–polaritons subject to a periodic potential. Real and reciprocal space photoluminescence images demonstrate that the spatial period of the condensate is twice as large as the period of the underlying periodic potential. These experiments are realized at room temperature in a ZnO microwire deposited on a silicon grating. The period doubling takes place at a critical pumping power, whereas at a lower power polariton emission images have the same periodicity as the grating.