We demonstrated continuous-wave dual-wavelength operation of a Nd:CALGO laser with intracavity conerefringent element. The laser produced conically refracted dual-wavelength radiation output with more than 100 mW of power. Dual-wavelength radiation was generated owing to the broad gain bandwidth of the Nd:CALGO crystal.
A high power conical refraction (CR) laser was demonstrated based on Yb:CALGO laser crystal with a separate intracavity CR element. The CR laser delivered the maximum output power of 6.25 W at 25 W of incident pump power which is the highest output power for the CR lasers to date. The separation of the CR element from the laser gain medium reduced the complexity of laser pumping. The generated CR laser beam exhibited excellent quality with well-resolved concentric rings and the Poggendorff dark ring.
Compact, widely-tunable, continuous-wave (CW) and ultrashort-pulse laser sources in the visible spectral region are extremely valuable in a wide range of cutting-edge applications such as photomedicine, biophotonics and microscopy. The most promising approach to develop a compact, efficient and widely-tunable visible laser source is second harmonic generation (SHG) in a periodically poled nonlinear crystal containing a waveguide, which not only allows highly efficient frequency conversion even at low pump power levels but also offers an order-of-magnitude increase of wavelength range for efficient SHG by the utilization of multi-mode matching technique. In this respect, semiconductor lasers with their small size, high efficiency, reliability, low-cost and wide spectral range coverage are very promising for the realization of tunable visible laser sources. InAs/GaAs quantum-dot (QD) external-cavity diode lasers (ECDLs), owing to the unique features of QDs, are of special interest for that matter. The use of multi-mode matching technique and SHG in periodically-poled potassium titanyl phosphate (PPKTP) waveguides pumped by tunable QD-ECDLs led to the realization of compact, widely-tunable, visible, CW (567.7 - 629.1 nm and 574 – 647 nm) and picosecond-pulse (600 – 627 nm) laser sources. Furthermore, the ability of QD-ECDLs to generate two tunable longitudinal modes simultaneously allowed the demonstration of dual-wavelength SHG (505.4– 537.7nm wavelength region) from diode-pumped PPKTP waveguides. In addition, compact CW white-light and multicolor laser sources were demonstrated by the use of two ECDLs and a PPKTP waveguide. The demonstrated laser sources represent an important step towards the realization of a compact, room-temperature, tunable laser source in the visible spectral region.
We have demonstrated the highest conical refraction (CR) laser output power to date by placing a CR crystal inside of a diode-pumped Nd:YVO laser cavity. The CR crystal did not have a significant influence on laser output power as well as efficiency. The CR laser produced the maximum output power of 3.68 W with the slope efficiency of 42 % and opticalto- optical efficiency of 34 %. Therefore, this approach could be an attractive pathway for further power scaling of the CR lasers.
A conical refraction (CR) laser based on a separate gain medium (Nd:YVO4) and an intracavity CR element (KGW) was demonstrated. The decoupling of the gain and CR media enabled the laser to produce a well-behaved CR laser beam with excellent quality, while reducing the complexity of the pumping scheme. The proposed laser setup has the potential for power scaling using the efficient diode pumping approach and the properties of the generated CR beam are independent from the laser gain medium.
A semiconductor saturable absorber mirror (SESAM) passively mode-locked Alexandrite laser was demonstrated. Using an InP/InGaP quantum-dot saturable absorber mirror, pulse duration of 420 fs at 774 nm was obtained. The laser was pumped at 532 nm and generated 325 mW of average output power in mode-locked regime with a pump power of 7.12 W. To the best of our knowledge, this is the first report of a passively mode-locked Alexandrite laser using SESAM in general and quantum-dot SESAM in particular.
We report on experiments with conical refraction of laser beams possessing a high beam propagation parameter M2. With beam propagation parameter values M2=3 and M2=5, unusual Lloyd’s distributions with correspondingly three and five dark rings were observed. In order to explain this phenomenon, we extend the dual-cone model of the conical refraction that describes it as a product of interference of two cones that converge and diverge behind the exit facet of the crystal. In the extended model, these converging/diverging cones are represented as the cone-shaped quasi-Gaussian beams possessing the M2 parameter of an original beam. In this formalism, a beam-waist of these cone-shaped beams is proportional to the M2 value and defines the area of their interference which is a width of the Lloyd’s ring. Therefore, the number of dark rings in the Lloyd distribution is defined by the M2 value and can be much greater than unity. The results of the numerical simulations within the extended dual-cone model are in excellent agreement with the experiment.
We present our recent results on CW and pulsed THz generation in quantum dot(QD) based photoconductive antennae(PCA) pumped by ultrafast and dual wavelength semiconductor lasers. QDPCA substrate incorporates InAs QDs in GaAs matrix, thus keeping semiconductor carrier mobility at higher levels that is typical for SI GaAs, while QDs themselves serve as lifetime shortening centres, allowing to achieve subpicosecond operation as in LT-GaAs. Thus, such substrates combine the advantages and lacking the disadvantages of GaAs and LT-GaAs, which are the most popular materials so far, and thus can be used for both CW and pulsed THz generation. Moreover, by changing QD size and mutual allocation, effective pump wavelengths can be tuned in the range between 0.9-1.3 μm, which is well beyond the GaAs energies, hence compact and relatively cheap ultrafast and narrow line double-wavelength semiconductor and fibre pump lasers can be used for pumping such antennae for both pulsed and CW THz generation.
For double wavelength operation of semiconductor lasers, we implement either stacked double volume Bragg gratings, or double-Littrow configuration with two independent diffraction gratings to achieve tunability of the generated THz signal. High thermal tolerance of QD wafers allowed pumping single-gapped antennae with lasers producing up to 250 mW of CW optical power at simultaneous double wavelength operation and up to 1W average optical power in pulsed regime.
We show these QD based antennae combined with such pump lasers to generate pulsed and CW THz radiation that is superlinearly proportional to pump power and bias applied to antenna.
Ultrashort laser pulses from vertical-external-cavity surface-emitting lasers (VECSELs) have been receiving much attention in the semiconductor laser community since the first demonstration of sub-ps-pulsed devices more than a decade ago. Originally relying on semiconductor saturable-absorber mirrors for pulse formation, mode-locked operation has not only become accessible by using a variety of saturable absorbers, but also by using a saturable-absorber-free technique referred to as self-mode-locking (SML). Here, we highlight achievements in the field of SML-VECSELs with quantum-well and quantum-dot gain chips, and study the influence of a few VECSEL parameters on the assumed nonlinear lensing behavior in the system.
Two blue (450 nm) light–emitting diodes (LED), which only differ in top p-GaN layer growth conditions, were
comparatively investigated. I-V, C-V, TLM, Electroluminescence (EL) and Photoluminescence (PL) techniques were
applied to clarify a correlation between MOCVD carrier gas and internal properties. The A-structure grown in the pure
N2 environment demonstrated better parameters than the B-structure grown in the N2/H2 (1:1) gas mixture. The mixed
growth atmosphere leaded to an increase of sheet resistances of p-GaN layer. EL and PL measurements confirmed the
advantage of the pure N2 utilization, and C(VR) measurement pointed the increase of static charge concentration near the
p-GaN interface in the B structure.
Vertical-external-cavity surface-emitting lasers (VECSELs) have proved to be versatile lasers which allow for various emission schemes which on the one hand include remarkably high-power multi-mode or single-frequency continuouswave operation, and on the other hand two-color as well as mode-locked emission. Particularly, the combination of semiconductor gain medium and external cavity provides a unique access to high-brightness output, a high beam quality and wavelength flexibility. Moreover, the exploitation of intra-cavity frequency conversion further extends the achievable radiation wavelength, spanning a spectral range from the UV to the THz. In this work, recent advances in the field of VECSELs are summarized and the demonstration of self-mode-locking (SML) VECSELs with sub-ps pulses is highlighted. Thereby, we present studies which were not only performed for a quantum-well-based VECSEL, but also for a quantum-dot VECSEL.
Tunable continuous wave (CW) green light generation between 517 nm and 538 nm at room-temperature has been
demonstrated from a frequency-doubled broadly tunable quantum well (QW) external-cavity fiber-coupled diode laser
by use of an uncoated periodically poled potassium titanyl phosphate (PPKTP) crystal waveguide crystal. Green light at
530 nm with maximum conversion efficiency of 14.8% and output power of 12.88 mW has been generated using a
PPKTP crystal waveguide with the cross-sectional area of 3x5μm2. The possibility of tunable second harmonic
generation in the PPKTP crystal waveguides with the cross-sectional areas of 4x4μm2 and 2x6μm2 was also investigated.
Orange light with maximum conversion efficiency exceeding 10% and CW output power of 12.04 mW, 10.45 mW and 6.24 mW has been generated at 606, 608, and 611 nm, respectively, from a frequency-doubled InAs/GaAs quantum-dot external-cavity diode laser by use of a periodically-poled KTP waveguides with different cross-sectional areas. The wider waveguide with the cross-sectional area of 4×4 μm2 demonstrated better results in comparison with the narrower waveguides (3×5 μm2 and 2×6 μm2) which corresponded to lower coupling efficiency. Additional tuning of second harmonic light (between 606 and 614 nm) with similar conversion efficiency was possible by changing the crystal temperature.
We demonstrate a compact all-room-temperature picosecond laser source broadly tunable in the visible spectral region between 600 nm and 627 nm. The tunable radiation is obtained by frequency-doubling of a tunable quantum-dot external-cavity mode-locked laser in a periodically-poled KTP multimode waveguide. In this case, utilization of a significant difference in the effective refractive indices of the high- and low-order modes enables to match the period of poling in a very broad wavelength range. The maximum achieved second harmonic output peak power is 3.25 mW at 613 nm for 71.43 mW of launched pump peak power at 1226 nm, resulting in conversion efficiency of 4.55%.
The devising of a general engineering theory of multifunctional diagnostic systems for non-invasive medical
spectrophotometry is an important and promising direction of modern biomedical engineering. We aim in this study to
formalize in scientific engineering terms objectives for multifunctional laser non-invasive diagnostic system (MLNDS).
The structure-functional model as well as a task-function of generalized MLNDS was formulated and developed. The
key role of the system software for MLNDS general architecture at steps of ideological-technical designing has been
proved. The basic principles of block-modules composition of MLNDS hardware are suggested as well.
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