Laser Concept Research Articles

Surface-plasmons lasing in double-graphene-layer structures

We consider the concept of injection terahertz lasers based on double-graphene-layer (double-GL) structures with metal surface-plasmon waveguide and study the conditions of their operation. The laser under consideration exploits the resonant radiative transitions between GLs. This enables the double-GL laser room temperature operation and the possibility of voltage tuning of the emission spectrum. We compare the characteristics of the double-GL lasers with the metal surface-plasmon waveguides with those of such laser with the metal-metal waveguides.

Cool Laser Pulses

AbstractDuring the past decades pulsed laser systems have motivated many novel laser material applications. Nowadays ultrashort pulse (USP) lasers are routinely used for machining and processing high‐tech materials like glass, sapphire or ceramics and allow the production of small and powerful smart phones, high efficient solar cells or medical devices. The next generation USP lasers will focus on smaller system dimensions, a reduced price and shorter pulses to allow for even higher precision and smaller structuring. The article will give an overview of USP laser technology and concepts for future system configurations.

A proposal for a random Raman laser

The concept of a random Raman laser is investigated using a Monte Carlo simulation. Stimulated Raman scattering is taken into account by introducing an interaction between Raman and pump photons. Due to a lack of experimental data on the subject, validation of this model is accomplished via comparison to analytical solutions in the no scattering, no absorption limit. Random Raman lasing is discussed, and several distinctive properties are predicted.

SiGeSn growth studies using reduced pressure chemical vapor deposition towards optoelectronic applications

In this contribution, we propose a laser concept based on a double heterostructure consisting of tensile strained Ge as the active medium and SiGeSn ternaries as cladding layers. Electronic band-structure calculations were used to determine the Si and Sn concentrations yielding a type I heterostructure with appropriate band-offsets (50meV) between strained Ge and SiGeSn. Reduced pressure chemical vapor deposition system was employed to study the laser structure growth. Detailed analyses regarding layer composition, crystal quality, surface morphology and elastic strain are presented. A strong temperature dependence of the Si and Sn incorporation has been obtained, ranging from 4 to 19at.% Si and from 4 to 12at.% Sn (growth temperatures between 350°C and 475°C). The high single crystalline quality and low surface roughness of 0.5–0.75nm demonstrate that our layers are suitable for heterostructure laser fabrication.

The Double-Heterostructure Concept: How It Got Started

The double-heterostructure (DH) concept for lasers and light-emitting diodes (LEDs) grew out of the prelaser context of increasing the speed of the early bipolar junction transistors. The 1954 idea was to change the energy gap itself, with a graded-gap base, or a wide-gap emitter. This led to the 1957 more general concept of quasi-electric fields and potentials in structures with a position-dependent energy gap. This paper gives a personal chronological account of the evolution of these concepts toward the 1963 proposal of the DH laser, including some blind alleys and blunders along the way.

2-µm Tm:Lu₂O₃ ceramic disk laser intracavity-pumped by a semiconductor disk laser.

A proof-of-principle study of a 1.97-µm Tm:Lu2O3 ceramic disk laser, intracavity pumped by a 1.2-µm semiconductor disk laser, is presented. The demonstrated concept allows for improved pump absorption and takes advantage of the broad wavelength coverage provided by semiconductor disk laser technology. For thin disk lasers the small thickness of the gain element typically leads to inefficient pump light absorption. This problem is usually solved by using a complex multi-pass pump arrangement. In this study we address this challenge with a new laser concept of an intracavity pumped ceramic thin disk laser. The output power at 1.97 µm was limited to 250 mW due to heat spreader-less mounting scheme of the ceramic gain disk.

InP-Based Type-II Quantum-Well Lasers and LEDs

Type-II InP-based light sources provide a promising concept for mid-infrared lasers. These have recently made huge progress, as the first electrically and optically pumped lasers could be demonstrated beyond the wavelength limit for type-I InP-based lasers (~2.3 μm). In this paper, we introduce the material system and device concepts, and report the latest achievements, such as electrically pumped lasing operation up to a wavelength of 2.6 μm in pulsed mode, continuous-wave resonant-cavity light-emitting diode operation up to a wavelength of 3.3 μm at 20-80 °C and photoluminescence even up to 3.9 μm.

A Switchable Erbium Doped Fiber Ring Laser System for Temperature Sensors Multiplexing

In this paper, a proof of concept of a switchable erbium-doped fiber ring laser (EDFRL) system that demonstrates temperature sensors multiplexing is carried out showing a high linearity and a sensitivity of 1.55 ${\rm GHz}/^{\circ}{\rm C}$ . The system is based on the detection in the electrical domain of the resulting beat signal of two different laser lines generated by an EDFRL that operates in single longitudinal mode regime (SLM). The SLM operation is achieved by the use of phase shift fiber Bragg gratings with ultranarrow bandwidths of 6 pm. Two independent cavities for the reference signal and sensor signal generation are used to avoid the wavelength competition and to improve the stability. This configuration allows the control of the temperature operation point of the system by adjusting the temperature in the reference side.

Broadly tunable (440–670 nm) solid-state organic laser with disposable capsules

An innovative concept of thin-film organic solid-state laser is proposed, with diffraction-limited output and a broad tuning range covering the visible spectrum under UV optical pumping. The laser beam is tunable over 230 nm, from 440 to 670 nm, with a 3 nm full width at half maximum typical spectral width. The structure consists of a compact fixed bulk optical cavity, a polymeric intracavity etalon for wavelength tuning, as well as five different disposable glass slides coated with a dye-doped polymer film, forming a very simple and low-cost gain medium. The use of interchangeable/disposable “gain capsules” is an alternative solution to photodegradation issues, since gain chips can be replaced without realignment of the cavity. The laser lifetime of a single chip in ambient conditions and without encapsulation was extrapolated to be around 107 pulses at a microjoule energy-per-pulse level.

Proposal for a bosonic cascade laser.

We propose a concept of a quantum cascade laser based on transitions of bosonic quasiparticles (excitons) in a parabolic potential trap in a semiconductor microcavity. This laser would emit terahertz radiation due to bosonic stimulation of excitonic transitions. The dynamics of a bosonic cascade is strongly different from the dynamics of a conventional fermionic cascade laser. We show that populations of excitonic ladders are parity dependent and quantized if the laser operates without an external terahertz cavity.

Superradiant cascade in a seeded free-electron laser.

We report measurements demonstrating the concept of the free-electron laser (FEL) superradiant cascade. Radiation (λ(rad) = 200 nm) at the second harmonic of a short, intense seed laser pulse (λ(seed) = 400 nm) was generated by the cascaded FEL scheme at the transition between the modulator and radiator undulator sections. The superradiance of the ultrashort pulse is confirmed by detailed measurements of the resulting spectral structure, the intensity level of the produced harmonics, and the trend of the energy growth along the undulator. These results are compared to numerical particle simulations using the FEL code GENESIS 1.3 and show a satisfactory agreement.

High power disk laser

The mono-module disk laser concept is an effective design for diode-pumped solid-state lasers, which allows the realization of lasers with super-high output power, having very good efficiency and also excellent beam quality. Since the first demonstration of the principle in 1964 the output power of mono-module disk has been increased to the level of few kW in continuous wave (CW) mode of operation. “Zig-Zag” disk laser geometry does not look like as a perspective one for further output parameters growing. The scaling laws for mono-module disk laser design show that the limits for CW mode of operation are far beyond 100 kW for output power and the energy can be higher than 100 J in pulsed mode of operation. Due to the efficient porous cooling technology and possibility of amplified spontaneous emission (ASE) suppression the operation of the mono-module disk laser geometry is possible in CW and pulse-periodical (P-P) modes at extremely high output power.

Power scaling of fundamental-mode thin-disk lasers using intracavity deformable mirrors

Since its first demonstration almost two decades ago, the concept of the thin-disk laser has proven its excellent power scaling properties, enabling output powers in the multi-kW-range at decent beam quality. However, power scalability in fundamental-mode operation is limited by severe diffraction losses arising from thermally induced aspherical wavefront distortions in the pumped laser crystal. In order to compensate for these wavefront distortions, we have developed a deformable mirror concept based on pneumatic actuation, providing a step-like surface deformation with adaptable magnitude. Using one of these mirrors, we have achieved output powers as high as 815 W at nearly diffraction-limited beam quality (M2<1.4) from a single disk, which is--to the best of the authors' knowledge-the highest output power at this beam quality demonstrated so far.

Low-Power All-Optical Switch Based on Time-Reversed Microring Laser

An all-optical switch based on an absorbing microring resonator laterally coupled to two waveguides is described theoretically using the coupling of modes in time formalism and numerically using the finite-difference time-domain method. The operating principle of the device is based on the recently published time-reversed laser concept. The proposed switch relies on a combination of coherent interference and absorption in the microring and does not require nonlinear refractive index changes. It has a smaller footprint than other approaches, and it is capable of converting frequency- or phase-shift-keyed digital signals to amplitude-shift-keyed signals for direct detection.

High-power diode-pumped solid-state lasers

Diode-pumped solid-state laser technology is reviewed with an emphasis on laser materials and concepts important to high power systems with excellent beam quality. A first principal approach to power scaling is taken in order to summarize and compare the wide variety of laser architectures. Successful approaches are highlighted and directions for future work are discussed.

Principles and performance of tapered fiber lasers: from uniform to flared geometry

We have studied the recently demonstrated concept of fiber lasers based on active tapered double-clad fiber (T-DCF) in copropagating and counterpropagating configurations, both theoretically and experimentally, and compared the performance to fiber lasers based on conventional cylindrical fibers in end-pumped configurations. Specific properties of T-DCFs were considered theoretically using a rate-equation model developed for tapered fibers, and a detailed comparative study was carried out experimentally. Furthermore, we have studied mode coupling effects in long adiabatic tapers due to coiling and local bending. The results allow us to conclude that, with proper fiber design, the T-DCF technology offers a high-potential alternative for bright, cost-effective fiber devices.

Spin-Controlled Vertical-Cavity Surface-Emitting Lasers

We discuss the concept of spin-controlled vertical-cavity surface-emitting lasers (VCSELs) and analyze it with respect to potential room-temperature applications in spin-optoelectronic devices. Spin-optoelectronics is based on the optical selection rules as they provide a direct connection between the spin polarization of the recombining carriers and the circular polarization of the emitted photons. By means of optical excitation and numerical simulations we show that spin-controlled VCSELs promise to have superior properties to conventional devices such as threshold reduction, spin control of the emission, or even much faster dynamics. Possible concepts for room-temperature electrical spin injection without large external magnetic fields are summarized, and the progress on the field of purely electrically pumped spin-VCSELs is reviewed.

A neodymium fluid laser: Laser emission in circulating state

Differing from conventional liquid lasers, a novel concept of fluid laser was provided, which has attractively potential using in high average power lasers. The laser medium was prepared by dispersing Nd3+: phosphate glass micro-balls in organic match liquid. Its optical properties were investigated and the radiative transition rate was calculated by Judd–Ofelt theory. The experiment of laser oscillation in static state indicates that the heat exchanging has limited effect on refractive index of the fluid laser medium in a short time. In circulating state, a laser oscillation occurred at 1058.1nm when pumped by two 808nm diode lasers. The maximum output energy is 2.58mJ with the absorbed pumping energy of 460mJ. This study offers a new way in the exploration of high average power laser.

New concepts of laser in orthodontics

New concepts of laser in orthodontics

High power disk lasers: advantages and prospects

The mono-module disk laser concept is an effective design for diode-pumped solid-state lasers, which allows the realization of lasers with super-high output power, having very good efficiency and also excellent beam quality. Since the first demonstration of the principle in 1966 [1] the output power of mono-module disk has been increased to the level of few kW in continuous wave (CW) mode of operation. ”Zig-Zag” disk laser geometry does not look like as a perspective one for further output parameters growing. The scaling laws for mono-module disk laser design show that the limits for CW mode of operation is far beyond 100 kW for output power and the energy can be higher than 100 J in pulsed mode of operation. Due to the efficient porous cooling technology and possibility of amplified spontaneous emission (ASE) suppression the operation of the mono-module disk laser geometry is possible in CW and pulse-periodical (P-P) modes at extremely high output power.