Search

We present a theoretical and experimental analysis of a mid-infrared wavelength-tunable cascade gain modulation Raman fiber laser. Our simulation model incorporates the Generalized Nonlinear Schrödinger Equation with the fiber Bragg grating transmission functions. Utilizing the pulse tracking method, we investigate and analyze the impact of pump pulse width and Raman gain fiber length on the first and second order Raman laser thresholds. Additionally, we exhibit the evolution process of the pulse and optical spectrum at a constant pump pulse energy. Furthermore, we present the output pulse width and energy, and the Raman laser center wavelength as a function of the pump pulse energy. Subsequently, using the optimal theoretical values of pump pulse width and Raman gain fiber length, we experimentally achieve the gain modulation Raman fiber laser. With a 1990 nm laser pumping, the Raman laser can produce a 2172 nm laser with a pulse width of 1.25 µs and a single pulse energy of approximately 400 nJ. When tuning the pump laser wavelength from 1950 nm to 2030 nm, the gain modulation Raman laser wavelength can vary from 2130 nm to 2215 nm. Importantly, our experimental results closely align with the theoretical predictions. This study provides valuable insights for the investigation of gain modulation Raman fiber lasers.

We report the comparative investigation of fabricating type-II waveguide lasers in Nd:Y3Al5O12 (Nd:YAG) using femtosecond laser pulses at 515 and 1030 nm. We focus on the comparison in track morphologies, modification thresholds, and the overall efficiency of the ultrafast laser inscription (ULI) process in creating these waveguides. For both wavelengths, we demonstrated low propagation losses of 0.2 dB/cm. We achieved the lowest reported lasing threshold of 9 mW in a Nd:YAG waveguide laser. Superior performance was achieved with the 1030-nm ULI source, yielding a slope efficiency over 40% and achieving a lasing threshold at half the value observed for the 515-nm source. [ABSTRACT FROM AUTHOR]

We present a theoretical and experimental analysis of a mid-infrared wavelength-tunable cascade gain modulation Raman fiber laser. Our simulation model incorporates the Generalized Nonlinear Schrödinger Equation with the fiber Bragg grating transmission functions. Utilizing the pulse tracking method, we investigate and analyze the impact of pump pulse width and Raman gain fiber length on the first and second order Raman laser thresholds. Additionally, we exhibit the evolution process of the pulse and optical spectrum at a constant pump pulse energy. Furthermore, we present the output pulse width and energy, and the Raman laser center wavelength as a function of the pump pulse energy. Subsequently, using the optimal theoretical values of pump pulse width and Raman gain fiber length, we experimentally achieve the gain modulation Raman fiber laser. With a 1990 nm laser pumping, the Raman laser can produce a 2172 nm laser with a pulse width of 1.25 µs and a single pulse energy of approximately 400 nJ. When tuning the pump laser wavelength from 1950 nm to 2030 nm, the gain modulation Raman laser wavelength can vary from 2130 nm to 2215 nm. Importantly, our experimental results closely align with the theoretical predictions. This study provides valuable insights for the investigation of gain modulation Raman fiber lasers. [ABSTRACT FROM AUTHOR]

Doped transparent ceramics with high optical quality can serve as materials for photonic applications such as laser gain media. In that regard, transparent polycrystalline alumina has potential for high-power applications due to its excellent physical and chemical properties, combined with unique doping possibilities. However, optical birefringence of Al 2 O 3 crystals make achieving sufficiently high optical transmittance a processing challenge. In the present study, we demonstrated fabrication of highly transparent 0.5 at.% Cr:Al 2 O 3 ceramics by high-pressure spark plasma sintering (HPSPS). The optical properties of these polycrystalline ruby ceramics were analyzed in order to assess possible laser operation (at 694.3 nm). The obtained ceramics exhibit high in-line transmittance (∼72.5 % at 700 nm), equivalent to a scattering coefficient of 2.15 cm−1, and characteristic ruby photoluminescence. The theoretically estimated lasing threshold and percentage of absorbed pump power indicate that such ruby ceramic lasers could operate at reasonable thresholds of 80−225 mW with short lengths of 0.5−5 mm. Thus, HPSPS is a promising method for producing laser-quality doped transparent ceramics for compact laser systems. [ABSTRACT FROM AUTHOR]

Spontaneous photon bursts are observed in the output collected from a mesoscale semiconductor-based laser near the lasing threshold. Their appearance is compared to predictions obtained from Laser Rate Equations and from a Stochastic Laser Simulator. While the latter is capable of predicting the observed large photon bursts, the photon numbers computed by the former produces a noisy trace well below the experimentally detectable limit. We explain the discrepancy between the two approaches on the basis of an incorrect accounting of the onset of stimulated emission by the Rate Equations, which instead are capable of complementing the physical description through topological considerations. [ABSTRACT FROM AUTHOR]

We investigate theoretically the possibilities of simultaneous laser generation in all, closely spaced modes of chirped photonic crystals layer in all visible region of the spectrum both for chirped rugate and chirped stratified photonic crystals. The spectra of reflection, field localization as well as relative photonic density of states and absorption for both rugate and stratified photonic crystals with different chirping parameters, as well as for a Fabry-Perot resonator are computed and compared. It was shown that there are two kinds of modes in chirped photonic crystals: edge modes and bound modes. We also calculated the threshold values for mentioned structures. In addition, we note that with the ability to control the chirp contrast, it becomes possible to obtain a white laser with a simple system on a chip, which can find wide application ranging from miniaturized coherent light source, optical sensing, to visible light communication. • White laser with chirped 1D rugate and stratified photonic crystals was proposed. • The spectra of reflection, field localization as well as relative photonic density of states and absorption are computed. • The threshold values for rugate, stratified photonic crystals, and a Fabry-Perot resonator are calculated. [ABSTRACT FROM AUTHOR]

Abstract A Markov model of semiconductor nanolaser is constructed in order to describe finely the effects of quantum fluctuations in the dynamics of the laser, in particular by considering the transition to lasing. Nanolasers are expected to contain only a small number of emitters, whose semiconductor bands are simulated using true carrier energy states. The model takes into account carrier-carrier interactions in the conduction and valence bands, but the result is a huge Markov chain that is often too demanding for direct Monte-Carlo simulation. We introduce here a technique to split the whole chain into two subchains, one referring to thermalization events within the bands and the other to laser photonic events of interest. The model is applied to the analysis of laser transition and enlightens the coexistence of a pulse regime triggered by the quantum nature of the photon with the birth of the known coherent cw regime. This conclusion is highlighted by calculated time traces. We show that on the ultrasmall scale of nanolasers, we are unable to define perfectly the threshold. Highlights • Nanolaser small sizes require new models accounting for the particle quantizations. • Semiconductor nanolaser are modeled as a continuous time Markov chains. • Time evolution are obtained using exact Monte Carlo algorithms. • The Markov chain is optimized owing to the canonical ensemble. • The new model allows a fine description of the semiconductor laser onset. [ABSTRACT FROM AUTHOR]

Amplified Spontaneous Emission is ubiquitous in systems with optical gain and is responsible for many opportunities and shortcomings. Its role in the progression from the simplest form of thermal radiation (single emitter spontaneous emission) all the way to coherent radiation from inverted systems is still an open question. We critically review observations of photon bursts in micro- and nanolasers, in the perspective of currently used measurement techniques, in relation to threshold-related questions for small devices. Corresponding stochastic predictions are analyzed, and contrasted with burst absence in differential models, in light of general phase space properties. A brief discussion on perspectives is offered in the conclusions.

CsPbX 3 (X = Cl, Br, I) perovskites have emerged as promising candidate lasing materials due to their high optical gain, low defect state density, and high absorption coefficient. Unfortunately, they suffer from poor stability, particularly with respect to temperature, moisture, and light exposure, preventing their use in practical optoelectronic applications, such as for amplified spontaneous emission (ASE) with an ultralow laser threshold. Herein, CsPbBr 3 @MCM-41 molecular sieve (CMM) composites are controllably prepared by different ultrasonication and stirring treatments. In addition, different perovskite concentrations and heat-treatment conditions are also considered to demonstrate the ASE behaviors. In addition, CMM@PS (CMMP) and CMM@AB (CMMA) composites were fabricated successfully by further optimizing the mixing ratio of CMM and the polymer. More excitingly, the stability of the CMM@polymer films with respect to the external environment is greatly improved after the polymer coating. To our surprise, the CMM@ploymer thin films demonstrated ASE at room-temperature, with an ASE threshold as low as 0.136 mJ/cm2 and 0.049 mJ/cm2 for CMMA and CMMP, respectively. These results clearly shed light upon the control and optimization of CsPbBr 3 perovskite composite films, paving the way for their widespread use in optoelectronic applications. • The composite films were prepared by one-step spin coating. • The as-prepared film can effectively avoid the instabilities to water and thermal. • SE of the films can be realized by optimizing the pretreatment conditions. • The threshold of ASE can be as low as 0.136 mJ/cm2. [ABSTRACT FROM AUTHOR]

Random laser actions in a disordered media based on polymethyl methacrylate (PMMA) polymer doped with Rh6G dye and Au nanoparticles have been demonstrated. It was observed that the shape of Au nanoparticles can tune the spectral central position of the random laser action. It was also seen that the shape of Au nanoparticles strongly affects the pump threshold. Comparing nanosphere- and nanorod-based systems, the nanorod-based one exhibited a lower threshold. [ABSTRACT FROM AUTHOR]

It is known (yet often ignored) from quantum mechanical or energetic considerations, that the threshold gain of the quasi-static spaser depends only on the dielectric functions of the metal and the gain material. Here, we derive this result from the purely classical electromagnetic scattering framework. This is of great importance, because electrodynamic modelling is far simpler than quantum mechanical one. The influence of the material dispersion and spaser geometry are clearly separated; the latter influences the threshold gain only indirectly, defining the resonant wavelength. We show that the threshold gain has a minimum as a function of wavelength. A variation of nanoparticle shape, composition, or spasing mode may shift the plasmonic resonance to this optimal wavelength, but it cannot overcome the material-imposed minimal gain. Furthermore, retardation is included straightforwardly into our framework; and the global spectral gain minimum persists beyond the quasi-static limit. We illustrate this with two examples of widely used geometries: Silver spheroids and spherical shells embedded in and filled with gain materials. [ABSTRACT FROM AUTHOR]

For a free-electron laser without inversion (FELWI), estimates of the threshold laser power are found. The interaction induced deviation angle of electrons in the first undulator is found. It is shown that for real beams this angle is less than natural divergence angle of the beam. The large-amplification regime should be used to bring an FELWI above the threshold laser power. [ABSTRACT FROM AUTHOR]

A detailed study is presented on the lasing properties of an erbium-doped photonic crystal fiber (PCF) laser. The effects of the host PCF’s structure and laser parameters on continuous-wave laser emission are analyzed by considering the confinement and overlap of pump and signal fields in the gain medium for varying values of pitch, hole diameter, and doping radius. For analysis, we used a finite-difference mode-calculation algorithm devised with standard population and propagation rate-equation solver. Our analysis, applied to an experimentally realized PCF laser, reproduces the observed/reported data, thereby showing the efficacy of our analysis. Finally, a fiber geometry to realize a laser with threshold as low as 6 mW using a short fiber length of 0.52 m is prescribed. The aim of the design is to greatly reduce splice loss with standard single-mode SM28/G.652 fiber while maintaining the optimum performance. These results are new in PCF laser research and should be useful in realizing high performance PCF-based laser devices. [ABSTRACT FROM PUBLISHER]

A study of the threshold characteristics of quantum-dot (QD) laser diodes shows how inhomogeneous broadening and p-doping influence the QD laser's temperature dependence of threshold To. The analysis includes the additional parameters of homogeneous broadening, quantum state populations, and threshold gain. The results show that while the source of negative T0 can occur due to different effects, the transparency current plays a critical role in both undoped and p-doped QD lasers. Experimental trends of negative To and their dependence on p-doping are replicated in the calculated results. Inhomogeneous broadening is found to play a lesser role to the transparency current in setting T0. Homogeneous broadening is most important for uniform QDs with thermally isolated ground-state transitions. [ABSTRACT FROM AUTHOR]

The high energy loss of heavy ions in matter as well as the small angular scattering makes heavy ion beams an excellent tool to produce almost cylindrical and homogeneously excited volumes in matter. This aspect can be used to pump short wavelength lasers. For the first time, a beam of heavy ions was used to pump a short wavelength gas laser in an experiment performed at the GSI ion accelerator facility in December 2005. In this experiment, thewell-known KrF* excimer laser was pumped with an intense uranium beam. Pulses of an uranium beam compressed down to 110 ns (full width at half maximum) with initial particle energy of 250 MeV per nucleon were stopped inside a gas laser cell. A mixture of an excimer laser premix gas (95.5%Kr + 0.5%F2) and a buffer gas (Ar) in different proportions was used as the laser gas. The maximum beam intensity reached in the experiment was 2.5 × 109 particles per pulse, which resulted in 34 J/g specific energy deposited in the laser gas. The laser effect on the transition at λ 248 nm has been successfully demonstrated by various independent methods. There, the laser threshold was reached with a beam intensity of 1.2 × 109 particles per pulse, and the energy of the laser pulse of about 2 mJ was measured for an ion beam intensity of 2 × 109 particles per pulse. As a next step, it is planned to reduce the laser wavelength down to the vacuum ultraviolet spectral region, and to proceed to the excimer lasers of the pure rare gases. The perspectives for such experiments are discussed and the detailed estimations for Xe and Kr cases are given. We believe that the use of heavy ion beams as a pumping source may lead to new pumping schemes on the higher lying level transitions and considerably shorter wavelengths, which rely on the high cross sections for multiple ionization of the target species. [ABSTRACT FROM AUTHOR]

In this paper, we study, both theoretically and experimentally, the threshold characteristics of a distributed feedback fiber laser that depend on the value of a phase shift introduced into the fiber Bragg grating structure. We show that as the phase shift possesses a noticeable birefringence, the laser oscillates at any phase shift value. We also reveal that the laser threshold is different for the cavity eigen polarizations and depends on the phase shift value. We derive a simple analytical formula to calculate the laser threshold in the case of π phase shift; this formula can be utilized to estimate a minimal threshold value for the laser with certain active fiber and Bragg grating parameters. The developed theory allows us to fairly model the experimentally measured dependence of the laser threshold on induced phase shift value. [ABSTRACT FROM AUTHOR]

A high-power and widely tunable all-fiber Raman laser is demonstrated. The Raman fiber laser has been tuned over a range of 60 nm from 1075 to 1135 nm and delivers up to 5.0 W of Stokes output power for 6.5 W of launched pump power. Efficiencies ranging from 76.1 to 93.1% and laser thresholds from 0.78 to 2.59 W have been measured. The spectrum of the depolarized Raman gain coefficient of the germanosilicate fiber has also been inferred from our experimental measurements. [ABSTRACT FROM PUBLISHER]

We investigate the impact of induced absorption caused by injected charge carriers and excited states on the threshold current density of an organic laser diode using numerical simulations. The electrical properties of the device are described by a self consistent drift-diffusion model. The optical properties are calculated using a transfer matrix method. Nonradiative annihilation processes are included employing typical rate constants. In our approach, a three-layer double-heterostructure (DII) with typical organic material properties is studied, which exhibits a threshold current density of 564 A/cm2 - For this virtual device, upper limits for the charge carrier and triplet-triplet absorption cross section σcarrier = 1.53 x 10-3 · σSE and σT1TN = 4.34 x 10-3 · σSE have been calculated as a function of the stimulated emission cross section σSE. Additionally, the role of device geometry, and material properties concerning induced absorptions is studied. It is shown that the impact of absorption processes is not strongly influenced by the device geometry. By increasing the charge carrier mobilities to μ = 2 cm2/V · s in the transport layers and μ = 0.2 cm2/V · s in the emission layer, the impact of polaron absorption can be greatly reduced. In this case, laser operation might still be possible if σcarrier and σSE are within the same order of magnitude. Decreasing the triplet lifetime TT1 is a promising way to reduce the impact of triplet-triplet absorption. For σT1TN and σSE being within the same order of magnitude, the triplet lifetime TT1 has to be reduced to 1 ns for laser operation. [ABSTRACT FROM AUTHOR]

Optical properties and structure of antireflective coatings (AR) deposited from hydrolysed TEOS sol have been characterized in detail. The influence of various parameters on the formation of colloidal silica antireflective coatings by the dip-coating technique has been investigated. For the characterization of colloidal silica films, the UV-visible spectroscopy, laser ellipsometry, and atomic force microscopy were used. Using optimal sol-gel processing conditions (dipping rate -- 40 mm/min, coating time -- 20 s, and temperature -- 20 °C), the colloidal silica coatings were obtained and characterized in comparison with non-coated glass substrate. The reflectance of AR coatings increased with increasing the temperature of sol-gel processing. The laser damage threshold of as deposited films was measured at 1064 nm (1H) and 33.5 nm (3H) wavelength using a Nd:YAG lasers. The laser damage threshold of AR coating exceeded 15.22 J/cm² at 1064 nm and 26.82 J/cm² at 355nm. [ABSTRACT FROM AUTHOR]

Abstract: In December 2005 the first successful operation of a UV excimer laser pumped with a heavy ion beam was demonstrated at GSI. It was the first experiment in which the specific power deposition was sufficient to overcome laser threshold for a UV excimer scheme. The well known excimer laser line at has been chosen for this experiment, because the wavelength is short, but still in the range of usual optical diagnostic tools and the emitted light can propagate in air without attenuation. A bunch compressed beam with a particle energy of and about 110ns pulse duration (FWHM) was used for this experiment. Single pulses of a beam intensity up to particles per bunch were focused into the laser cell along the cavity axis. Compact spectrometers, high speed UV-photodiodes and gated CCD-cameras were used for diagnostics of the spontaneous and stimulated emission. As a main result of the experiment laser effect on the 248nm excimer laser line has been obtained and verified by temporal and spectral narrowing of the laser line as well as the threshold behaviour and exponential growth of intensity with increasing pumping power. In summary it could be shown that the pumping power of the heavy ion beam at GSI is now sufficient to pump short wavelength lasers. It is planned to extend laser experiments in near future to the VUV range of the spectrum . [Copyright &y& Elsevier]

This paper presents a model describing self-mode locking (SML) and sustained self-pulsing (SSP) in a unidirectional ring-fiber laser using only the interaction between the saturated population inversion and the optical signal circulating in the laser cavity. Gain saturation alone is used to explain SML behavior close to laser threshold and the sharp transition to an SSP regime. The model also describes self-pulsing inhibition to the profit of SML for a sufficiently high pump power. Experimental results agree with most model predictions, but the overestimation of the self-pulsing threshold suggests that the phenomenon is furthered by an effect other than gain saturation. [ABSTRACT FROM PUBLISHER]

In this paper, bidirectional (mutual) injection locking is demonstrated with solid-state lasers, producing significant improvements over traditional single-direction injection locking. Each laser element shares part of its output with other elements in bidirectional locking, distinct from single-direction (traditional) injection locking where one master laser provides the locking signal for a number of slaves. In a phase-locked array, the individual laser outputs add coherently, and the brightness of the entire array scales with the square of the number of elements, as if the active material diameter were increasing. Benefits of bidirectional locking, when compared to traditional injection locking, include reduced laser threshold, better output beam quality, and improved scaling capability. Experiments using two Nd:YVO4 lasers confirmed that mutual injection locking reduced lasing threshold by a factor of at least two and increased the output beam quality significantly. The injection-locking effects began with 0.03% coupling between lasers and full-phase locking for coupling exceeding 0.5%. The 0.5% requirement for full-phase locking is significantly lower than the requirement for traditional injection locking. The large coupling requirement limits traditional injection-locked arrays to fewer than 20 elements, whereas mutually injection-locked arrays have no such limit. Mutual injection locking of an array of lasers can lead to a new architecture for high-power laser systems. [ABSTRACT FROM PUBLISHER]

In this paper, a model to calculate the modal gain in organic optical amplifiers and the laser threshold power density in organic laser diode structures is presented. We consider a single-layer design to investigate the dependence of the modal gain and threshold power density on electron and hole mobility, injection barriers, the thickness of the active layer, as well as exciton dissociation at the injecting contacts. A figure of merit is introduced to quantify the influence of absorption by polarons in optical amplifiers. We show that equal charge carrier mobilities are of crucial importance to achieve appreciable gain on the order of 1/cm at a power density of P = 50 kW/cm² for the considered poly[2-methoxy, 5-(2'-ethyl-hexyloxy)-1,4-phenylene vinylene] (MEH-PPV)-like model material. Increasing the injection barriers to φb ≈ 0.3 eV decreases the gain marginally but is beneficial in terms of polaron absorption. Regarding modal gain, there is an optimum thickness for the active layer of d ≈ 200 nm, if different devices are compared on the basis of equal power density. We derive power laws for the dependence of modal gain on mobility and power density, which can serve as guidelines for future device design considerations. We determine the maximum allowed polaron absorption cross section δabs relative to the cross section δstim for stimulated emission that may not be exceeded to achieve positive net gain necessary for optical amplification. For the most favorable parameters, δabs has to be at least 20 times smaller than δstim. The dependence of the laser threshold power density on all of the above-mentioned parameters is investigated. We show that, in the optimum case considered, the power density necessary for lasing is 40 times higher than the highest value reported in the literature. [ABSTRACT FROM AUTHOR]