Laser Pump Power Research Articles

Generation of Microsecond Ytterbium-Doped Fiber Laser Pulses using Bismuth Telluride Thin Film as Saturable Absorber

Bismuth telluride (Bi2Te3), a type of topological insulators, is currently in hot pursuit due to its unique physical properties. Therefore, this paper describes a simple Q-switched Ytterbium-doped fiber laser (YDFL) by using Bi2Te3 thin-film as saturable absorber. The few layers Bi2Te3 film was fabricated using optical deposition technique and subsequently, was used in an all-fiber, YDFL setup. As a result, a self-starting Q-switching pulses were first occurred when the laser pumping power reached 88.6 mW. As the pump power level increased, the observed pulses repetition rates had increased steadily from 17 to 29.63 kHz. Hence, this work demonstrated that Bi2Te3 thin-film can be used to successfully generate Q-switching pulses at 1-micron region and is well suited for many photonic applications operated at this wavelength region.

Performance Evaluation of Hybrid Optical Amplifier for Ultra Dense Wavelength Division Multiplexed Optical Network at Narrow Channel Spacing

Abstract In this paper, a competent flat gain hybrid optical amplifier is proposed with an optimum arrangement of erbium doped fiber amplifier (EDFA) and Raman amplifier. Attempts are made to design a hybrid optical amplifier for100 channels, 10 Gbps super dense wavelength division multiplexed (SDWDM) systems at channel spacing of 0.1 nm. Work capacity of the system was compared on the basis of various parameters, viz., noise figure and gain that determined the performance of the system. The gain spectrum of the hybrid optical amplifier depends upon the parameters viz., laser input power, pump power and pump wavelength of the amplifier. It was found that for wavelength range 1,560.38–1,579.59 nm, a flat gain of 4.34 dB is achieved for input power of −10 dB with noise figure variation of 0.818 dB without using any gain flattering scheme. Being simple and cost effective, this hybrid optical amplifier could be recommended for gain flatness characteristics and acceptable noise figure for dense wavelength multiplexed systems.

Facile precipitation synthesis of green-emitting BaY2F8:Yb3+, Ho3+ upconverting phosphor

Abstract Monoclinic phase of BaY2F8:0.2Yb3+, xHo3+ (x = 0.005, 0.01, 0.02, 0.05 and 0.1 mol) and BaY2F8:yYb3+, 0.02Ho3+ (y = 0.01, 0.02, 0.05, 0.1 and 0.2 mol) phosphors were prepared by a facile precipitation method. Rietveld analysis was employed to carry out the structural refinement. The upconversion (UC) luminescence properties of BaY2F8:Yb3+, Ho3+ phosphor were investigated under near infra-red (NIR) excitation and the influence of dopant concentration on their spectra was also accessed. The possible UC processes and the energy transfer mechanisms between Yb3+ and Ho3+ were discussed on the basis of UC decay curves and the UC spectra obtained from a laser-pump power variation. The thermal stability of the BaY2F8:0.2Yb3+, 0.02Ho3+ phosphor was studied in the range of 30–300 °C. The color coordinates of the phosphor were located in the green region with very high color purity.

Optothermal properties of a converter of laser radiation to the radiation of a high-temperature point source

Laser radiation sources of different wavelengths with a silica fiber output are widely used in engineering (surface clearing and scratching/engraving, and so on) and in medicine (effective low-invasive scalpels for treating various diseases). These applications are based primarily on direct exposure of the object to laser radiation. The properties of a converter of such a laser radiation to the radiation of a point (∼0.5 · 0.5 mm), high-temperature (∼2000 K) source with strongly absorbing coating (SAC) at the distal end of the silica fiber are considered in the presented work. The use of a converter expands the capabilities of laser instruments significantly. The temperature (∼2000 K) of the operating silica fiber tip with SAC at a laser pump power of 3–10 W (λ = 1.47 μm) and its time dependence in air atmosphere, in CO2 gas and in vacuum have been studied in experiment. The results of the studies and the physical properties of heat transfer and material stability in the converter design are considered. Recommendations on converter application as a scalpel with SAC for cutting soft and hard biological tissues are formulated.

Host‐Sensitized Continuum‐Broad‐Band White‐Light Emitting Yb2O3:Er3+ Phosphor under CW‐NIR Light Absorption

AbstractSingle cubic phase Yb2O3:Er3+ phosphors have been synthesized via solid state reaction technique and characterized by X‐ray diffraction (XRD) and Field emission scanning electron microscopy (FE‐SEM) analysis. An unusual continuum broad band white colour upconversion (UC) emission has been observed under 980 nm continuous wave (CW) near infrared (NIR) laser diode excitation. Interestingly, the phosphor shows characteristic erbium ion transitions at low pump power, but at high pump power heat associated continuum broad band emission was realized. The continuum broad band emission was explained on the basis of energy level diagram, laser induced pump power dependence and blackbody radiation theory. The heat associated/incandescence‐like light is originated due to heating induced by the nonradiative relaxation followed by sensitization (Yb → Er) and Yb−Yb dimer formation. The synthesized phosphor emits effective broad band white colour emission under high pump power and colour co‐ordinates (white colour: 0.34, 0.32) were located in the chromaticity diagram. Intrinsic optical bistability (IOB) behavior shows the hysteresis‐like loop originated upon variation in the laser pump power. The observed high temperature at point of irradiation of the prepared nanocrystalline phosphor is about ∼ 2442 K at 1430 mW, which is high as compare to tungsten bulb (2400 K for 100 W). The developed phosphors can be useful in white light production, solar cell efficiency enhancement, switchable bistable and as light to heat converter.

Luminescence study of Si/SiC nano-particles embedded in SiOxCy matrix deposited using O-Cat-CVD

Silicon (Si) and silicon carbide (SiC) nanoparticles embedded in an amorphous matrix of SiOxCy were grown using a very safe and economic precursor, tetra-ethyl orthosilicate (TEOS-(Si(OC2H5)4)) by an organic catalytic chemical vapor deposition technique (O-Cat-CVD) at a relatively low filament temperature of 1700 °C and a substrate temperature of 300 °C. These crystalline nanoparticles were generated during the growth process in the thin film matrix, without the need for any post-annealing treatment. Morphology and crystalline phase identification of the nanoparticles were studied using Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) respectively. X-ray Photoelectron Spectroscopy (XPS) and Fourier transform infrared (FTIR) revealed the presence of Si, O, C presence in the matrix and additionally different bonding peaks such as SiOSi rocking, SiC stretching, SiH bending, SiOH, SiOSi antisymmetric stretching, SiCH3 bending, CC and CH modes confirmed the formation of SiOxCy matrix. Optical studies were carried out using the photoluminescence spectroscopy, and broad, intense visible emission was observed from the sample.Further, investigation of the luminescence mechanism was carried out using the time-resolved photoluminescence (TRPL) and low-temperature photoluminescence (LTPL). The decay time was found in the order of few nanoseconds, which remarked that the emission is mainly from the radiative recombination inside the Si and SiC nanoparticles embedded in SiOxCy matrix and was attributed to the quantum confinement effect (Q.C.E). Additional, measurements were carried out by varying the laser pump power, and two extreme powers (low pump power, 2 mW, and high pump power, 30 mW) were used to find their impact on the emission. As in overall, the emission found in the present study can be used to develop potential applications such as LED, the third generation of solar cells among others.

Active control of photo-induced electromagnetically induced transparency in terahertz region

The characteristic of an all-optical electromagnetically induced transparency (EIT) analogue generated on GaAs substrate in terahertz (THz) region has been investigated. By increasing power of pump laser, a phenomena of EIT analogue emerged. It was found that the resonance frequency as well as the time delay can be dynamic tuned by controlling the power of pump laser, which displayed a blue shift by increasing the conductivity. Furthermore, the coupled Lorentz oscillator model has been used to analyze the physical mechanism of photo-generated EIT analogue as well. This approach may provide a reference for the design of the rapid tuning device.

Comprehensive Study on the Combined Effect of Laser-Induced Heating and Laser Power Dependence on Luminescence Ratiometric Thermometry.

Luminescence ratiometric thermometry, on the basis of nonthermally linked states of lanthanides, became a hot research issue recently because of its several attractive features. Here, the 5F4,5S2/5F5–5I8 transitions of Ho3+ embedded in calcium tungstate host are taken as an example to show the influence of laser pump power on this temperature detection technology. The luminescence intensity ratio between the 5F4,5S2/5F5–5I8 upconversion emission lines was found to respond monotonously to the temperature between 303 and 603 K and could be fitted well with the use of an empirical function. It suggested that this ratio might be suitable for temperature measurement. However, at 303 K, the temperature readout derived from this ratio decreased from 303 to 248 K on increasing the laser pump power from 35 to 205 mW (the irradiated spot’s area: ca. 2 mm2). This uncommon phenomenon differs from the conventional laser-induced heating effect. With the help of the Boltzmann distribution based on the two Stark components of the 5F5 state of Ho3+, the laser-induced heating was calculated to be ca. 20 K when the excitation power was 205 mW. Thus, this suggested that there should be a mechanism responsible for the gradually decreasing temperature readout. It was then confirmed that this mechanism was the different dependences for the 5F4,5S2/5F5–5I8 transitions on laser pump power, which was much stronger than the laser-induced heating effect. A calibration method to eliminate the influence of laser power dependence on luminescence ratiometric thermometry was then proposed.

Thermal Lens Study of NIR Femtosecond Laser-Induced Convection in Alcohols.

We use time-resolved thermal lens (TL) experiments to examine the convective heat transfer at microscale in the first eight members of the homologous series of primary alcohols. TL measurements enable a direct study of these primary alcohols without adding any chromophore as a function of varying heat loads created via femtosecond laser pulses at 1560 nm. Convective heat transfer leads to the asymmetrical and reduced thermal gradient, which substantially weakens the TL signal. The inflection in the time profile of the TL signal of methanol at higher powers is attributed to the greater molecular convection in methanol compared to other samples. This inflection dies out with a decrease in laser power. Our results demonstrate that the convection is more prominent at higher laser powers in all samples, and it modifies the trend in the steady-state TL signal of different alcohols with pump laser power. Methanol also has the highest steady-state TL among the primary alcohol series at low laser powers. The maxima in the TL signal are shifted systematically from methanol to ethanol and then to propanol as the laser power increases. Semiempirical analysis of time-resolved TL signal by using the latest theoretical TL model enabled us to extract the coefficient of convective heat transfer in methanol at different laser powers. In addition to that, analysis of other members of alcohol series at the highest (7.3 mW) laser power shows that convection is more facile in short-chain alcohols compared to the long-chain alcohols.

All-fiber passively Q-switched erbium fiber laser implementing erbium-ytterbium-thulium co-doped saturable absorber fiber

We demonstrate a passive Q-switched fiber laser using an erbium-ytterbium-thulium (Er-Yb-Tm) doped fiber. The length of the Er-Yb-Tm co-doped fiber is varied from 0.4 m to 1.4 m to study the effect of this passive gain medium for pulse laser performance. The proposed laser operates in the pulse operation regime within a certain range of pump powers, which is dependent on the length of the Er-Yb-Tm co-doped fiber. A longer fiber employed in the laser cavity results in a higher laser pump power threshold, but a wider pump power range of pulse laser operation. The experimental outcome shows that a 1.0 m Er-Yb-Tm co-doped fiber offers the best performance in this work with a Q-switched pump power threshold of 45.1 mW, the widest pulse energy output range of 0.0439 μJ from 0.0167 μJ to 0.0606 μJ, with the supplementary advantage of 120.7 mW Q-switched laser operating range. This fiber gain medium analysis contributes to the generation of short pulse laser source without employing any chemical materials and complex laser setup.

Monochromatic NIR UC emission in Tm3+/Yb3+co-doped GdVO4 phosphor: the effect of the Bi3+ ion concentration and pump power of a diode laser.

A Tm3+/Yb3+/Bi3+ co-doped GdVO4 phosphor sample has been synthesized using a high-temperature solid-state reaction technique. The X-ray diffraction patterns reveal pure phase formation and crystalline behavior of the synthesized samples. Intense blue and NIR upconversion emissions have been observed upon excitation with a 980nm diode laser. It is found that the addition of the Bi3+ ion to the phosphor reduces the intensity of blue emission and enhances the NIR emission intensity to the extent that NIR emission is nearly monochromatic [(INIR/IBlue) ∼ 14]. This ratio is further improved up to 70 times (almost monochromatic) by varying the pump power of the diode laser. Thus, this material can be used as a cheap source of monochromatic NIR emission at 800nm for bioimaging.

Evaluating RSOA Performance with Optical Logic Gates at 100 Gbps Data Rate

Abstract All optical logic gates are the key elements of contemporary optical computing unit. For that non-linear attribute of reflective semiconductor optical amplifier (RSOA) is exploited to configure optical logic gates. Accordingly, in the manuscript all optical OR/NOR/Buffer binary logic network for the nonreturn to zero format has been designed. Its operation at 100 Gbps data rate has been successfully realized. For the applied data inputs in nonreturn to zero patterns, their corresponding output waveforms for the stated logic action have been verified. Numerical investigations for the imperative design constraints as data rate, injected power and imperative elements of the semiconductor optical amplifiers (SOAs) pump current, carrier density, active length, confine factor, laser power has been appropriately executed with optimum performance. It has depicted good extinction ratio (>10 dB) performance with confine factor more than 0.2 and higher carrier density of amplifier. Further, it also accomplished, that for the OR, buffer logic execution with lower power of pump laser and for the NOR logic execution higher power laser pump source is required. The proposed design could fulfill need for the impending higher data rate composite optical computing units.

Switching of exciton character in double InGaN/GaN quantum wells

The dependence on exciton density of the interwell coupling scheme in a series of InGaN/GaN symmetrical double quantum wells (DQWs) with varying central barrier width was observed. Continuous-wave photoluminescence (cw-PL) and time-resolved photoluminescence (TRPL), measured at low temperature (6--13 K), allowed us to examine the competition between three optical recombination channels, namely, the recombination of (i) intrawell excitons (DXs), (ii) interwell indirect excitons (IXs), and (iii) presumably coupled well excitons (CWXs), built of electron and hole wave functions that are widely spread over the entire DQW structure. We demonstrate a rather abrupt switching effect that relies on the actual exciton density in the system. In cw-PL experiments as a function of the pumping laser power, this switching is characterized by a threshold laser power density above which we observe (i) a significant change of slope of both the power-dependent blueshift and intensity of the ground-state exciton and (ii) the appearance of higher-energy optical emissions. In TRPL, as the PL intensity decays with time, both these effects are visible but in opposite direction, including the PL intensity transfer from the higher-energy state to the ground state. The observed switching is assigned to a change of the dominant excitonic recombination regime: at low pumping densities the dominant emission arises from the extremely long-lived IX, whereas above threshold the dominant emission corresponds to DXs or CWXs, depending on the barrier width. The threshold power density (or threshold time for TRPL) presents a clearly exponential dependence upon the width of the central barrier, which demonstrates the role of carrier tunneling in the overall switching process. The comparison of IXs in nitride QWs with bias electric-field induced IXs in GaAs/AlGaAs DQWs shows that the spectral blueshifts are a few times larger in the former structures. This enhancement originates from the built-in electric field in group-III nitrides, which has truly microscopic character. Moreover, it is argued that the presence of the potential fluctuations due to alloy disorder and the fluctuations of the coupling barrier width have only a secondary effect on the observed switching.

Tm3+ doped Bi2O3-GeO2 glasses with silver nanoparticles for optical amplifiers in the short-wave-infrared-region

We synthesized the Bi2O3–GeO2 (BGO) glass doped with thulium ions (Tm3+) and investigate the influence of embedded silver nanoparticles (Ag-NPs) on the samples photoluminescence (PL) and on the process of energy transfer (ET) among bismuth ions and Tm3+. The samples were prepared by the melt-quenching method with and without Tm2O3 and/or AgNO3. Under excitation at 808 nm the pure BGO glass presented PL from 1100 to 1500 nm, characteristic of the bismuth ions, Bi+, while the samples with Tm3+ exhibited a strong PL from 1300 to 1600 nm. The Bi+ emission was quenched due to ET from the bismuth centers to the Tm3+ and the emitted intensity at 1470 nm increased by more than 1000% due to the presence of Tm3+. Moreover, the samples with Tm3+ and Ag-NPs presented further PL enhancement of ≈56% at 1470 nm for the samples heat-treated during 2 h. Optical gain measurements using 2 mm thick samples were performed with a probe beam at 1470 nm and the pump beam at 808 nm. A 4.5 dB/cm gain in the presence of Ag-NPs was measured when the pump laser power was 6 W. The Ag-NPs contributed to 500% of gain enhancement. The present results illustrate the appropriateness of the BGO glass with Tm3+ and Ag-NPs for obtaining intense PL and optical amplification in the near-infrared.

Evolution of Complex Pulse-Bunches in a Bound-State Soliton Fiber Laser

The evolution of complex pulse-bunches in a bound-state soliton fiber laser with a MoS2 saturable absorber is observed with increasing pump laser power. The experiment demonstrated that the stable two-soliton bound state with fixed and tight separation was achieved, inducing strong interplay between the two solitons. The fundamental bound-state mode-locking operations were maintained and the pulse train gradually evolved into complex pulse-bunches to balance the accumulated cavity nonlinear effects as the pump power increased. Our results may offer a platform for the commercial development of stable double-pulse laser sources.

Neutralization of negative hydrogen and deuterium ion beams using non-resonance adiabatic photon trap

Experimental results on neutralization of negative ion beams in a photon stripping target are presented. For the energy of beams used in these studies (6–10 keV), the maximum neutralization efficiency is 95%. In contrast with gas or plasma neutralizers, the generation of positive ions from the negative ion beam was negligible. A non-resonance photon trap with highly reflecting mirrors of special shape was used as a stripping target. Due to a special mirror shape, in the process of photons reflections and propagation inside the trap there are some adiabatically conserved invariants that limits the volume accessible for photon motion even if the mirror surface is not closed. This approach makes it possible to overcome limitations typical for the Fabry–Perot cells, which require high radiation quality, high quality of the optical elements, and very high mechanical stability of the cell. The trap was pumped by commercially available fiber laser (λ = 1070 nm, Δλ = 7 nm, P = 2.1 kW) through a small hole in the mirror. The experiments were carried out with H- and D-beams. The observed neutralization efficiency depended mainly on the reflectivity of the mirrors, on defects on their surface, and on the laser pumping power.

Octave-spanning optical frequency comb based on a laser-diode pumped Kerr-lens mode-locked Yb:KYW laser for optical frequency measurement.

We developed an optical frequency comb based on a Yb:KYW laser. Soft-aperture Kerr-lens mode-locking at the cavity transverse-mode degeneration enabled us to generate 360mW from a 750mW pump laser diode. This resulted in spectral broadening over one octave using just a photonic crystal fiber. We achieved a free-running linewidth of 15kHz in the carrier-envelope offset frequency by optimizing the cavity group delay dispersion, crystal position, and pump laser power, which led to a residual phase noise of 0.51rad during phase-locking. We measured the frequency drift of a cavity-stabilized laser for a clock transition in Yb171+.

Optical vortex lasers by the coherent superposition of off-axis multiple-pass transverse modes in an azimuthal symmetry breaking laser resonator

Optical vortex (OV) laser is generated by the superposition of coherently phase-locked off-axis laser beamlets in a nearly semi-spherical optical resonator with intra-cavity azimuthal symmetry breaking (ASB) optics. Due to the ASB, this laser resonator rejects radiation to resonate on-axis but supports off-axis beamlets belonging to the multiple-pass transverse (MPT) modes. These independent off-axis MPT modes, which are experimentally proven to retrace V-shaped paths in the resonator span ring-shaped intensity distribution and are coherently phase-locked to form an OV with a wavefront dislocation mirroring the topological charge (TC) of the ASB optics. Pumped by a conventional diode laser without critical beam shaping, we successfully generate randomly polarized OV having an annular intensity distribution and a positive unit TC of more than 99.9% at a central wavelength of 1064 nm when the power of pump laser goes above 1.52 W. The build-up of the deterministic phase relation among the independent MPT modes is demonstrated by spatial coherence measurement of the laser from a perturbed ASB resonator. This ASB resonator not only provides an easy approach to generate intrinsic vortex laser with power scalability but also serves as an useful platform to shape laser beams structurally, to study the laser dynamics and to combine radiations coherently.

Two-photon upconversion luminescence of CdTe quantum dots in silicate glasses irradiated by an infrared femtosecond laser

CdTe quantum dots (QDs) were home fabricated in silicate glasses through the conventional melt-quenching technique. Raman analysis confirms the formation of CdTe QDs, and the tunable optical absorption and emission properties exhibit a dependence on QD-size. Meanwhile, the luminescence of CdTe QDs in silicate glasses excited by an infrared femtosecond laser was demonstrated to be a two-photon process by measuring the dependence of fluorescence intensity on laser pump power. Two-photon induced luminescence was achieved by both 800 nm and 960 nm femtosecond laser pulses.

High-order coherent communications using mode-locked dark-pulse Kerr combs from microresonators

Microresonator frequency combs harness the nonlinear Kerr effect in an integrated optical cavity to generate a multitude of phase-locked frequency lines. The line spacing can reach values in the order of 100 GHz, making it an attractive multi-wavelength light source for applications in fiber-optic communications. Depending on the dispersion of the microresonator, different physical dynamics have been observed. A recently discovered comb state corresponds to the formation of mode-locked dark pulses in a normal-dispersion microcavity. Such dark-pulse combs are particularly compelling for advanced coherent communications since they display unusually high power-conversion efficiency. Here, we report the first coherent-transmission experiments using 64-quadrature amplitude modulation encoded onto the frequency lines of a dark-pulse comb. The high conversion efficiency of the comb enables transmitted optical signal-to-noise ratios above 33 dB, while maintaining a laser pump power level compatible with state-of-the-art hybrid silicon lasers.