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Here we describe experimental spin stand measurements as well as simulations of the time constants associated with thermal transients in heat-assisted magnetic recording (HAMR) media. The thermal transients associated with both increasing and decreasing steps in laser power contain at least two time constants each, one on the order of 1 ns and another on the order of 10 ns. These time constants are associated with the central thermal peak in the media and the diffuse thermal background, respectively. In addition, the measured thermal fall time is longer than the thermal rise time due to the disk’s motion relative to the head. Whereas in conventional HAMR a constant laser power is applied during writes, a number of proposed advanced recording schemes use pulsed laser power to improve either recording performance or reliability. The thermal time constants reported here suggest care must be taken when implementing such schemes so that transition locations are not shifted to the detriment of areal density capability. [ABSTRACT FROM AUTHOR]

We report a widely tunable pulsed dysprosium (Dy) -doped fluoride fiber laser within a 545 nm continuous wavelength range around 3 μm, where a home-made random Raman fiber laser (RRFL) at 1.690 μm acts as the pump, and a commercial InAs saturable absorber (SA) is adopted as the Q-switcher. The designed RRFL, excited by a 1.055 μm ytterbium-doped fiber oscillator, can provide the 8th order Stokes emission at 1.690 μm with a high spectral purity of 98.6% and a maximum output power of 14.4 W. Feeding it to a Dy cavity involving an InAs SA and a ruled diffraction grating in a Littrow configuration, stable Q-switching can be initiated and tuned within the continuous/total range of 2.775∼3.320 μm (545 nm)/2.765∼3.338 μm (573 nm), an extension of 50% over the prior 370 nm record [Opt. Lett., vol. 44, no. 9, pp. 2322-2325, 2019], representing the widest level to date from a pulsed rare-earth-doped laser at any wavelengths, to the best of our knowledge. When the wavelength is tuned to 2.992 μm, a maximum average power of 106 mW with 460 ns pulse width, 125 kHz repetition rate, and 0.85 μJ pulse energy is achieved. This work marks the first pulsed Dy-doped fluoride fiber laser pumped at ∼1.7 μm while exhibiting the utility of InAs in pulse generation at the wavelengths of 3∼3.4 μm for the first time, to the best of our knowledge. The demonstration highlights the great potential of ∼1.7 μm pumped Dy-doped fluoride fiber laser as a platform for developing widely tunable pulsed sources in the 3 μm region of the mid-infrared. [ABSTRACT FROM AUTHOR]

A detailed analysis of theexcited state absorption (ESA) transition 4I13/2→4I9/2 which occurs in erbium (Er) doped ZBLAN fiber lasers is performed through numerical modeling. It is found that the ESA plays a significant role in enhancing the 2.8 μm lasing of Er3+ ions. The ESA promotes the ions residing in 4I13/2 (the lower state of the 2.8 μm laser) to 4I9/2, where the ions subsequently decay to 4I11/2 (the upper state of the 2.8 μm laser) rapidly. An energy recycling is consequently realized via the ESA. The ESA can be activated in cascaded 2.8 μm/1.6 μm Er-doped ZBLAN fiber lasers by absorbing the 1.6 μm signal. Through numerical simulation it is found that in cascaded lasers the slope efficiency of the 2.8 μm laser can be elevated to ∼48% with the assistance of the ESA, a value that surpasses the Stokes limit (∼35%) substantially and agrees well with the experimental results previously reported. It is also found that the ESA-induced energy recycling is exothermic, an effect that is non-ignorable in the high-power circumstance. Moreover, the injection of an additional 1.6 μm pump for directly exploiting the 4I13/2→4I9/2 ESA is simulated using the model. It is found that as the second pump is introduced, the 2.8 μm lasing almost entirely relies on the ESA-induced energy recycling, and hence, the laser is capable of operating under very low 976 nm pump power. The simulation results indicate that the 2.8 μm lasing in Er-doped ZBLAN fiber lasers can even be realized using a single 1.6 μm pump, via a combination of the 4I15/2→4I13/2 and 4I13/2→4I9/2 transition. The outcomes of this work can inspire the development of novel, high-performance 2.8 μm Er-doped ZBLAN fiber lasers. [ABSTRACT FROM AUTHOR]

We demonstrated a high-peak-power acousto-optic Q-switched Nd:YAG laser emitting at 1338 nm. The resonator adopted a symmetrical convex-convex cavity with a two-rod configuration, which is side-pumped by a $\mu $ s long pulse laser diode. At the beginning, the free running mode and Q-switched mode operated with single-wavelength emission at 1319 nm and dual-wavelength emission at 1319 and 1338 nm, respectively. By means of using a 8 mm-thick birefringence filter to increase the intra-cavity loss at 1319 nm, single wavelength operation of 1338 nm was achieved with spectral width of 0.31 nm. Under the pump power of 390 W, the Q-switched laser delivers 28.7 W of average output power with an optical conversion efficiency of 7.4%. The pulse width was measured to be 124 ns with a repetition rate of 400 Hz, and the corresponding peak power is up to 0.58 MW. [ABSTRACT FROM AUTHOR]

Extremum-Seeking Control (ESC) is a technique used to stabilize systems to optimal operating conditions. The adjustment of the controller parameters is not usually reported. In this paper we present a computational model for frequency stabilization of a laser source using ESC. The model is based on a saturated absorption spectroscopy experiment used to reference the frequency of the laser light to an atomic transition in Cesium atoms. By using this model, we were able to study the performance and adjust the parameters of the controlled system. This model was succesfully validated using an experimental open loop configuration. The model was then used to predict stable configurations of the controlled system, to be implemented in the experimental setup. As a result, we were able to get the laser frequency locked to a Cs atomic transition in the laboratory with a relative stability in frequency of 6x10-8. [ABSTRACT FROM AUTHOR]

Based on an analysis of kinetic processes in the continuous-wave (CW) single-wavelength two-photon pumped Rb-vapor laser (Rb-TPAL), a three-dimensional computational model is established using the rate equation. Based on the application of the model to cavity-enhanced Rb-TPAL [Yuan et al., Optics Express 29, 4858 (2021)], the calculated and measured dependences of the laser power on the pump power show good agreement. We simulate the Rb-TPAL pumped by a high-power CW laser diode and analyze the effects of temperature, vapor cell length, pump waist, vapor cell transmission, and output mirror reflectance on the characteristics of the blue laser. The results suggest that the output power and efficiency of blue laser can be improved by optimizing the above parameters; however, the particles in the $5^{2}\text{D}_{5/2}$ level face difficulty to transition to the $6^{2}\text{P}_{3/2}$ level, and this limits the further improvement of blue laser efficiency; therefore, an approach is proposed to improve the efficiency of Rb-TPAL. This study can be useful for designing a two-photon pumped alkali metal laser with high-power output. [ABSTRACT FROM AUTHOR]

As a member of the MXene family, tungsten carbide (WC), with its unique physical structure and excellent optical properties, possesses enormous development potentials in ultrafast optoelectronics. In this letter, A WC film saturable absorber (SA) is successfully demonstrated to induce passive Q-switching in an erbium-doped fiber laser (EDFL). The WC nanoparticles (NPs) are synthesized by a hydrothermal method. Stable Q-switched pulses are generated at 1558 nm with a threshold pump power of 141 mW, after inserting the prepared WC film into the EDFL ring cavity. As the pump power ranges from 141 mW to 193 mW, the repetition rate increases from 32.34 kHz to 35.8 kHz, while the pulse duration decreases from $5.5~\mu \text{s}$ to $4.16~\mu \text{s}$. When the pump power reaches a maximum power of 193 mW, the corresponding maximum pulse energy and output power are 81 nJ and 2.9 mW, respectively. To our best knowledge, this is the first report of utilizing WC as SA to achieve Q-switched pulses. Our research results provide a new reference for the realization of pulsed laser using MXene materials and reveal that WC has immense applications in nonlinear optics and ultrafast laser technology, which greatly broadens the frontier of materials for optoelectronic techniques. [ABSTRACT FROM AUTHOR]

In November 2019, the GaoFen‐7(GF‐7) satellite was equipped with China's first laser altimeter with full waveform recording capability, which obtains high‐precision long‐range three‐dimensional coordinates. The influence of clouds is noticeable for laser transmission, and a footprint camera is used to determine laser pointing and to image the ground. However, the cloud inevitably appears in the laser footprint image. In this study, the authors propose a cloud detection scheme for footprint images based on deep learning. First, an adaptive pooling model is proposed according to the characteristics of the cloud region. Next, model fusion was performed based on the SegNet and U‐Net training results. Finally, test time augmentation was used to enhance the data and to improve cloud detection accuracy. The experimental results show that the fusion result of the model was approximately 5% better than that of the traditional cloud detection algorithm, which improved the shortcomings of the traditional algorithm, such as poor detection effect for thin clouds and complex underlying cloud surfaces. The related conclusions have certain reference significance for GF‐7 data processing and related research on footprint images. [ABSTRACT FROM AUTHOR]

In this report we show using numerical simulations that, with judicious choice of pump and fiber parameters, that it is possible to achieve lasing at wavelengths longer than ${4}\,{\mu {\rm m}}$ from the $^6H_{11/2}\rightarrow ^6H_{13/2}$ laser transition of Dy ${^{3+}}$ using an indium fluoride (InF $_3$) glass host. The key issue for this transition is the short lifetime of the upper laser level of ${1.25}\,{\mu {\rm s}}$ relative to the long lifetime of the lower laser level which is ${640}\,{\mu {\rm s}}$. Whilst continuous wave (CW) cascade lasing at ${4.4}\,{\mu {\rm m}}$ and ${3.3}\,{\mu {\rm m}}$ could be achieved, the large pump power requirement at threshold of $>$ 30 W is impractical. Pulsed pumping combined with gain switching, however, offers a viable alternative. We calculate that 200 ns, ${160}\,{\mu {\rm J}}$ pump pulses launched into InF $_3$ fiber could deliver ${15}\,{\mu {\rm J}}$ output at ${4.4}\,{\mu {\rm m}}$. Scaling of average output power is constrained by population buildup in the lower laser level. Boosting the output power by quenching this lower level lifetime using OH $^{-1}$ or Tb ${^{3+}}$ co-dopants are explored as ways to overcome this limitation. [ABSTRACT FROM AUTHOR]

We propose a method to continuously frequency shift a target laser that is frequency stabilized by a reference laser, which is several hundreds of nanometers detuned. We demonstrate the technique using the $\mathrm {5S_{1/2}} \rightarrow \mathrm {5P_{3/2}} \rightarrow \mathrm {29D_{5/2}}$ Rydberg transition in 87Rb vapor and lock the 482 nm target laser to the 780 nm reference laser using the cascaded electromagnetically induced transparency signal. The stabilized frequency of the target laser can be shifted by about 1.6 GHz by phase modulating the reference laser using a waveguide-type electro-optical modulator. This simple method for stable frequency shifting can be used in atomic or molecular physics experiments that require a laser frequency scanning range on the order of several GHz. [ABSTRACT FROM AUTHOR]

Traditionally, spot-positioning algorithms applied in quadrant detector (QD) face some dilemmas, such as blind area between each quadrant, spot shape shift with Gaussian distribution distortion, and also restricted measurement range. In this article, a virtual-movement scheme, which is to build a mapping relationship between spot position and captured luminous energy of photodetectors, based on equations in mathematical physics, is proposed to resolve the above three problems. On the grounds of the proposed scheme, with establishment of spot-trail functions, the actual position of the spot can be obtained by solving the coordinates of intersection point formed by more than one spot virtual-movement trails. Furthermore, a series of novel algorithms capable of theoretically eliminating the errors caused by blind area and Gaussian distribution distortion and maximumly enlarging detecting range is devised. Significantly, the devised algorithms do not have problems of nonlinearity compensation since we do not depend on any fitting method but to solve the exact position of spot centroid. By modifying integral boundaries, the devised algorithms can be applied in any shape of existing 4-QD or promising $n$ -QD. Taking circular and square 4-QDs as two typical examples in this work, the devised algorithms have excellent performances in both types, whether spots near or far away from 4-QD’s center. With an energy-distribution model and the utilization of tolerance zones, wide measurement range and superhigh accuracy are verified both qualitatively and quantitatively. The devised algorithms have also been experimentally demonstrated to work effectively. The proposed scheme is believed to be capable of eliminating the spot-positioning errors in diverse $n$ -QD and provide wide application prospects for different types of quadrant photodetectors used in many cutting-edge areas, including optical manipulation, laser guidance, as well as quantum communication. [ABSTRACT FROM AUTHOR]

An optical setup comprising an external Fabry-Pérot (FP) cavity that maintains ultrashort pulse spatial and temporal coherence, is proposed to generate continuous sub-terahertz repetition rate ultrashort pulses (USP). Analytical results from different sets of pulse-to-pulse carrier-envelop phase offset (Δ &#966CEO) output conditions manifest the possibility to extract and utilize the reflected USP signal from an ultrastable Pound-Drever-Hall phase-locked external FP cavity to stabilize or reset the Δ φCEO to 0 or multiple of 2π rad in real time. The generation of a steady, ultrahigh repetition rate output, from a low repetition rate ultrashort pulse laser requires management of carrier-envelope phase (CEP). The CEP management with the passive external FP cavity group delay dispersion control enables transition from usual quasi- to continuous repetition rate. The net control and management of these parameters allow the passive external FP cavity multiplication factor to be increased above 200. [ABSTRACT FROM AUTHOR]

We demonstrate a direct diode-pumped passively Q-switched (PQS) Tm/Ho composite laser with a developed compact hybrid cavity, where the lasing wavelengths were changeable from Ho laser to Tm laser via decreasing initial transmittance of the crystalline Cr:ZnSe saturable absorbers (SAs) from 95%, 92%, to 89%. Using a common 808 nm diode laser as the pump source, maximum average output power of 390 mW, maximum pulse energy of 39 uJ, and the shortest pulse with a full width at half maximum of 22 ns were obtained at lasing wavelengths of 2122 nm, 2090 nm, and 2011 nm respectively, where these peak wavelengths remained stable during the PQS processes with different SAs. [ABSTRACT FROM AUTHOR]

We successfully demonstrate a blue diode-pumped green single-wavelength self-Q-switched Ho3+:ZrF4-BaF2-LaF3-AlF3-NaF (Ho:ZBLAN) all-fiber laser emitting at ∼550 nm. Such a green laser, being a very simple device, consists of a 15-cm-long Ho:ZBLAN fiber and a pair of fiber input/output mirrors. The Ho:ZBLAN fiber not only acts as a gain medium but also works as a saturable absorber (SA). The modulation mechanism is induced by the ground-state reabsorption effect in an ineffectively pumped section of the active fiber. Stable Q-switching pulses are characterized by a 889 ns of minimum pulse duration and a 264 nJ of maximum energy pulse at a repetition rate of 67.25 kHz. We believe that this work could provide an appreciable alternative for next generation of pulsed green laser source, which finds the applications in the medical diagnosis, optical imaging, and industrial manufacturing. [ABSTRACT FROM AUTHOR]

Mode-locked lasers exhibit complex nonlinear dynamics. Precise observation of these dynamics will aid in the understanding of the underlying physics and provide new insights for laser design and applications. The starting dynamics, from initial noise fluctuations to the mode-locking regime, have previously been observed directly by time-stretched transform-based real-time spectroscopy. However, the regime transition dynamics, which are essential processes in mode-locked lasers, have not yet been resolved because regime transition process tracking is very challenging. Here we demonstrate the real-time observation of the regime transition dynamics enabled by our design of a real-time programmable mode-locked fiber laser, in which different operating regimes can be achieved and switched automatically. The regime transition dynamics among initial noise fluctuations, Q-switching, fundamental mode-locking and harmonic mode-locking regimes have been observed and thoroughly analyzed by both temporal and spectral means. These findings enrich our understanding of the complex dynamics inside mode-locked lasers. [ABSTRACT FROM AUTHOR]

A novel formulation of the set cover problem is presented to find the optimal placement of the scan stations in a terrestrial laser scanning survey. The problem is formulated in 2-D by including sensor-based constraints such as coverage and overlap. The coverage constraint ensures a minimum density of horizontal scan lines on the ground. The overlap constraint enables automatic scan alignment and registration. The optimization problem takes into account both environment occlusions and a maximum allowed incidence angle of the laser beams. The adopted laser model includes fixed parameters such as laser height, angular resolution, field of view, and minimum and maximum sensor range. The sensor placement problem is solved using a numerical approach implemented on graphics processing unit (GPU). Thanks to the GPU acceleration, experiments have been performed in large-scale environments with internal structures. [ABSTRACT FROM AUTHOR]

Transition metal dichalcogenides have recently been considered the candidates for saturable absorption materials due to their advantages in both electronic and optoelectronic. Compared with MoS2 and WS2, MoTe2 exhibits smaller bandgap. As a result, MoTe2 owns inherent advantages in the near-infrared applications. In this paper, the MoTe2 saturable absorber (SA) were prepared by the magnetron sputtering deposition method. Owing to the enhanced light-materials interaction between MoTe2 and evanescent field from the microfiber, the modulation depth of the MoTe2 SA was up to 26.97%. By assembling the MoTe2 SA into the erbium-doped fiber laser, the mode-locked fiber laser at 1.5 μm was demonstrated. The pulse duration of 111.9 fs was proved to be the shortest in the fiber lasers based on transition metal dichalcogenides. Moreover, the mode-locked fiber laser maintains the long-term stability. Our results suggest that the proposed MoTe2 SA is promising for the ultrashort pulse generation and stable system operation. [ABSTRACT FROM AUTHOR]

Highlights • 4F 3/2 → 4I 9/2 laser transition at 928 nm in a Nd:GYTO mixed crystal is realized. • A comparative study of emission was performed under the pump at 808 nm and 879 nm. • Improved performances were achieved under direct pumping into the emitting level. Abstract We report on a 928 nm laser based on quasi-three-level transition of 4F 3/2 → 4I 9/2 in a Nd:Gd 0.69 Y 0.3 TaO 4 mixed single crystal. With LD pumping at 808 nm, an output energy of 29.8 mJ at 928 nm is achieved with an optical-to-optical efficiency of 16.5% and a slope efficiency of 21.2%. In comparison, using 879 nm LD pumping, the maximum output energy at 928 nm reaches 48.5 mJ with an optical-to-optical efficiency of 33.4% and a slope efficiency of 38.0%. [ABSTRACT FROM AUTHOR]

The downtrack thermal gradient (DTTG) is a key metric determining the performance of heat-assisted magnetic recording heads. It describes the change in temperature with respect to the position at the recording point, which determines the transition width and consequently the linear density capability. Here, we present a method for measuring the DTTG by stepping the laser power while writing a series of pseudorandom bit sequences (PRBSs). The sharp change in laser power changes the diameter of the thermal spot produced in the media by the laser and near-field transducer, which in turn produces a shift in the location of the written transitions. The magnitude of this shift is measured from the readback signal and may be used to calculate the thermal gradient. The PRBS-based technique described here has the additional advantage of enabling corrections for a number of errors in the calculation of the thermal gradient, including the nonlinear dependence of the transition shift on the magnitude of the laser power modulation and changes in the curvature due to the change in the size of the thermal spot. [ABSTRACT FROM AUTHOR]

The pointing bias of the laser altimeter would change because of the launch vibration, variations in the space environment or other factors, which is one of the most important factors affecting the geometric accuracy of a laser altimeter. To calibrate pointing bias and improve the measuring accuracy of spaceborne laser altimeter, this paper proposed an in-orbit calibration method based on terrain matching with pyramid-search for this spaceborne laser altimeter. First, we used published digital terrain data as a reference to match with stripes of a point cloud obtained by the geolocation model of the laser altimeter, and then the optimal matching terrain could be determined by a pyramid search. Finally, the pointing bias of the laser altimeter was calibrated. The proposed method was applied in calibration experiment of ZY3-02 laser altimeter. Several tracks of ZY3-02 laser data and advanced Land Observation Satellite Digital Surface Model (AW3D30) with a 30-m grid size were deployed for calibration and validation. After calibration, the systematic error was effectively eliminated. The elevation accuracy of the laser altimeter was improved from more than 100 to 3 m approximately, and the algorithm efficiency with pyramid search was improved by 10 times at least. The experimental result demonstrates that the proposed method is an effective means to calibrate the current spaceborne laser altimeters. [ABSTRACT FROM AUTHOR]

A ternary transitional metal dichalcogenides alloy material, molybdenum sulphoselenide (MoSSe), has been successfully fabricated and used as a saturable absorber (SA) for a passively Q-switched (PQS) Tm:YAP bulk laser operating at $2.0~\mu \text{m}$ for the first time, to best of our knowledge. The open aperture Z-scan method was used to characterize the saturable absorption properties of the prepared MoSSe SA. The maximum average output power and pulse repetition rate, shortest pulse width, highest single pulse energy, and highest pulse peak power of this laser were 2.26 W, 95 kHz, 303 ns, $24.2~\mu \text{J}$ , and 80 W, respectively. The results are distinguished from other two-dimensional materials-based $2.0~\mu \text{m}$ PQS lasers, indicating that MoSSe could be a promising material for generating high power and short pulse width lasers in the $2.0~\mu \text{m}$ spectral range. [ABSTRACT FROM AUTHOR]

This paper numerically investigates the relative intensity noise of quantum dot lasers through a rate equation model taking into account both the spontaneous emission and carrier contributions. In particular, results show that the carrier noise originating from the ground and excited states significantly enhances the relative intensity noise of the laser, while that from the carrier reservoir does not. Simulations also point out that a large energy interval between the quantum confined levels is more suitable for low-intensity noise operation due to the reduced contribution from the carrier noise in the excited state. Finally, the carrier noise is found to have little impact on the frequency noise, thus being negligible for the investigation of the spectral linewidth. Overall, this paper is useful for designing low-noise quantum dot oscillators for high-speed communications, optical frequency combs, and radar applications. [ABSTRACT FROM AUTHOR]

Laser-induced fluorescence diagnostic technique is applied here to probe xenon neutrals and single-charged ions in an ambipolar plasma source. A single tunable diode laser is employed for pumping both following transitions: $6s{~}^{\mathrm {2}} {[{1/2}]}_{\mathrm {1}}^{\mathrm {0}}$ – $6p{~}^{2} {[{3/2}]}_{\mathrm {1}}^{\mathrm {0}}$ (centered at 834.68 nm; air) and $5d{\mathrm {[{4}]}}_{\mathrm {7/2}}$ – $6p{\mathrm {[{3}]}}_{\mathrm {5/2}}$ (centered at 834.72 nm; air), for Xe I and Xe II detection, respectively. The corresponding decay states are $6s{\mathrm {[{3/2}]}}_{\mathrm {1}}^{\mathrm {0}}$ and $6s{\mathrm {[{2}]}}_{\mathrm {3/2}}$ leading to fluorescence signal at 473.415 and 541.915 nm, respectively. A detailed description of the experimental setup along with time-averaged fluorescence signals are presented, demonstrating the possible application of the above adjacent pumping wavelengths in xenon ambipolar plasmas for probing both ions and neutrals under various operating conditions. A comprehensible discussion to what extent the registered laser-induced fluorescence signals mirror velocity distribution functions is realized, following hyperfine splitting and isotopic shift analysis. [ABSTRACT FROM AUTHOR]

Downtrack thermal gradient (DTG) is calculated for heat-assisted magnetic recording (HAMR) systems in both spin-stand experiment and micromagnetic model. DTG is an important parameter in HAMR. It describes the change in temperature in the vicinity of the write position. Recording conditions and media properties affect the switching process, which in turn affects the measured DTG. Trends in DTG versus different recording conditions such as linear velocity and applied field showed very good agreement between experiment and model. The model is also used to quantify the effect on DTG from parameters that are difficult to measure, such as Curie temperature distributions, anisotropy field distributions, and curvature. Finally, a breakdown of the contribution of the different conditions and properties considered on DTG is presented. [ABSTRACT FROM AUTHOR]

In this letter, molybdenum ditelluride (MoTe2), a new member of the transition metal dichalcogenides family, has been characterized and fabricated as an optical modulator for the development of broadband wavelength tunable laser using a Tm3+-doped CaYAlO4crystal as a laser gain medium. The maximum average output power reaches 0.75 W with the shortest pulse width of about $0.69~\mu \text{s}$ and repetition rate of 70.9 kHz, which leads to a pulse energy of about $10.58~\mu \text{J}$ and peak power of 15.3 W. Keeping the MoTe2optical modulator inside the laser resonator and at the same time introducing an undoped YAG for wavelength tuning, wavelength tunable passively Q-switched laser operation with a wavelength range of about 112 nm has been demonstrated. This letter experimentally verifies the potential of the novel 2D material MoTe2as an optical modulator. At the same time, this letter paves the way toward the realizations of simple and compact wavelength tunable pulsed laser sources based on broadband 2D materials saturable absorbers. [ABSTRACT FROM AUTHOR]

We report on the successful laser transfer of biocompatible composite coatings based on polyaniline (PANI) embedded with magnetite (PANI-Fe 3 O 4 ) and Lincomycin hydrochloride (PANI-Lincomycin) or Lincomycin-functionalized magnetite (PANI-Fe 3 O 4 @Lincomycin) by matrix assisted pulsed laser evaporation (MAPLE) technique. The physico-chemical investigations revealed relevant data regarding the stoichiometric deposition, morphology and topography of the as-deposited coatings. Regarding the MAPLE coatings, the FTIR studies evidenced the vibrational bands characteristic to pristine PANI material, while the SEM investigations unveiled a preferential particulate morphology (with aggregates shape and size depending on the deposited material). Additionally, the AFM measurements indicated variations of RMS value, following the Lincomycin and magnetite incorporation. The wettability measurements displayed a hydrophilic behavior of the synthesized coatings, while the electrochemical studies emphasized an enhanced resistance against corrosion in simulated body fluid when compared with bare Ti. Cellular viability, immunofluorescence and SEM results proved that the MAPLE coatings were suitable materials for beneficial adhesion, spreading and proliferation of osteoblast-like cells (MG-63). Moreover, an increased efficiency was evidenced against Staphylococcus aureus biofilm development. The multifunctional properties of the laser processed composite coatings – confirmed by cumulative biocompatible, antimicrobial and anticorrosive behaviors – recommend them as promising solutions for biomedical applications. [ABSTRACT FROM AUTHOR]

Phase engineering of MoS2 transistors has recently been demonstrated and has led to record low contact resistances. The phase patterning of MoS2 flakes with laser radiation has also been realized via spectroscopic methods, which invites the potential of controlling the metallic and semiconducting phases of MoS2 transistors by simple light exposure. Nevertheless, the fabrication and demonstration of laser-patterned MoS2 devices starting from the metallic polymorph have not been demonstrated yet. Here, we study the effects of laser radiation on 1T/1 $\mathrm{T}^{\prime }$ -MoS2 transistors with the prospect of driving an in situ phase transition to the 2H-polymorph through light exposure. We find that although the Raman peaks of 2H-MoS2 become more prominent and the ones from the 1T/1 $\mathrm{T}^{\prime }$ phase fade after the laser exposure, the semiconducting properties of the laser-patterned devices are not fully restored, and the laser treatment ultimately leads to the degradation of the transport channel. [ABSTRACT FROM AUTHOR]

Active optical clocks (AOCs) have the intrinsic suppression of the influence of the cavity’s noise on the output frequency, giving rise to the potentially ultranarrow linewidth. To break the cavity’s thermal noise limitation by taking full advantage of the AOC’s principle, as well as to achieve a long-term instability, we propose a scheme of cavity-stabilized active optical clock. The system consists of two key procedures. The dual-wavelength (DW) output signals share the same cavity and work in the good- and the bad-cavity regime, respectively. Then, the good-cavity signal is locked to a reference cavity by the Pound–Drever–Hall (PDH) technique to stabilize the main-cavity length. By doing this, the main-cavity’s noise is expected to be reduced to the thermal noise floor of the reference cavity. Hence, the frequency stability of the bad-cavity signal will break this noise floor due to the suppression of the cavity-pulling effect. Experimentally, we realize the DW good–bad-cavity laser system by taking the Nd:YAG 1064 nm and Cs 1470 nm transitions as the good- and bad-cavity gain medium. The power and linewidth characteristics of the DW output are studied. Limitation factors of the clock frequency as well as the feasibility of the PDH cavity stabilization are analyzed. [ABSTRACT FROM AUTHOR]

The transmission characteristics of 384 Gbit/s free-space laser link with dense wavelength division multiplexing (DWDM) are demonstrated, with channel spacing of 100 GHz. We use a simulated atmosphere channel with a tunable weak turbulence, and bit error rate (BER) curves of back-to-back transmission, which are measured and contrasted, respectively. To our knowledge, it is the first demonstration in the research of DWDM-DP-QPSK high-speed free-space optical (FSO) transmission in an atmospheric channel with tunable turbulence. For 100 GHz channel spacing, receiving sensitivities can be -33.6, -32.7, and -32.1 dBm for 300, 336, and 384 Gbit/s DWDM-PM-QPSK signals, respectively, at BER of 3.8 _ 10-3 (FEC limit). In comparison with -37.6, -36.1, and -35.1 dBm for B2B case, the power penalties are 4, 3.4, and 3.0 dB, respectively. This study indicates that high-speed coherent DWDM-DP-QPSK FSO transmission is feasible. [ABSTRACT FROM AUTHOR]

We present a method to achieve vector modulation of lightwave using an electroabsorption modulator intregrated laser. The laser section is used for direct phase modulation followed by an amplitude modulation of the electroabsorption modulator section in a cascade manner, which is an alternative method to conventional IQ modulator. To allow an improved phase demodulation, we propose a digital pre-compensation technique for a transmitter in optical coherent system for the first time, which includes a phase-balanced differential phase shift keying encoding and a digital domain pre-equalization filtering. The phase-balanced encoding technique applies parallel DC-balance coding with a phase-balanced symbol mapping, which results in a bounded cumulative phase and a constant statistical characteristic of the modulating signal in differential M-ary phase shift keying and M-ary quadrature amplitude modulation formats. The digital pre-equalization filter also compensates for the phase response of the laser section. Experimental results show that the pre-digital compensation technique allows the improved complex signal demodulation compared to conventional DQPSK modulation in a back-to-back setup. [ABSTRACT FROM AUTHOR]

The optical emission study of aluminum (Al) plasma generated by a $Q$ -switched Nd:YAG laser has been presented. The plasma parameter, such as electron temperature ($T_{e}$) and electron number density ($N_{e}$), has been estimated. The electron temperature has been estimated by four different methods and $N_{e}$ was estimated by Stark broadening of spectral lines and the Saha–Boltzmann equation. The laser-generated Al plasma was optically thin and also fulfills the conditions of local thermodynamical equilibrium. The emission spectrum used for determination of the branching fraction and thus transition probabilities of all allowed transitions. The measured values are good in agreement with the literature. [ABSTRACT FROM AUTHOR]

A parameter is proposed which classifies the laser operating characteristics according to the quasi-level terminology, i.e., as intermediate behavior between that of an ideal two- and three-level or three- and four-level laser scheme. Since the quasi-level parameter is purely based on a generic rate equation description of the laser, no inherent assumptions about gain medium properties or the pumping process are required. The validity of the quasi-level parameter is verified for various prototypical laser schemes. As a specific example of a nonideal laser, the operating behavior of an experimental quantum cascade laser is classified, which constitutes a quite generic laser type since the active region properties can be custom-engineered by quantum design. [ABSTRACT FROM AUTHOR]

All-optical modulation in a quantum cascade laser (QCL) can be rapidly evaluated using a photoluminescence (PL) spectrum. The PL spectrum reflects the electron transition rate of the sub-bands of the active region of a QCL. The peak position, amplitude, and displacement of the PL spectrum can be used to determine the optimal wavelength, spot position, the laser incident angle, optical power, and displacement in the electric field of the near-infrared laser. This PL spectrum approach is rapid, accurate, and simple. Furthermore, it can be used to optimize high-speed all-optical modulation of QCLs for use in free-space optical communication and molecular-detection applications. [ABSTRACT FROM AUTHOR]

Pulse optimization and control are demonstrated in a standard middle-infrared quantum cascade laser by illuminating its front facet with two near-infrared lasers. The 1550- and 850-nm near-infrared lasers are used to optimize the pulse rise/fall time and the pulse shape, respectively, of the quantum cascade laser. Compared with the electric drive, the electron interband transition is directed by the all-optical approach. Simultaneously, the quantum cascade laser’s pulse width, amplitude, and repetition rate are controlled precisely by changing the two near-infrared lasers’ delay time, average power, and repetition rate. Such an all-optical approach is beneficial in the high-speed optimization and control of the quantum cascade laser pulse. It has the potential for application in free-space optical communication and high-speed frequency modulation spectroscopy. [ABSTRACT FROM AUTHOR]

Transparent Nd doped PLZT ceramic was fabricated using uni-axial hot press. Spectroscopic investigation of Nd 3+ (1.0 at%) doped PLZT(8/65/35) ceramic was carried out using Judd–Ofelt theory. Based on this theory the calculated intensity parameters are; Ω 2 = 2.22 × 10 –20 cm 2 , Ω 4 = 1.31 × 10 −20 cm 2 , Ω 6 = 2.32 × 10 –20 cm 2 . These intensity parameters are used to determine the emission probabilities, radiative lifetimes, and branching ratios of the 4 F 3/2 → 4 I J ( J = 9/2, 11/2, 13/2, 15/2) transitions. The calculated radiative lifetime (179 μs) is in good agreement with the measured life time (166 μs). Finally, the emission cross-section of the potential laser transitions was also evaluated. [ABSTRACT FROM AUTHOR]

By considering the spatial motion of the atoms, we study the time evolution of Bell nonlocality and entanglement of a pair of atoms for two kinds of Werner-type internal states in an ideal single-mode ring cavity. We have proved that both Bell nonlocality and entanglement have the phenomena of sudden death and sudden birth for the initial state W ± ′ , while for the initial state W ± , Bell nonlocality has the phenomenon of sudden death, but entanglement decays to zero asymptotically over time. We also notice that the preservation of Bell-inequality violation is much shorter than that of entanglement. In addition, it is shown that the disentanglement time and the Bell-inequality violation time both depend on the purity and the width of the wave packet describing the motion of the atomic center of mass. [ABSTRACT FROM AUTHOR]

Organic solid state lasers are thoughtfully investigated due to their potential applications in communication, sensors, biomedicine, etc. Low amplified spontaneous emission (ASE) excitation threshold value is essential for further use of the material in devices. Intramolecular interaction limits high molecule density load in the matrix. It is the case of the well-known red light emitting laser dye - 4-(dicyanomethylene)-2-methyl-6-(4-dimethylaminostyryl)-4H-pyran ( DCM ). The lowest ASE threshold value of the mentioned laser dye could be obtained within the concentration range between 2 and 4 wt%. At higher concentration threshold energy drastically increases. In this work optical and ASE properties of three original DCM derivatives in poly(N-vinylcarbazole) ( PVK ) at various concentrations will be discussed. One of the derivatives is modified DCM dye in which the methyl substituents in the electron donor part have been replaced with bulky trityloxyethyl groups ( DWK-1 ). These sterically significant functional groups do not influence electron transitions in the dye but prevent aggregation of the molecules. The chemical structure of the second investigated compound is similar to DWK-1 where the methyl group is replaced with the tert-butyl substituent ( DWK-1 T B ). The third derivative ( DWK-2 ) consists of two N,N-di(trityloxyethyl)amino electron donor groups. All results were compared with DCM:PVK system. Photoluminescence quantum yield (PLQY) is up to ten times larger for DWK-1 T B with respect to DCM systems. Bulky trityloxyethyl groups prevent aggregation of the molecules thus decreasing interaction between dyes and amount of non-radiative decays. The red shift of the photoluminescence and amplified spontaneous emission at higher concentrations were observed due to the solid state solvation effect. The increase of the investigated dye density in the matrix with a smaller reduction in PLQY resulted in low ASE threshold energy. The lowest threshold value was obtained around 21 μJ/cm 2 (2.1 kW/cm 2 ) in DWK-1 T B:PVK films. [ABSTRACT FROM AUTHOR]

We analyze the output power versus temperature characteristics of two GaAs/Al0.15Ga0.85As terahertz quantum cascade lasers (THz-QCLs) with maximum operating temperature Tmax=200 and 177 K as well as of one GaAs/Al0.30Ga0.70As THz-QCL with Tmax=150 K and identify the thermally-activated leakage paths responsible for the laser performance degradation as the temperature increases. We identify the specific carrier leakage path active in each THz-QCL structure and are able to reconstruct the output power versus temperature profile over the entire laser operation range. We find that using high barriers in the active region design virtually eliminates carrier leakage from the upper laser level into the continuum, opening a non-radiative scattering path from the upper into the lower laser level parallel to standard electron-LO-phonon emission. This effect, together with the reduced leakage from the lower laser level into the continuum in the high-barrier device, significantly contributes to the Tmax decrease from 177 to 150 K. We further show how electron leakage from the lower laser level into the continuum is enhanced in a GaAs/Al0.15Ga0.85As design with thin barriers, significantly improving the laser performance ( Tmax=200 K). Finally, we propose future design strategies for highly temperature-insensitive THz-QCLs. Our approach offers a straightforward method to analyze and troubleshoot thermally-activated carrier leakage dynamics in THz-QCLs. [ABSTRACT FROM PUBLISHER]

This letter describes the design of a medium infrared laser based on a double clad structure of praseodymium (Pr3+)-doped chalcogenide glass. The overlap of the emission cross sections of Pr3+ in the transitions (3F2, 3H6 $\to $ 3H5, and 3H5 \to $ 3H4) enables both transitions to simultaneously produce a single coherent wavelength in the range between 3.7 and 4.6~\mu \text{m} . A single pair fiber Bragg grating at the overlapping transition wavelengths is used to avoid fabrication complexity of a cascade pumping scheme. In addition, the proposed design takes advantages of the fact that one excited ion will radiate two photons in the overlapping transition wavelengths. In this letter, the laser performance is tested as a function of fiber length, pump power, signal wavelength, fiber background loss, and Pr3+-doped concentration. The modeling results reveal that 48% of slope efficiency could be produced when the fiber losses are about 1 dB/m. [ABSTRACT FROM PUBLISHER]

Specific manifestations of the effect of self-saturation in unidirectional-wave spectroscopy compared with spectroscopy of counterpropagating waves have been identified. The possibility of direct measurement of the rates of the stimulated transfer caused by its own spontaneous emission is shown for spectroscopy of unidirectional waves. [ABSTRACT FROM AUTHOR]

The magnetic field control of spontaneous emission in a four-level atomic system driven by three fields is studied. Using the iterative method, an analytical expression of the spontaneous emission spectrum is obtained. Given that the dipoles of the two transitions from two upper levels to a common lower level are orthogonal, we discuss the influence of the magnetic field which is used to couple the two upper levels on the spontaneous emission spectrum, and find a conversion between destructive and constructive quantum interference by changing Larmor frequency. When introducing the interference between the two transitions, the extremely narrow spectral line is obtained in the emission spectrum, which has a potential application in the high spatial resolution sub-wavelength atom localization. [ABSTRACT FROM AUTHOR]

Neodymium doped phosphate based glasses with composition of (P 2 O 5 + K 2 O + Al 2 O 3 + CaF 2 ) were prepared. The samples were analysed through differential thermal analysis (DTA), Fourier transform infrared (FTIR), absorption, emission and decay measurements. Judd-Ofelt parameters (Ω λ ) have been determined from the spectral intensities of absorption bands in order to calculate the radiative parameters like radiative transition probabilities (A R ), radiative lifetime (τ R ) and branching ratios (β R ) for the 4 F 3/2 → 4 I 11/2 laser transition of Nd 3 + ion. The effective emission bandwidths (Δλ eff ), experimental branching ratios (β exp ) and stimulated emission cross-sections (σ e ) have been determined from the emission spectrum. The decay curves of the 4 F 3/2 level exhibited almost single exponential nature for all the Nd 3 + ion concentrations. [ABSTRACT FROM AUTHOR]

The performance of mid-infrared Er3+-doped fiber lasers has dramatically improved in the last few years. In this paper, we present an overview of the progress in 3.5 \mu \textm fiber lasers based on the dual-wavelength pumping approach. The cross section of the excited state absorption transition used by the 1973  \textnm second pump is found experimentally. A numerical simulation of the expected Q-switched behavior of this fiber laser is presented. This shows that increasing the power of the 977 \textnm pump is important to achieve high-peak power pulses. [ABSTRACT FROM PUBLISHER]

P 2 O 5 PbO Bi 2 O 3 R 2 O 3 (R = Al, Ga, In) glasses doped with Dy 2 O 3 were prepared by melt quenching technique. The prepared glasses were characterized by XRD, optical absorption, FTIR, luminescence studies. Judd-Ofelt parameters have been evaluated for three glass systems from optical absorption spectra and in turn radiative parameters for excited luminescent levels of Dy 3+ ion are also calculated. Emission cross section and branching ratio values are observed to high for 6 H 13/2 level for Dy 3+ ion. The yellow to blue intensity ratios and CIE chromaticity coordinates were calculated. Decay curves exhibit non exponential behavior. Quantum efficiency of prepared glasses was measured by using radiative and calculated life times. IR studies, J-O parameters and Y/B ratio values indicate that more asymmetry around Dy 3+ ions in Ga 2 O 3 mixed glass was observed. Chromaticity coordinates lie near ideal white light region. These coordinates and CCT values have revealed that all the prepared glasses emit quality white light especially the glasses mixed with Ga 2 O 3 are suitable for development of white LEDs. [ABSTRACT FROM AUTHOR]

We report on a quenching behavior of the 3.4~\mu \textm dual-wavelength pumped fiber laser that can be accounted by the adverse contribution from a new excited state absorption transition in Er3+:ZrF4 glasses. The transition occurs between levels 4F9/2 and 4F7/2 and partially overlaps with the 1976 nm pump wavelength. We show that this upconversion process causes strong quenching of the lasing power at 3.4~\mu \textm under insufficient 974 nm pumping. Intracavity fluorescence at 550 nm from levels (2H11/2, 4S3/2) is also monitored as a witness of this excited state absorption mechanism. Through numerical modeling, we estimate the cross section value of the process and show that it is essential to reproduce both power and fluorescence curves. This paper also emphasizes the critical role played by the pump wavelengths. [ABSTRACT FROM AUTHOR]

The laser tracker is widely used in a large component measurement. In practical application, due to the large size and complex shape, the laser tracker relocation is usually performed based on the fiducial points to reduce measurement distance or avoid occlusion. For a conventional relocation method, a lot of fiducial points are expected to be uniformly distributed in the entire measurement volume. However, the number and distribution of fiducial points cannot satisfy this requirement due to the light beam occlusion caused by the measured component and jig, resulting in low relocation accuracy. To solve this problem, we propose a survey adjustment-based relocation method. For this method, first, taking into account the inhomogeneity and anisotropy properties of laser tracker, the weighting matrix related to distance and direction is deduced; second, survey adjustment is performed to reduce the location error of a fiducial point, thereby reducing the relocation error. Simulations and experiments are carried out to verify relocation error, and the results show that compared with a traditional relocation method, our proposed method can achieve higher relocation accuracy only with fewer fiducial points distributed in a narrow space; thus, it can be applied in a complicated environment to solve the light beam occlusion problem. [ABSTRACT FROM AUTHOR]

The edge gradient of the thermal spot used to define bits in heat-assisted magnetic recording is a critical parameter in determining the quality of the magnetic transitions. We review the laser current modulation method used to measure this parameter and introduce the sideband ratio (SBR) approach as a fast, inexpensive technique for getting data on large volumes of heads or media. Mathematical derivation of the SBR method is given along with the details of implementation. Production level data on thousands of recording heads are used to illustrate its usefulness. [ABSTRACT FROM AUTHOR]

We report on experiments on the self-photopumped 3d 1 P 1 →3p 1 P 1 and 4f 1 P 1 →4d 1 P 1 laser transitions in Ne-like and Ni-like ions, respectively. Lasing on the self-photopumped laser line has been observed for the first time for a number of elements including Ne-like V, Cr, Fe, and Co as well as Ni-like Ru and Pd. We have investigated the lasing process by varying the prepulse delay, which shows a shift of the optimum main pulse to second prepulse delays towards lower values with higher atomic number Z. Time-resolved measurements showed that self-photopumped and monopole collision-pumped lasing emission occurs essentially simultaneously. Accurate wavelength measurements and calculations are shown to be in excellent agreement. [ABSTRACT FROM AUTHOR]

More cheap production of boron isotopes is needed to provide further progress in nuclear engineering, microelectronics, and nuclear medicine. Separation of boron isotopes by laser-assisted retarded condensation scheme is considered. Continuous irradiation of steady gas flow is considered. In this case, interaction time of gas flow with laser beam (gas flow length) is desirable to make as long as possible in order to increase excitation probability. It can be provided by suitable choice of gas flow expansion conditions, such as small molar fraction of target gas in carrier gas, gas flow, and ambient small gas pressure and temperature. We propose irradiation cell design as a resonant multipass cavity. In order to estimate its length that can be used for efficient isotopes separation, we calculated laser field distribution inside the cavity for different assumed values for mirror wall reflectivities and average photo-absorption cross sections. It has been shown, that significant saving of electricity (4.2-4.6 times less) can be expected. [ABSTRACT FROM PUBLISHER]