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Bias current and temperature dependence of polarization dynamics in spin-lasers with electrically tunable birefringence
摘要： We investigate and compare the intensity and polarization dynamics in a vertical-cavity surface-emitting laser (VCSEL) with a monolithically integrated, electrically controlled birefringence tuning mechanism. The influence of the bias current on the polarization dynamics is investigated over a large range of birefringence values. Bias current tuning toward low values and simultaneous maximization of the resonance frequency is an important strategy to optimize the spin-VCSEL toward energy-efficient operation. A polarization dynamics resonance tuning range from a few GHz up to the maximum frequency of 36 GHz was achieved, and polarization dynamics at maximum frequency are demonstrated at minimum bias current and at high temperatures of approximately 70 ○C. We propose a strategy for data communication with low energy consumption and low cooling effort.
关键词： energy-efficient operation,spin-lasers,birefringence,VCSEL,polarization dynamics
更新于2025-09-23 15:19:57
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Study of pulsed laser beams and magnetic field on radish seeds
摘要： In this work we report a study on the in?uence of innovative pulsed stresses utilizing an UV laser and a homemade generator of magnetic ?eld on radish seeds (Raphanus sativus L.) growth. We analysed the seed germination and seedling growth. The UV pulsed laser was an excimer KrF operating at 248 nm, 23 ns of pulse duration, with a laser ?uence of about 40 mJ/cm2. The generator of pulsed magnetic ?eld was realized by the electric discharge on a coil of a high voltage capacitor of 150 μF, 60 kV. The magnetic ?eld pulse waveform exhibited damped oscillations at 215 kHz with a maximum intensity of 400 mT. Groups of uniform radish seeds were exposed to laser pulses at ?ve di?erent doses: 30000 shots (KrF/1), 80000 shots (KrF/2), 145000 shots (KrF/3), 225000 shots (KrF/4) and 275000 shots (KrF/5). Other groups were exposed to magnetic ?eld at eight di?erent doses: 3600 shots (MF/1), 7200 shots (MF/2), 10800 shots (MF/3), 14400 shots (MF/4), 18000 shots (MF/5), 21600 shots (MF/6), 32400 kshots (MF/7) and 36000 shots (MF/8). Simultaneously, untreated seeds were used as control. All treatments were performed at room temperature. Both untreated and treated seeds were transferred in Petri dishes and followed for their germination and seedling growth up to 96 h. The results showed that the stress induced by UV laser photons brought a signi?cant stimulation on root growth which may contribute to improve the performance and the productivity of the plants. On the contrary, all physical stresses induced by magnetic ?elds did not have e?ect on seed germination, as well as on cell elongation growth and on hypocotyls in comparison to control seeds.
关键词： Interaction of radiation with matter,Lasers
更新于2025-09-23 15:19:57
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Mode Locking in Lasers due to Self-Induced Transparency: New Theoretical and Experimental Results
摘要： Recent theoretical and experimental results on coherent passive mode locking in lasers due to self-induced transparency are revised. In contrast to traditional laser systems, where passive mode locking occurs due to the effects of incoherent gain and absorption saturation, this regime of mode locking arises due to coherent interaction between light and matter. Theoretical results are presented that demonstrate the possibility of obtaining single-cycle pulses in a laser with a linear cavity of ultrashort length. Results are also presented from what are apparently the first experiments on coherent mode locking due to self-induced transparency in lasers.
关键词： lasers,single-cycle pulses,self-induced transparency,mode locking,coherent interaction
更新于2025-09-23 15:19:57
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Evaluating the Potential of Laser Beam Quality Improvement by Adaptive Optics System
摘要： AO (adaptive optics) systems have been extensively used to improve the beam quality in high-energy lasers; however, few studies have focused on how much the beam quality could be improved. A novel evaluation criteria and factor is presented in this paper. The factor, defined as power in ring (PIR), is expressed by distinguishing the low- and high-spatial frequency components in the far-field laser intensity distribution. Beams with different PIR values are generated in our model, and then they are compensated by AO systems. Calculation result shows that the PIR factor could evaluate a laser beam’s improvement potential by an AO system quantitatively.
关键词： high-energy lasers,power in ring,adaptive optics,beam quality,spatial frequency
更新于2025-09-23 15:19:57
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Modal instabilities in high power fiber laser oscillators
摘要： Transverse mode competition and instabilities in high-power fiber oscillators have been studied experimentally by monitoring the dynamic power exchanges and characteristic frequencies of the transmitted fundamental mode (FM) and scattered high-order modes (HOMs) of the fiber laser cavity under CW and pulsed pumping. The FM and HOM power evolution indicates the presence of two competing effective laser cavities which result in rich output dynamics and full chaotic operation. The thermal and inversion related contributions to the observed instabilities have been identified by monitoring the associated characteristic instability frequencies under pulsed pumping. It is shown that in the transient regime, both inversion and thermal effects contribute successively to the observed power instabilities. Increasing the pump power leads to full chaotic response through an interplay between transverse and longitudinal mode instabilities.
关键词： Transverse mode instability,inversion effects,thermal effects,high-power fiber lasers,mode competition
更新于2025-09-23 15:19:57
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Effect of cold finger temperature on optical pulse modulation characteristics in a 2.59 terahertz quantum cascade laser
摘要： Terahertz (THz) frequency sources such as quantum cascade lasers (QCLs) offer a variety of new applications in far-infrared frequency bands. For better understanding of their behavior, a device-specific modeling approach is used to predict the optical output power under current modulation and chip temperature. This letter reports the numerical simulation of gain switching to evaluate temperature dependence for short pulse generation in QCLs. Modified rate equations are used for self-consistent computation of emitted THz optical power from QCLs. The device emits at 116 μm and is driven by various inputs such as haversine, tangential hyperbolic and square electrical pulses. From the simulation it is evident that the square input pulse requires the least magnitude current (0.83 A) at 15 K to generate pulses with minimum full width half maximum (FWHM). Moreover, when the peak amplitude of the square input signal is 1.01 A, it generates optical pulses with the least FWHM of 19.42 ps at 45 K. In the case of the haversine input with peak amplitude of 1.8A, a peak power of 27.86 mW is generated at 15 K.
关键词： cold finger temperature,rate equation model,numerical simulation,quantum cascade lasers,full width half maximum,gain switching,optical short pulses
更新于2025-09-23 15:19:57
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Temperature sensor based on IR-laser reduced Graphene Oxide
摘要： A simple, cost-effective approach to realize a sensitive temperature sensor based on IR laser reduced graphene oxide (IRLrGO) is reported. The sensor has been obtained by irradiating a graphene oxide (GO) film, placed between two thin glass substrates, with a continuous wave diode laser operating at 970 nm along its entire length. A conductive strip, 13 mm long, 300 μm wide and 7 μm thick, has been generated by moving the GO film on an X-Y translator stage with a given velocity with respect to the fixed laser fiber tip position. The laser treatment has given rise to the GO reduction confirmed by the resistance R measurements as well as from SEM, EDX, ATR-FTIR and Raman analyses. The temperature dependence of the conductive strip resistance has been measured in air from 30?C to 80?C and in high vacuum from 80 K to 300 K. The sample acts as a sensitive and low mass Resistance Temperature Detector (RTD). Such a sensor is biocompatible and requires a very low bias (<1 V). While the performances of the IRLrGO temperature sensor are stable under high vacuum conditions at room temperature, its behavior remains to be studied when it operates under different environmental conditions.
关键词： Interaction of radiation with matter,Materials for solid-state detectors,Fiber Lasers
更新于2025-09-23 15:19:57
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Universal Output Characteristics of Single-Mode Operation in Low-Loss Large- <i>V</i> -Number Multimode Waveguide Lasers with Transverse Spatial Hole Burning
摘要： We study the performance limit of single-mode operation in low-loss large-V-number planar waveguide lasers, with transverse spatial hole burning as the dominating mechanism for transverse-mode competition. By introducing normalized variables, we develop a simple semianalytical model to describe the universal output characteristics of single-mode emission before the onset of high-order modes, which can be easily scaled to a wide range of laser configuration parameters. Our model is validated using exact numerical solutions, which show applicability beyond that of the low-loss approximation. Our analysis establishes a minimum criterion of the loss ratio between the fundamental and first higher-order mode for a robust single-mode operation. This criterion is much weaker than that of conventional wisdom based on the pure wave-propagation argument, which we attribute to a resonator enhancement effect. Our universal outcome can be denormalized to establish the relationship between single-mode extraction efficiency and optimum output coupling in a multimode laser with arbitrary modal loss ratios over a wide range of single-pass unsaturated gain and loss.
关键词： single-mode operation,transverse spatial hole burning,multimode waveguide lasers,large-V-number,low-loss
更新于2025-09-23 15:19:57
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[Laser Institute of America ICALEO?? 2014: 33rd International Congress on Laser Materials Processing, Laser Microprocessing and Nanomanufacturing - San Diego, California, USA (October 19a??23, 2014)] International Congress on Applications of Lasers & Electro-Optics - Laser ablation cutting of thin silicon subtrates with tunable ultra-short pulsed lasers from 200FS-10PS
摘要： In this paper the influence of the pulse duration in a range of 200 fs up to 10 ps on the cutting process of thin silicon is investigated. The experiments are carried out with a Light Conversion Pharos with various pulse duration between 190 fs and 10 ps. The laser is operated at the second harmonic wavelength of 515 nm and a repetition rate of 200 kHz. Although the ablation threshold, which is determined with the method of Liu [1], amounts 0.27 J/cm2 for 0.2, 1 and 10 ps, one can find extremely different ablation behavior during the cutting experiments. It turns out that independent from pulse energy and pulse overlap the shortest pulse duration at 200 fs leads to a deeper cutting depth and furthermore to a higher cutting speed. This difference can be explained with higher pulse peak intensities and shorter interaction time between laser and material for the 200 fs pulse duration. Nevertheless the general ablation geometry is very similar for all tested pulse durations. We explain this with a simple geometric model. This model considers the projection from a Gaussian beam profile in an existing cutting kerf.
关键词： cutting process,laser ablation,ultra-short pulsed lasers,pulse duration,thin silicon substrates
更新于2025-09-23 15:19:57
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Effect of diode laser application as an adjunct to nonsurgical periodontal therapy on the reduction of red complex microorganisms in type 2 diabetics with chronic periodontitis
摘要： Bactericidal and detoxification effects of diode laser (DL) have been reported in periodontal treatment. The objective of this study was investigating the additional effect of DL with nonsurgical periodontal treatment on the red complex bacteria in type 2 diabetes mellitus (DM) patients with chronic periodontitis (CP). Sixty type 2 DM patients with chronic periodontitis (CP) were randomly assigned in two parallel groups to receive scaling root planning (SRP, n = 30) or SRP followed by DL periodontal pocket irradiation (SRP + DL, n = 30). Recording of clinical parameters and subgingival plaque sampling were performed at baseline, and post therapy (1 and 3 months after treatment). Amounts of Porphyromonas gingivalis, Treponema denticola, and Tannerella forsythia were evaluated with quantitative RT-PCR. Significant reductions for numbers of all three bacterial species were observed at 1 and 3 months compared with baseline for both treatments (p < 0.001), but no significant differences were found between two groups regarding bacterial reductions at these follow-up time points. No additional benefit of DL as an adjunct to nonsurgical periodontal therapy was recognized in the reduction of P. gingivalis, T. denticola, and T. forsythia for type 2 DM patients with CP. Further studies are required to clarify the effects of diode laser on the other periodontopathogens.
关键词： Nonsurgical periodontal treatment,Periodontopathogens,Diabetes mellitus,Diode lasers,Chronic periodontitis
更新于2025-09-23 15:19:57