Laser Level Research Articles

On the Mechanism of Limitation of the Frequency-Energy Characteristics of Metal Vapor Lasers

Electrophysical processes in the discharge circuit of a pulsed metal vapor laser are analyzed. The greatest attention is paid to the initial period of the discharge development and conditions for the inversion formation. It is shown that the limitation of the frequency-energy characteristics (FEC) of lasing is due to the process of populating the metastable levels of metal atoms on the excitation pulse front and redistribution of the rates of population of the laser levels in favor of metastable ones with an increase in the prepulse electron density. Which of the processes plays a decisive role in limitation of the lasing FEC depends on the electrophysical process in the discharge circuit of the laser, the development of which is significantly influenced by the arrangement of electrodes in the gas-discharge tube (GDT). The arrangement of electrodes in the GDT also determines the conditions for the inversion formation and the choice of the optimal pumping parameters. Technical solutions are discussed under which the pumping efficiency of a copper-vapor laser attains ~10%.

Minimize water deficit in wheat crop to ameliorate groundwater decline in rice-wheat cropping system

There is a notion that more withdrawal of groundwater for irrigating the rice crop in rice-wheat cropping system is responsible for water table decline in central Punjab of India. Any reduction in irrigation water by the improved irrigation schedules in rice like alternate wetting and drying, and based on soil moisture potential; shifting planting date, crop diversification of higher irrigation requirement to lower, direct seeded rice, laser levelling etc.; and appropriate tillage system to reduce percolation losses save water and increase water productivity. However, the present study showed that water deficit [evapotranspiration – (rainfall + surface water)] can approximate the water table decline/rise rather than groundwater withdrawal alone. In rice-wheat system though irrigation water requirement of wheat crop is less (300–400 mm) than rice (1500–2000 mm) yet the water deficit, responsible for water table decline, is more in wheat crop than rice. In rice transplanted at recommended time, evapotranspiration (ET) is almost equal to the rainfall, while in wheat ET is 3.9 times that of rainfall. It warrants the ET reduction in wheat, overlooked so far, for supplementary amelioration of water table decline in rice-wheat cropping system. Reduction in ET and saving of energy by different technologies in wheat crop has also been discussed.

Growth, structure and spectroscopic properties of Er,Pr:YAP laser crystal

Er3+ and Pr3+ co-doped YAP laser crystal with high optical quality was grown successfully by the Czochralski method for the first time. By contrast, an Er3+ single doped YAP laser crystal was also grown. The cell parameters of the two crystals were obtained by the X-ray Rietveld refinement method. The X-ray rocking curves indicate that the as-grown crystals possess excellent crystalline quality. The absorption spectra show that the crystals are suitable to be pumped by 972 nm LD. The NIR and MIR emission spectra, the up–conversion spectra and the fluorescence decay curves were also measured to investigate the influence of Pr3+ ions on the spectroscopic properties. The results indicate the Pr3+ ions acting as the deactivator can decrease efficiently the lifetime of the lower laser level 4I13/2 of the Er3+ ions from 10.72 to 0.489 ms, which would be beneficial to decrease the laser threshold and increase the laser conversion efficiency.

Optically Injection‐Locked Mid‐IR Quantum‐Cascade Lasers: The Output‐Power–Modulation‐Bandwidth–Noise Trilogy

AbstractA comprehensive study on the output power, the modulation response, and the relative intensity noise (RIN) behavior of an optically injection‐locked mid‐infrared quantum‐cascade laser reveals that the modulation bandwidth and the output power are enhanced in the stable locking range, while the RIN of the slave laser is a superposition of the master and slave noise sources. Since the RIN level of the master laser can even take the lead, a design procedure is introduced to improve the main characteristics of a free‐running laser, including the RIN, the photon lifetime, the modulation bandwidth, and the bias current, using facet reflectivity tailoring. A figure of merit is defined and the RIN reduction of about 20 dB Hz−1 is obtained for very low injection powers compared with the injection‐locked system before the design of master laser.

Enhanced ~3 μm mid-infrared emissions of Ho3+ via Yb3+ sensitization and Pr3+ deactivation in Lu3Al5O12 crystal

Ho: LuAG, Yb, Ho: LuAG and Yb, Ho, Pr: LuAG laser crystals with high optical quality were successfully grown by the Czochralski method. Compared with Ho: LuAG and Yb, Ho: LuAG crystals, Yb, Ho, Pr: LuAG crystal not only shows a better absorption characteristic but also exhibits weaker ~2 μm emission, as well as superior mid-infrared (MIR) at ~3 μm emission. The ~3 μm MIR emission intensities of Yb, Ho, Pr: LuAG under excitation of a common 970 nm laser diode (LD) is almost nine times that of the Ho: LuAG crystal and twice as much as that of the Yb, Ho: LuAG crystal. The crystal growth, absorption spectra, J-O parameters, emission spectra, fluorescence lifetimes and the energy transfer mechanism in Yb, Ho, Pr: LuAG crystal were studied in this work. The energy transition efficiency from the lower laser level of Ho3+: 5I7 to Pr3+: 3F2 level is as high as 66.6%, indicating that the Pr3+ ion is an effective deactivation ion for Ho3+ ion in Lu3Al5O12 crystal. All these results show that Yb, Ho, Pr: LuAG crystal may become a promising material for developing solid state lasers at around 3 μm under a conventional 970 nm LD pump.

Variability in alignment of central venous pressure transducer to physiologic reference point in the intensive care unit–A descriptive and correlational study

BackgroundThe phlebostatic axis is the most commonly used anatomical external reference point for central venous pressure measurements. Deviation in the central venous pressure transducer alignment from the phlebostatic axis causes inadequate pressure readings, which may affect treatment decisions for critically ill patients in intensive care units. AimThe primary aim of the study was to assess the variability in central venous pressure transducer levelling in the intensive care unit. We also assessed whether patient characteristics impacted on central venous pressure transducer alignment deviation. MethodsA sample of 61 critical care nurses was recruited and asked to place a transducer at the appropriate level for central venous pressure measurement. The measurements were performed in the intensive care unit on critically ill patients in supine and Fowler's positions. The variability among the participants using eyeball levelling and a laser levelling device was calculated in both sessions and adjusted for patient characteristics. ResultsA significant variation was found among critical care nurses in the horizontal levelling of the pressure transducer placement when measuring central venous pressure in the intensive care unit. Using a laser levelling device did not reduce the deviation from the phlebostatic axis. Patient characteristics had little impact on the deviation in the measurements. ConclusionThe anatomical external landmark for the phlebostatic axis varied between critical care nurses, as the variation in the central venous pressure transducer placement was not reduced with a laser levelling device. Standardisation of a zero-level for vascular pressures should be considered to reduce the variability in vascular pressure readings in the intensive care unit to improve patient treatment decisions. Further studies are needed to evaluate critical care nurses' knowledge and use of central venous pressure monitoring and whether assistive tools and/or routines can improve the accuracy in vascular pressure measurements in intensive care units.

Thermal to optical energy conversion: A multi megawatt carbon dioxide laser driven by an extremely high temperature gas cooled reactor

In the conversion of ionizing radiation into energy, the production of heat is the most common first step in energy conversion systems, but it is also possible to use ions and excited states as the first step. The difference being that nearly all of the energy content of ionizing radiation is converted to heat but only 40–50% of the energy content of ionizing radiation is converted into ions and excited states. Conversion of the energy contained in ionizing radiation into ions and excited states starts out at a considerable disadvantage. Nuclear-pumped lasers have typically depended on the conversion of ionizing radiation into ions and excited states as a first step. Among the reasons that nuclear-pumped lasers have had low system efficiencies (1–2.5%) is the considerable inefficiencies in producing ions and excited states from ionizing radiation. A nuclear-pumped laser system which uses heat produced from the energy content of ionizing radiation as the driver for the laser system is described in this paper. The conversion of heat into vibrational states in molecular nitrogen allows energy to be stored in a long lived molecular state which can then be transported spatially where its energy is collisionally conveyed to carbon dioxide molecules in a resonance transfer process to produce the carbon dioxide upper laser level. The carbon dioxide laser emits a laser beam with a wavelength centered at 10.4 μm. The nitrogen vibrational state and its resonance conversion into the carbon dioxide upper laser level is one of nature's most efficient processes in laser physics (with laser efficiencies approaching ∼20% primarily being driven by the resonance process-extremely high for a laser). The laser system described here takes advantage of this highly efficient mechanism for conversion of thermal energy to optical energy. The feasibility of using nuclear rocket core technology for the generation of high temperature gas flows to power this thermal to optical conversion process is described. This study indicates that the thermal to optical conversion process can lead to a carbon dioxide laser with efficiencies on the order of 7% or perhaps better. Such a system would have potential applications in power beaming, space propulsion, asteroid mining, asteroid deflection and potential military applications.

A GaInAs/AlInAs quantum cascade laser with an emission wavelength of 5.6 μm

A quantum cascade laser based on a strain-compensated Ga0.4In0.6As/Al0.58In0.42As heteropair is developed, which operates in the pulse regime in the wavelength range of 5.5–5.6 μm at temperatures of up to at least 350 K. It became possible due to an increase in the quantum well depth and to the usage of the two-phonon depopulation mechanism for the lower lasing level. The calculated voltage defect is about 100 meV. The laser epitaxial hetero-structure was grown by the MOVPE method. It was investigated by the high-resolution X-ray diffraction technique. It is shown that the heterostructure has a high quality with bandwidths of main satellite peaks of 55 arcsec. The threshold current density is 1.6 kA cm–2 at 300 К. The characteristic temperature is T0 = 161 K for the temperature interval of 200 – 350 K. For the laser of size 20 μm × 3 mm with cleaved mirrors, the maximum pulsed power is 1.1 W at 80 K and 130 mW at 300 K.The bibliography includes 13 references.

Factors determining the adoption of laser land leveling in the irrigated rice–wheat system in Haryana, India

ABSTRACTLaser land leveling has been increasingly adopted in the irrigated rice (Oryza sativa L.)–wheat (Triticum aestivum L.) cropping system in the state of Haryana (India), located in the north-western Indo-Gangetic Plains. Still, many farmers have applied it to only a fraction of their land. In this study, we used data collected from 621 farm households in Haryana and applied a double-hurdle model for assessing the factors that determine the adoption and intensity of laser-leveling technology. The results show that large land holders are more likely to laser level their farm land; however, we found a negative association between land holdings and the proportion of laser-leveled land. Information about technology through farmer-to-farmer communication and through private traders, participation in agricultural training and membership in local agricultural institutions increased both the likelihood and the intensity of adoption. Our findings call for a closer collaboration among the various stakeholders, specifically to promote farmer-to-farmer communication through increased participation in local institutions and increase the rate of adoption of laser leveling technology.

Sensitization and deactivation effects to Er3+ at [formula omitted]2.7 μm mid-infrared emission by Nd3+ ions in Gd0.1Y0.9AlO3 crystal

The use of Nd3+ codoping for sensitizing the Er3+ ion and enhancing the ∼2.7 μm emission from transition of Er3+:I11/24→I13/24 were investigated in the Er/Nd codoped Gd0.1Y0.9AlO3 (GYAP) crystal for the first time, to the best of our knowledge. The ∼2.7 μm emission characteristics and the energy transfer mechanism of the as-grown crystals were investigated in details. On one hand, it is found that the codoped of Nd3+ ion can act as an appropriate sensitizer for Er3+ ion in GYAP crystal, making the Er/Nd:GYAP crystal can be pumped by commercialized 808 nm laser diodes (LD). On the other hand, the Nd3+ ions can also act as a suitable deactivated ion for Er3+ ions with efficient depopulation effect on the lower laser level Er3+:I13/24 for enhancing the ∼2.7 μm fluorescence emission, while having little influence on the upper laser level of Er3+:I11/24. With these favorable properties, the Er/Nd:GYAP crystal may become an attractive host for developing solid state lasers at around 2.7 μm under a conventional 808 nm LD pump.

The effect of external cavity reflectivity on the dynamic behaviors of quantum cascade laser

The effect of external reflectivity on the dynamic behaviors of quantum cascade laser coupled to external cavity is theoretically investigated. Our model is based on three-level rate equations including the dependence of the loss on external cavity parameters. We find in particular that the effective reflectivity, photon lifetime and threshold current are strongly influenced by the external cavity length and external reflectivity. The optimum external cavity length (Lext) is about 4 cm. We also show that the external cavity reflectivity influences significantly the dynamics of the electron number in the upper and lower laser levels, population inversion, and photon numbers in the Fabry Perot and in the external cavities. In addition, the external cavity reflectivity dependences of turn-on delay time (tth) is also studied and discussed.

Enhanced 14 μm emissions of Tm3+ via Tb3+ deactivation in (Gd05Lu05)2SiO5 crystal

The use of Tb3+ codoping for the enhancement of the transition of Tm3+:3H4→3F4 ∼1.4 μm emissions was investigated in the Tm3+/Tb3+ codoped (Gd0.5Lu0.5)2SiO5 (Tm/Tb:GLSO) crystal for the first time. The ∼1.4 μm fluorescence emission properties and energy transfer mechanism of the as-grown crystals were investigated in detail. It is found that the codoped of Tb3+ ion in Tm/Tb:GLSO crystal greatly enhances Tm3+:1.4 μm emission under excitation of a common 789 nm laser diode, depopulates the lower laser level of Tm3+:3F4, and has little effect on the upper laser level of Tm3+:3H4 at the same time. The energy transfer efficiency from the Tm3+:3F4 level to the Tb3+:7F0 level is as high as (74.4±1.5)%, indicating that the Tb3+ ion is an effective deactivation ion for enhancing the ∼1.4 μm emission in Tm/Tb:GLSO crystal. These results suggest that Tm/Tb:GLSO crystal may be a promising material for ∼1.4 μm laser under the pump of a conventional 789 nm LD.

Above room temperature operation of InGaAs/AlGaAs/GaAs quantum cascade lasers

In this work we report on the performance of mid-infrared quantum cascade lasers (QCLs) based on strained InGaAs/AlGaAs grown by molecular beam epitaxy on GaAs substrate. Structures were grown with indium content from 1% to 6% in GaAs quantum wells (QW) and 45% of Al in AlGaAs barrier layers. The design results in strained heterostructure, however, no strain relaxation was observed as documented by x-ray diffraction measurements up to ∼3% of In content in QWs. The investigation of heterostructures and devices was performed, including structural measurements and electrooptical characterization of devices. Devices fabricated from epi wafers with 2.64% of In exhibited performance largely improved over GaAs/AlGaAs QCLs. Roughly two times reduction of the threshold current density was observed at lasing wavelength ∼9.45 μm. The lasers operated in pulsed mode up to T = 50 °C with characteristic temperature T0 = 115 K. The decrease of the threshold current density has been mainly attributed to the reduction of interface roughness scattering and the increase of activation energy for the escape of carriers from the upper laser level to the 3D continuum. Further increase of In content in QWs resulted in the deterioration of device parameters.

Laser generation on Yb:LuAG ceramics produced by nanocrystalline pressure-less sintering in H2

The spectral and laser properties of 3 at.% Yb3+:Lu3Al5O12 ceramics produced by a new method of nanocrystalline pressure-less sintering in H2 were investigated. The studied sample had a transmittance close to the theoretical value (83.3% at λ = 1070 nm) and a laser level lifetime of 0.93 ms. Laser generation in different regimes with a maximum slope efficiency of 54% and a maximum average power of 206 W was attained, which makes this method highly promising for producing ceramics for lasers with multi-kilowatt average power.

An overview of use of precision farming technologies by the farmers- A case study of North Eastern Karnataka

Agriculture in future can be expected to be competitive, knowledge-intensive and market driven. Modern frontier technologies involving systems approach towards efficient crop and input management, land and water use planning are essential for Indian agriculture to meet the challenges in the present context. Further, increasing the productivity level of a pollution free technological factor of production is inevitable. With this concern the present study was carried out in North Eastern parts of Karnataka state, where the precision farming technology was implemented. Hence, an attempt has been made through present paper to study the extent of usage of precision farming technologies at farm level. The technologies implemented were GPS, GIS, variable rate applications of inputs, crop sensors etc. Adopters were aware of benefits of management aspects like size of grid, soil sampling, soil analysis, variable rate of application of fertilizers, laser levelling and harvesting by grids. But still, precision farming has yet to take its firm ground in India by moving from its infant stage. This is possible by dissemination of technology and its benefits by bringing awareness among farming community through efforts of Department of Agriculture by using SAUs and NGOs as channels.

Rate equation modeling of the frequency noise and the intrinsic spectral linewidth in quantum cascade lasers.

This work theoretically investigates the frequency noise (FN) characteristics of quantum cascade lasers (QCLs) through a three-level rate equation model, which takes into account both the carrier noise and the spontaneous emission noise through the Langevin approach. It is found that the power spectral density of the FN exhibits a broad peak due to the carrier noise induced carrier variation in the upper laser level, which is enhanced by the stimulated emission process. The peak amplitude is strongly dependent on the gain stage number and the linewidth broadening factor. In addition, an analytical formula of the intrinsic spectral linewidth of QCLs is derived based on the FN analysis. It is demonstrated that the laser linewidth can be narrowed by reducing the gain coefficient and/or accelerating the carrier scattering rates of the upper and the lower laser levels.

Assessing land leveling needs and performance with unmanned aerial system

Land leveling is the initial step for increasing irrigation efficiencies in surface irrigation systems. The objective of this paper was to evaluate potential utilization of an unmanned aerial system (UAS) equipped with a digital camera to map ground elevations of a grower’s field and compare them with field measurements. A secondary objective was to use UAS data to obtain a digital terrain model before and after land leveling. UAS data were used to generate orthomosaic images and three-dimensional (3-D) point cloud data by applying the structure for motion algorithm to the images. Ground control points (GCPs) were established around the study area, and they were surveyed using a survey grade dual-frequency GPS unit for accurate georeferencing of the geospatial data products. A digital surface model (DSM) was then generated from the 3-D point cloud data before and after laser leveling to determine the topography before and after the leveling. The UAS-derived DSM was compared with terrain elevation measurements acquired from land surveying equipment for validation. Although 0.3% error or root mean square error of 0.11 m was observed between UAS derived and ground measured ground elevation data, the results indicated that UAS could be an efficient method for determining terrain elevation with an acceptable accuracy when there are no plants on the ground, and it can be used to assess the performance of a land leveling project.

The efficacy of fractional CO2 laser resurfacing in the treatment of facial acne scars

Background: Acne is a common condition with prevalence as high as 80% among adolescents and often it causes atrophic scars. Laser resurfacing is an effective treatment for acne scars. However, post-treatment adverse effects are often induced. Fractional laser photothermolysis has been designed to create microscopic thermal wounds to achieve skin rejuvenation without significant side effects. Objectives: The aim of this study is to assess the efficacy and safety level of fractional CO2 laser in atrophic acne scars treatment. Materials and Methods: Forty patients between 18 and 40 years of both sexes with atrophic acne scars seen in the Department of Dermatology at Najran University Hospital in Najran, Saudi Arabia, were treated with 4–6 sessions of fractional CO2 laser resurfacing. The result was evaluated objectively at each follow-up visit and 3 months after the last laser session using a quartile grading scale. Patient improvements were classified as excellent when the improvement was >50% in scar outcome and appearance of skin, good if 25–50% response, and poor when the response

Температурная зависимость порогового тока и выходной мощности квантово-каскадного лазера с частотой генерации 3.3 ТГц

AbstractThe active region of a THz (terahertz) quantum-cascade laser based on three tunnel-coupled GaAs/Al_0.15Ga_0.85As quantum wells with a resonance-phonon depopulation scheme is designed. Energy levels, matrix elements of dipole transitions, and gain spectra are calculated as functions of the applied electric-field strength F and temperature. It is shown that the maximum gain is implemented at a frequency of 3.37 THz and F = 12.3 kV/cm. Based on the proposed design, a quantum-cascade laser emitting at ~3.3 THz with a double metal waveguide and T _max ~ 84 K is fabricated. The activation energy E _ a = 23 meV for longitudinal-optical (LO) phonon emission upon the stimulated recombination of hot electrons from the upper laser level to the lower one is determined from the Arrhenius temperature dependence of the output power.

Highly efficient CW laser operation in 4 at. % Tm3+ and 4 at. % Y3+ codoped CaF2 crystals

Tm:CaF2 and Tm,Y:CaF2 single crystals were prepared by the temperature gradient technique. The spectral properties of Tm,Y:CaF2 single crystals were investigated and compared with those of Tm:CaF2. It was demonstrated that codoping with Y3+ ions could efficiently improve the spectroscopic properties. Tm,Y:CaF2 crystals have larger absorption cross-sections at the pumping wavelength, larger mid-infrared stimulated emission cross-sections, and much longer fluorescence lifetimes of the upper laser level (Tm3+: H43 level) than Tm:CaF2 crystals. Continuous-wave (CW) lasers around 1.97 μm were demonstrated in 4.0 at. % Tm,4.0 at. % Y:CaF2 single crystals under 792 nm laser diode (LD) pumping. The best laser performance has been demonstrated with a low threshold of 0.368 W, a high slope efficiency of 54.8%, and a maximum output power of 1.013 W.