Lasing in the far IR spectral range under femtosecond optical excitation of the InAs semiconductor in a magnetic field

The generation of high pulse and average power radiation in eye-safe spectral region by the third stokes generation in barium nitrate Raman laser

Defect transformations in nitrogen-doped CVD diamond during irradiation and annealing

power of optical radiation in fiber-optic transmission systems has now been completed at the All-Russia Research Institute of Optophysical Measurements (VNIIOFI) [1‐5]. The operation of these systems is based on the method of substitution of the average power of optical radiation affecting a standard transducer the unit of which is reproduced by the average power of a constant electric current. The process consists of preliminary electrical calibration of the transducer, subsequent transmission of radiation to the transducer, and the determination of the average power with the use of the value of the conversion factor of the electric current obtained in the course of calibration as well as the coefficient of equivalence of substitution determined in the course of certification of a standard calorimetric system. This, in general outline, is how the algorithm used for reproduction of the unit of average power of optical radiation in the new reference systems may be represented. In the course of developing high-precision reference systems, it has become necessary to find and select the most efficient circuits and designs of instruments incorporated into the circuits by means of which the required reproduction precision may be attained. As a result, high-precision standard calorimetric transducers of the average power of optical radiation in fiber-optic transmission systems and calibration systems that include highly stable sources of constant electric current have been created. The most precise multimeters for measurements of this current and voltage in the course of calibration, nanovoltmeters for measurements of the output signals of the transducers, meteoscopes (weather forecast software) for monitoring the parameters of the environment and introducing particular corrections into the results of measurements have also been selected. In addition, considerable emphasis has been devoted to the search for and selection of optimal designs of the optical circuits of the newly created reference systems. Besides stabilized sources of radiation, these systems also include fiber-optical cables that transmit radiation, light shutters, radiation flux dividers in standard and control channels, instruments for measurement of the average radiation power in control channels, and a number of other elements.

The cumulative retardance Delta(t) introduced between the p and the s orthogonal linear polarizations after two successive total internal reflections (TIRs) inside a right-angle prism at complementary angles phi and 90 degrees - phi is calculated as a function of phi and prism refractive index n. Quarter-wave retardation (QWR) is obtained on retroreflection with minimum angular sensitivity when n=(sqr rt 2+1)(1/2)=1.55377 and phi =45 degrees. A QWR prism made of N-BAK4 Schott glass (n=1.55377 at lambda=1303.5 nm) has good spectral response (<5 degrees retardance error) over the 0.5-2 microm visible and near-IR spectral range. A ZnS-coated right-angle Si prism achieves QWR with an error of < +/- 2.5 degrees in the 9-11 microm (CO(2) laser) IR spectral range. This device functions as a linear-to-circular polarization transformer and can be tuned to exact QWR at any desired wavelength (within a given range) by tilting the prism by a small angle around phi =45 degrees. A PbTe right-angle prism introduces near-half-wave retardation (near-HWR) with a < or =2% error over a broad (4< or =lambda< or =12.5 microm) IR spectral range. This device also has a wide field of view and its interesting polarization properties are discussed. A compact (aspect ratio of 2), in-line, HWR is described that uses a chevron dual Fresnel rhomb with four TIRs at the same angle phi =45 degrees. Finally, a useful algorithm is presented that transforms a three-term Sellmeier dispersion relation of a transparent optical material to an equivalent cubic equation that can be solved for the wavelengths at which the refractive index assumes any desired value.

The effect of treatments in plasmas of different gases and subsequent deposition of diamond-like carbon films (DCFs) on the transmission of semi-insulating GaAs crystals in the IR spectral range has been analyzed. It is shown that deposition of 1- to 1.5-μm DCFs makes it possible to increase the GaAs transmission in the range of 4–15 μm and that preliminary treatment in H+ or Ar+ plasma increases the optical transmission of the DCF-GaAs structure. A mechanism is proposed to explain the effect of plasma treatment on the optical transmission of semi-insulating GaAs in the IR spectral range.

Summary form only given. Solid-state lasers at 2.1 μm having many applications for medical surgery, atmospheric wind lidar, gas detection, material processing and pumping of mid-IR optical parametric oscillators are attracting great interest in the last years. Tm- and Ho-doped sesquioxides (Tm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup> :Lu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> , Tm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup> :Sc <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> , Ho: <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup> :Lu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> and others) having an extraordinary long-wavelength 2-μm luminescence band and a high thermal conductivity open up new opportunities for highly efficient laser generation at around 2.1 μm [1]. Transparent laser ceramic materials are attracting great interest as a substitute for the single crystals. Recently, the high-quality sesquioxides ceramics doped by Nd <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup> or Yb <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup> ions have demonstrated good potential for the efficient laser oscillation. This presentation is an overview of our investigations of the 2.1- μm lasers based on the novel Tm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup> :Lu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> ceramics with diode or laser pumping at 796 or 810 nm [2-6].Structural, optical and spectroscopic properties of novel Tm3+:Lu2O3 ceramics, produced by "Konoshima Chemicals Co." (Japan), were studied [2-4]. The average grain size is determined to be ~ 0.55 μm. The absorption spectra show good opportunities for diode or laser pumping at 796 nm and 811 nm. The ceramics have high mid-IR transmittance of up to 7 μm. Strong luminescence lines centered at 1942 nm, 1965 nm and 2066 nm were detected. The thermal conductivity and the thermal index gradient of the ceramics were determined (by kinetic-resolvable interferometric and grating testing methods) to be comparable with the single crystal [4]. 2.1-μm laser-oscillators based on Tm3+:Lu2O3 ceramics pumped by 796-nm or 810-nm laser diodes were created and studied [2,3]. CW operation with average power of ~ 35W and optical-to-optical efficiency of ~ 34% and the slope efficiency (with respect to absorbed power) of ~ 44% was demonstrated. The oscillations wavelength was tuned in spectrum region of 2060 - 2098 nm. 1-10 kHz periodically-pulsed generation was realized by active Q-switching (by a quartz acousto-optic modulator). The average power of the Q-switched radiation reached 7 W, corresponding peak power was up to 10 kW. Cr2+:ZnSe saturable absorber was also investigated as an passive Q-switcher of the ceramics lasers. An ion-implanted InGaAsSb quantum-well-based SESAM was applied for realization of the passive modelocking oscillations in the Tm3+:Lu2O3-ceramic lasers [5]. Transform-limited pulses as short as 180 fs were generated at 2076 nm with an average output power of 400 mW and a pulse repetition frequency of 121.2 MHz. An output power up to 750 mW was reached at the longer pulse duration of 382 fs. Femtosecond pulse generation tuned in 2030-2100 nm spectral range was realized. A single-layer graphene was used also for mode-locking in the ceramics Tm:Lu2O3 laser [6]. The transformlimited 410 fs pulses with a spectral width 11.1 nm at 2067 nm were registered. The maximum average output power was 270 mW, at a pulse repetition frequency of 110 MHz. This is a convenient high-power transform-limited ultrafast laser at 2 μm for various applications, such as laser surgery and material processing.

It is demonstrated experimentally that at high average radiation power, the optical isolation in the recently proposed design of a Faraday isolator is substantially higher than in the conventional scheme. The Faraday isolator with the isolation of 45 dB at the radiation power of 100 W is implemented. The data obtained show that a 30-dB isolator for the average laser radiation power of 1 kW can be realised.

Carbon-rich amorphous silicon carbide and silicon carbonitride films for silicon-based photoelectric devices and optical elements: Application from UV to mid-IR spectral range

We demonstrate a power-scalable concept for high-power all-solid-state femtosecond lasers, based on passive mode locking of Yb:YAG thin disk lasers with semiconductor saturable-absorber mirrors. We obtained 16.2 W of average output power in pulses with 730-fs duration, 0.47-muJ pulse energy, and 560-kW peak power. This is to our knowledge the highest average power reported for a laser oscillator in the subpicosecond regime. Single-pass frequency doubling through a 5-mm-long lithium triborate crystal (LBO) yields 8-W average output power of 515-nm radiation.

The main features of obtaining refractory oxide nanopowders using a repetitively-pulsed CO2-laser (10,6 µm) with an average radiation power of 500 W or a CW ytterbium fiber laser (1,07 µm) with a radiation power of up to 700 W are considered. In particular, the influence of pressure, buffer gas composition and average radiation power on the size of nanoparticles and the productivity of their obtaining were studied. Depending on the thermophysical properties of the material, in atmospheric pressure air the productivity of nanopowder synthesis varies from 15 – 23 g/h (YSZ) to 350 g/h (WO3). The mass yield of nanopowder obtained upon evaporation of one target is usually is 30 wt. % of the weight of the initial target. The obtained nanopowders contain weakly agglomerated nanoparticles of spherical shape. The average size of nanoparticles 11 – 20 nm weakly depends on their material. The most important features of using a CW ytterbium laser to obtain nanopowders of refractory oxides are their high transparency for radiation of 1,07 μm, as well as the spraying of many melt droplets. These features led to a reduction in the productivity of nanopowder production and its mass yield. On the other hand, the scattering of laser radiation in porous of the initial target and its concentration in some regions makes it possible to efficiently evaporate oxide targets from materials with a refractive index of more than 1.7 – 1.75. The transition to a repetitively-pulsed mode of radiation (pulse duration 120 μs, square waveform, and peak power 600 W), an increase in the spot diameter and the speed of beam movement over the target surface made it possible to significantly reduce droplet spattering and increase the yield of Nd: Y2O3 nanopowder from 9,7 to 30 wt.% of the weight of the initial target. However, a twofold decrease in the average radiation power led to the fact that the productivity of obtaining the nanopowder was only 15 g/h. Thus, to obtain nanopowders of refractory oxides, it is desirable to use a quasi-CW fiber ytterbium laser, which is specially designed for operation in a repetitively pulsed mode. The obtained nanopowders YSZ, Nd: Y2O3, Al2O3, etc. are used for the manufacture of ceramic solid electrolytes of the YSZ type and highly transparent laser ceramics.

The Planetary Spectroscopy Laboratory (PSL) of DLR in Berlin provides spectral measurements of primarily planetary analogues from the visible to the far-infrared range. PSL has supported the data analysis as well as the development and calibration of instruments for planetary missions from ESA, NASA and JAXA. For this purposes PSL provides reflection, transmission and emission spectroscopy of target materials. Currently PSL operates three identical Bruker Vertex 80V vacuum FTIR spectrometer (the third one just installed in June 2019), two spectrometers are equipped with aluminum mirrors optimized for the UV, visible and near-IR, the third features gold-coated mirrors for the near to far IR spectral range. External simulation chambers are attached to two of the instruments for emissivity measurements. The chamber at the near to far IR instrument allows emissivity measurements from 0.7-200 μm under vacuum for sample temperatures from 320K to above 900K, using an innovative induction system. The second chamber (purged with dry air and water cooled to ≤270K) allows emissivity measurements of samples with surface temperature from 290K to 420K. We measure bi-directional reflectance of samples; with variable incidence and emission angles between 0° and 85° (minimum phase angle is 26° to prevent damages to the mirrors). Samples are measured currently at room temperature and 170K, with a planned extension for temperatures below 100K, by means of a new external chamber, whose funding is accepted and will be available in 2020. Bi-directional and hemispherical reflectance is measured under purging/vacuum conditions, covering the 0.2 to above 200 μm spectral range. An FT-IR microscope installed at the end of 2018, allows microscopic analysis in transmission and reflectance in the VIS+VNIR+MIR spectral range. Transmission of thin slabs, optical filters, optical windows, pellets, and others is measured in the complete spectral range from UV to FIR using a parallel beam configuration to avoid refraction

Spectroscopy is still the most accurate methodology to remotely study the surface composition of celestial bodies (and its evolution). For more than ten years the Planetary Emissivity Laboratory (PEL) of DLR in Berlin has provided spectral measurements of planetary analogues from the visible to the far-infrared range for comparison with remote sensing spacecraft/telescopic measurements of extra-terrestrial surfaces [1-5]. Reflection, transmission and emission spectroscopy are the techniques we used to acquire spectral data of target materials.&#13;\nA recent major upgrade to our laboratory set-up added a new spectrometer, three external sources, optical units, new detectors and beamsplitters to further extend the spectral range of measurements that can be performed in the laboratory, as well as the temperature range that we can cover for the measurements. The purpose of this paper is to illustrate the very wide range of capabilities that the Planetary Spectroscopy Laboratory (PSL) can offer to the planetary and to the spectroscopic community.

It is well known that the optical materials are unique and perspective. Optical materials and the devices based on them are operated in the broad spectral range: In the UV spectral range (where the wavelength l is approximately placed in the range of ~ 0.1 - 0.4 microns), in the VIS spectral range (l ~ 0.5 - 0.75 microns), and in the IR spectral range (l is larger than the 0.75-1 microns). These materials can be considered to resolve the different complicated tasks. To study optical materials different techniques and methods should be scrupulously used. Among different applied methods namely the laser oriented technique and nanostructuration approach have some unique features. It can be considered as the effective dominant approach in order to reveal the change of all basic physical-chemical characteristics of the materials. Our own steps in this direction have partially been recently shown too. In the current paper, advantages of the modification of optical material surfaces via a nanotechnology approach will be shown. The surface relief change provokes the spectral, mechanical and wetting phenomena changes. A CO2-laser is applied to modify the optical materials surfaces under the condition when the carbon nanotubes are deposited in vertical position at the materials surfaces. This process permits to organize covalent bonding between the carbon atoms and the model matrix ones. An emphasis will be given on the surface modifications of the materials, such as: LiF, CaF2, KBr, BaF2, Sc, some polymer surface, etc. Mechanisms responsible for the spectral characteristics change, mechanical hardness as well as the increase of the wetting angle will be discussed. The area of the application of the materials studied can be increased.

The article considers the development of metrological assurance in the field of measurements of the average power of optical radiation in the spectral range 0.6–1.7 μm for fiber-optic communication and information transmission systems, the creation of State Primary Special Standard GET 170–2011 of the unit of length and unit of propagation time of a signal in a waveguide, and the average power, attenuation, and wavelength for fiber-optic communication and information transmission systems.

The lifetime of the first electronically excited state of sodium-ammonia (Na(NH3)n) clusters is investigated with femtosecond laser pulses in the visible and near IR spectral range. The decay time of the pump-probe ion signal decreases drastically with increasing cluster size from 1000 ps (n=l) to 0.1 ps for n = 15. Different decay mechanism are discussed. A purely statistical process can be excluded to be responsible for the observed decay times.KeywordsExcited StateFemtosecond Laser PulseProbe PulseSolvation ShellSodium AtomThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.