Spectral Half-width Research Articles

Single frequency pulsed Er,Yb co-doped fiber amplifier with 2 mJ of output energy

High-energy single-frequency pulsed light with low noise is generated from a master oscillator power amplifier (MOPA) system at 1.55 μm eye-safe wavelength using an ultra large mode area Er-Yb gain fiber. At a pulse repetition rate of 2 kHz, the maximum pulse energy without stimulated Brillouin scattering (SBS) reaches 2.07 mJ with 375 ns pulse duration for a pump power of 56.4 W. The pulse energy fluctuation is approximately 0.72 % within 21.5 min. The signal noise ratio (SNR) from the single-frequency fiber amplifier, at the highest pulse energy, centered at 1551.1 nm, is approximately 30 dB. The spectral half width of the signal light is calculated to be 1.28 MHz, which is close to the transform limit.

Unusually Powerful Flare Phenomenon of the Water Maser in W51 and the Possibility of Detecting Gravitational Radiation from It

Because of detailed monitoring of the 22.2 GHz water maser, carried out from 2021 October to 2023 May, a very powerful flare phenomenon was detected in the galactic object W51 near the radial velocity of 60 km s−1 with the amplitude of 140 kJy. A phenomenon of this magnitude was unprecedented in the entire history of observations of the source. Eleven short flares were recorded. The exponential increase and decrease in the flare flux density while reducing in their spectral line widths indicated that water masers were in an unsaturated state during the flares. All flares were located at the top of the less powerful Flare 0 with the amplitude of 13.5 kJy and the spectral line half-width of 3.0 km s−1. Such a wide line of the water maser, as well as the amplitude, of the flare phenomenon are so far unique discoveries. The water maser of Flare 0 may have been saturated and created a significant input flux density for other flares of this phenomenon. The extremely high density of maser spots in a cluster led to their partial overlap on the observer’s line of sight. This also confirmed the hypothesis about the need for a significant length of the path along which the generation of maser radiation occurs. New parameters of water masers and the most important physical conclusions have been obtained. The possibility of detecting gravitational waves from massive binary stars at the stage of evolution close to merging is considered for the case of W51 Main.

Spontaneous and stimulated Raman scattering by the products of the interaction of lithium deuteride with the environment

The processes of spontaneous and multicomponent stimulated Raman scattering (SRS) in a polycrystal consisting of the products of the interaction of lithium deuteride crystals with air molecules are studied. The interaction of lithium deuteride with environmental molecules resulted in a solid polycrystalline mixture of LiOH, LiOD, LiOH·H2O, and Li2CO3 on the crystal surface. Excitation of the sample under study by the third harmonic of a picosecond repetitively pulsed YAG:Nd3+ laser made it possible to detect three Stokes and the second anti-Stokes SRS components with a Raman frequency ν = 3660 cm−1 corresponding to the valence breathing mode of the OH− ion. A feature of the obtained spectra is the smaller spectral half-width of the second and third Stokes components compared to the first. When the studied polycrystals were excited by picosecond radiation with a wavelength λ = 532 nm, two Stokes and one anti-Stokes SRS components corresponding to the internal symmetric vibrational mode of LiOH were detected. The excitation of SRS at the Raman frequency of the OH− vibration ν = 3660 cm−1 in solids is promising due to the high-frequency shift and high quality factor, and is also important for studying the strength of hydrogen bonds.

Saturation Spectroscopic Studies on Yb3+ and Er3+ Ions in Li6Y(BO3)3 Single Crystals

The results of a series of pump–probe spectral hole-burning experiments are presented on Yb3+- or Er3+-doped Li6Y(BO3)3 (LYB) single crystals in the temperature range of 2–14 K and 9–28 K, respectively. The spectral hole has a complex structure for Yb3+ with superposed narrow and broad bands, while a single absorption hole has been observed for Er3+. Population relaxation times (T1) at about 850 ± 60 μs and 1010 ± 50 μs and dipole relaxation times (T2) with values of 1100 ± 120 ns and 14.2 ± 0.3 ns have been obtained for the two components measured for the Yb3+:2F7/2—2F5/2 transition. T1 = 402 ± 8 μs and T2 = 11.9 ± 0.2 ns values have been found for the Er3+:4I15/2—4I11/2 excitation. The spectral diffusion rate at about 1 and 5 MHz/ms has been determined for the narrow and broad spectral line in Yb3+-doped crystal, respectively. The temperature dependence of the spectral hole halfwidth has also been investigated.

Focus on lasers, imaging, and microscopy

Focus on lasers, imaging, and microscopy

Characterization of zirconium oxides part I: Raman mapping and spectral feature analysis

Abstract Raman mapping of sectioned zirconium cladding oxides was performed to analyze different spectral features before and after breakaway, as well as between zirconium and its alloys Zr-2.65Nb, Zry-3, and Zry-4. Oxide phase composition, or percent tetragonality, was defined to compare tetragonal to monoclinic zirconia. Percent tetragonality was spatially mapped to support distinction of zirconia phase distribution. A tetragonal-rich layer was seen at the metal/oxide interface, while post-breakaway samples exhibited increased amount of tetragonal phase in the bulk of their oxides. Spatial mapping of spectral peak location and half-width at half-maximum was accomplished to distinguish differences in stability mechanisms of tetragonal-rich zirconia phase. Shifts in monoclinic peak positions provided mapping of relative stress state, supporting the differences in stabilization of tetragonal phase near the metal/oxide interface and tetragonal phase in the bulk of the oxide. Tetragonal phase near the metal/oxide interface is stabilized through support of oxygen sub-stoichiometry and compressive stress. Tetragonal phase observed in the bulk of the oxide is stabilized through oxygen sub-stoichiometry, void of compressive stress. A linear trend between percent tetragonality and stress state was determined. This resulted in a connection between mechanism of tetragonal to monoclinic phase transformation and a cladding's ability to resist oxidation and breakaway. Poor performing samples displayed greater stress gradients, driven by lattice mismatch at the metal/oxide interface, as well as between tetragonal and monoclinic phase boundaries. Tetragonal phase at the metal/oxide interface for superior performing samples have reduced epitaxial growth of tetragonal grains, lowering compressive stress gradients and provided more resistant inner-oxide layers. With increased utility of Raman spectroscopy for characterizing zirconium cladding materials, different degradation mechanisms can be further understood.

Reflection Spectra of Composite Photonic Crystals Based on Anodic Alumina Filled with Ferroelectric Sodium Nitrite

Reflection spectra of a composite one-dimensional photonic crystal (PC) based on porous anodic alumina filled with ferroelectric sodium nitrite have been recorded in the wavelength range of 400 to 1200 nm. Significant spectral shifts of the first and second stopbands are revealed for the composite PC. The stopband spectral half-width is found to decrease by a factor of four to five. The possibility of applying composite alumina-based photonic crystals as selective narrowband mirrors is discussed.

Superluminescent diodes of the 770 – 790-nm range based on semiconductor nanostructures with narrow quantum wells

Comparative experimental study of superluminescent diodes (SLDs) with active layers containing one, two, or three 5.0-nm-wide quantum wells symmetrically positioned in the waveguide layer is performed. It is shown that an increase in the number of quantum wells leads to narrowing of the superluminescence spectrum and weakens the dependence of its width on the pump level. Simultaneously, the degree of polarisation of the output radiation noticeably increases. For example, rather reliable high-power narrow-band SLDs with a spectral halfwidth smaller than 8 nm and polarisation ratio TE/TM exceeding 20 dB are developed.

Slow and fast light propagation through ladder-type atomic media with degenerate energy levels

We investigate the weak probe pulse propagation through the atomic medium, in the presence of the strong control laser field, under the regime of the electromagnetically induced transparency (EIT). These fields couple to the medium by forming the 3-level ladder configuration. We focus on two distinct cases: closed system, which is a non-degenerate, and open system, where the middle level is 3-fold degenerate, and the additional levels are coupled to the other levels only via spontaneous emission. The spatio-temporal profile of the probe pulse envelope is obtained by using the formalism of Maxwell-Bloch equations with the help of the Fourier transform method. We study the influence of the control field Rabi frequency, the spectral half-width of the initial pulse and decay rates on the propagation of the probe pulse. Several important pulse parameters are also calculated and discussed. It is shown that the group velocity of light can be controlled in such a manner that one can switch from slow to fast light and vice versa when changing the control Rabi frequency and spectral pulse half-width. Moreover, the possibility of replacing the open with an effective closed system is also discussed.

Absorption spectrum of thin films of KPb2(Cl1-xBrx)5 solid solutions

The absorption spectra of thin films of KPb2(Cl1-xBrx)5 (0 ≤ x ≤ 1) are studied in the spectral range of 2–6 eV (T = 90 K). Solid solutions with a mixed monoclinic structure are formed at all concentrations 0 ≤ x ≤ 1 and a tetragonal structure is found for 0.9 ≤ x ≤ 1. The temperature of the tetragonal to monoclinic phase transition in the solid solutions increases with the amount of Cl additive. The concentration dependences of the spectral location and half width of the long-wavelength exciton bands are the result of small-scale and large-scale fluctuations in the composition of the solid solution.

The exciton absorption spectrum of thin CuPb3Br7superionic conductor films

A study of the absorption spectrum of thin CuPb2Br7 films in the 2–6 eV spectral and 90–500 K temperature ranges. It is shown that the exciton spectrum of the compound is associated with transitions in the lead ion. The temperature dependence of the spectral position and half-width of the low-frequency exciton band contains features associated with phase transitions γ → β (Tc1 = 159 K) and β → α (Tc2 = 434 K) and the disordering of the cation sublattice of the compound in the transition to the superionic state.

Enhancement in laser performance of Er3+/Yb3+ Co-doped phosphate glass materials

Er3+/Yb3+co-doped phosphate are presented, laser glass materials with composition of P2O5-A12O3-BaCO3-KNO3-Li2O-ZnO-Er2O3-Yb2O3 (R-PABKLZ) are presented, in which an optimal molar ratio of 1:4 between Er3+ and Yb3+ was observed for achieving peak laser gain. Furthermore, due to adding 4.7 mol% Li1+ and 4.6 mol% Zn2+ ions into the glass, an optimum composition structure based laser material was demonstrated. On the other hand, since the high temperature melting method with changeable temperature control was used, the emission cross section of fluorescence, excited lifetime, and an effective spectral half width reached 9.70 × 10−21 cm2, 8.20 ms, and 53.16 nm, respectively, so that a laser gain (σemi×τrad) of 103.05 was obtained, which is significantly higher than previously reported results. The manuscript also argued the mechanism of relevant laser gain improvement.

Method of simultaneous measurement of two direction force and temperature using FBG sensor head.

This paper presents a method for measuring two components of bending force and temperature using one sensor head. Indirect inference based on the spectra of two fiber Bragg gratings (FBGs) placed on a cantilever beam is used. The method was developed during work on the inverse problem of determining a nonuniform stress distribution based on FBG spectra. A gradient in the FBG stress profile results in a characteristic shape of its reflective spectrum. The simultaneous measurements of force and temperature were possible through the use of an appropriate layout of the sensor head. The spectral characteristics of the sensor's gratings do not retain full symmetry, which is due to the geometry of the sensor's head and the related difference in the distribution of the axial stress of the gratings. In the proposed approach, the change in width of the sum of the normalized transmission spectra was used to determine the value of the applied force. In the presented method, an increase in the sensitivity of this change to the force is obtained relative to the other known systems. A change in the spectral width was observed for an increase in bending forces from 0 to 150 N. The sensitivity coefficient of the spectral width to force, defined as the ratio of the change of the spectral half-width to the change in force was 2.6e-3 nm/N for the first grating and 1.2e-3 nm/N for the second grating. However, the sensitivity of the whole sensor system was 5.8e-3 nm/N, which is greater than the sum of the sensitivities of the individual gratings. For the purpose of this work, a station with a thermal chamber has been designed with a bracket on which fiber optic transducers have been mounted for use in further measurements. The sensor head in this experiment is considered to be a universal device with potential applications in other types of optical sensors, and it can be treated as a module for development through its multiplication on a single optical fiber.

Research on the relationship between ideality factor and number of units of GaN-based high voltage light-emitting diode

Ideality factor can reflect the current, the carrier leakage, and the phenomenon of non-radiative recombination in light-emitting diode (LED). For the problem of ideality factor from current report about GaN-based LED, the value of ideality factor n is calculated by using the I-V curve fitting of high voltage LED. And the relationship between the ideality factor and the number of units is series in 12, 19, 51 and 80 V GaN-based high-voltage LED are discussed. In addition, the relationship between ideality factor and spectral half width (FWHM) is analyzed, and the impact of current crowding effect on the ideality factor is also studied. Results show that the ideality factor n increases nearly linearly with the number of units in series, indicating that the ideality factor n of high voltage LED is composed of its series units. It is a valuable result for understanding the ideality factor of GaN-based high voltage LED.

Fourier spectroscopy of water vapor in the volume of aerogel nanopores. Part 1. Measurements and calculations

Broadening and shifting of absorption lines of water vapor confined inside aerogel nanopores have been studied with the help of a IFS 125 HR Fourier spectrometer in the region 5000–5600 cm−1. It is shown that strong spatial limitation of molecular movement results in significant broadening and shifting of spectral lines. A semiempirical model for description of the form of absorption line contours for H2O molecules confined inside aerogel nanopores, taking account of the dependence of spectral line half-width on rotational quantum numbers, is presented for the first time. Values of spectral line half-widths found experimentally and theoretically are in good agreement.

Theory of relaxation parameters of the spectrum shape in the impact approximation−II: Simplifications, application for qQ(J,K) doublets in the v1 band of NH3 self-broadening

In the first part of this paper the general theory of relaxation parameters of the spectrum shape in the impact approximation was presented. Here we describe some simplifications, discuss the isolated line approximation and compare our results with the other methods of a spectral line half-width and center shift calculation. As an example, illustrative calculations of the qQ(J,K) doublets in the v1 band of NH3 self-broadening have been performed and the results are compared with the experiment.

Mycobacterium tuberculosis DNA Detection Using Surface Plasmon Resonance Modulated by Telecommunication Wavelength

A surface plasmon resonance sensor for Mycobacterium tuberculosis (MTB) deoxyribonucleic acid (DNA) is developed using repeatable telecommunication wavelength modulation based on optical fiber communications laser wavelength and stability. MTB DNA concentrations of 1 μg/mL and 10 μg/mL were successfully demonstrated to have the same spectral half-width in the dip for optimum coupling. The sensitivity was shown to be −0.087 dB/(μg/mL) at all applied telecommunication wavelengths and the highest sensitivity achieved was 115 ng/mL without thiolated DNA immobilization onto a gold plate, which is better than the sensor limit of 400 ng/mL possible with commercial biosensor equipment.

Monochromatization of semiconductor laser diodes using one-dimensional photonic crystals

The results on the development of the single-frequency semiconductor laser with external cavity based on a fiber Bragg grating (one-dimensional photonic crystal) formed in a single-mode fiber waveguide are presented. Stable single-frequency lasing at a wavelength of 977 nm with a spectral half width of 0.2 nm is achieved with a laser power output of 350 mW. The temperature dependence of lasing parameters is studied.

Near IR TDLS study of HF first overtone line shape. I. Experimental results

The HF first overtone vibration-rotational absorption spectral line profile (the transition 0–2 R(0)) broadened by Ar (mixture HF: Ar = 1: 150, T = 295 K, P = 10−300 mm Hg) is studied by the method of near IR diode laser spectroscopy. A tunable distributed feedback fiber diode laser was used as a radiation source in a two-channel spectrometer (λ ∼ 1.284 μm, spectral tuning range Δν = 1.5−2.0 cm−1, the output radiation power is 15 mW, the spectral half-width of lasing lines is ∼ 5 MHz). The broadening and shifting coefficients of the considered HF line are determined, using traditional Voigt, Rautian, and Galatry spectral profiles.

Characterization of InGaAsSbN layers grown on InP by MBE

AbstractOptical and electrical properties of the InGaAsSbN layers grown by molecular beam epitaxy (MBE) on InP substrates were studied in comparison with InGaAsN layers. It was found that the optical properties of the InGaAsSbN layer characterized by photoreflectance (PR) and photoluminescence (PL) measurements are superior to those of InGaAsN layer. In addition, electrical properties characterized by Hall measurements were also improved by adding Sb atoms. Annealing studies on photoluminescence properties of the InGaAsSbN layer revealed that the PL intensity increases and the PL spectral half width decreases upon annealing up to 700 °C. These results indicate that post‐annealing is still necessary for InGaAsSbN layers to improve crystalline quality (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)