Sidebands In Spectrum Research Articles

Eu3+ ions doped SrO-CaO-Li2O-B2O3glasses foroptical display material application

The glass systems with composition 20SrO-5CaO-40Li2O-(35-x) B2O3-x Eu2O3 (x = 0.3, 0.5 and 1 mol%) glasses were prepared by melt quenching technique to study absorption and luminescence properties and understand their lasing properties. Thepresent work reports the studies on Physical, Optical and luminescence properties of the prepared glass systems. The photoluminescence (PL) intensity of the glass increases with increase in Eu2O3 content up to 1mol%. The increase in the density and decrease in molar volume reveals the close packing of glass network. For Eu3+ emission the most intense red emission has been observed at the wavelength of 614nm for the transitions5D0 →7F2. The phonon energy was measured from phonon side band spectra which showed 1280cm−1, typical value for the borate glasses. Luminescence intensity ratio and lifetime analysis has been measured and discussed in the present work. The present glasses are very near to reddish orangeregion and thus can be key entrant for optical display device applications.

Effect of sodium oxide and sodium fluoride in gadolinium phosphate glasses doped with Eu2O3 content

Sodium gadolinium phosphate oxide and sodium gadolinium oxyfluoride glasses doped with europium oxide were synthesized by melt-quenching method. The density, molar volume and refractive index of the glass samples were carried out. Density and molar volume of oxide glass is more than oxyfluoride glass. The average phosphate to phosphate distance for oxide glass seems to be more than oxyfluoride glass. Polaron radius, inter-ionic radius shows 1.181 nm, 2.88 nm and 1.174 nm, 2.86 nm for oxide glass and oxyfluoride glasses respectively. Oxide electronic Polarizability and optical basicity of the oxide glass are lower than oxy-fluoride glass. Theoretical optical basicity shows higher for oxide glass than oxyfluoride suggesting increase in covalency of the cation to oxygen bonds in oxide glass. Optical band gap was estimated and found to be 3.061eV and 3.204 eV for oxide and oxyfluoride glass. Theoretical two photon absorption coefficient β were evaluated and found to be 11.96 and 10.80 for oxide and oxyfluoride glasses respectively. Electron-phonon coupling strength were evaluated from the phonon side band spectra for the oxide and oxy-fluoride glasses. The asymmetry ratio (R) show higher for NaF doped glass than Na2O confirming their role in elevated ionicity for oxyfluoride glass than oxide glass. Furthermore, the glasses were subjected to study for their luminescence properties of the oxide and oxyfluoride glass samples.

Novel radar signal to efficiently utilise spectrum based on continuous‐phase frequency‐shift keying

Aiming at the problem of high side-band spectrum for a general frequency-shift keying (FSK) radar signal, this study introduces a novel radar FSK signal based on continuous-phase frequency-shift keying (CPFSK) used in communication systems. Theoretical analysis, simulation and physical application results show that the CPFSK radar signal efficiently controls the spectral containment, whose roll-off performance of the CPFSK is ∼20 dB better than that of normal FSK; meanwhile, the modified signal possesses good ambiguity and pulse compression performances for radar application.

Judd–Ofelt Parameters of Eu3+ and Energy Transfer of Ce3+/Eu3+ in Sr2Al2SiO7 Materials

Sr2Al2SiO7 (SAS) phosphors doped with Eu3+, Ce3+, Ce3+/Eu3+ ions were synthesized by solid-state reaction heating at 1250°C. The phonon energy associated with the 7F0 → 5D2 transition of Eu3+ ions in SAS material was determined by phonon sideband spectra, and vibration energies in the 200–1200 cm−1 region were measured from the Raman spectra. The asymmetry of the Eu3+ site in the SAS lattice was estimated by the Judd–Ofelt intensity parameters analysis. Ωλ (λ = 2, 4, 6) intensity parameters determined from emission spectra showed that the introducing of Al2O3 leads to an enhancement of the asymmetry of the Eu3+ surroundings in SAS:Eu3+ materials. Photoluminescence investigation of SAS:Ce3+ (x mol%),Eu3+ (1 mol%) (x = 0, 0.5, 1.0, and 1.5) samples indicated that there is an energy transfer from the sensitizer Ce3+ to the activator Eu3+ in the Sr2Al2SiO7 host lattice.

Molecular dynamics simulation and luminescence properties of Eu3+ doped molybdenum gadolinium borate glasses for red emission

The contribution reports on molecular dynamics simulation were used to understand, at the molecular level, the interaction of molybdenum, gadolinium and europium ions with neighboring oxygen. Molecular dynamics simulations were carried out to evaluate the bond distance between Gd–Eu and Mo–Eu and found that the Gd–Eu bond distance is larger than for Mo–Eu. Various spectroscopic characterizations were employed to comprehend their optical and structural properties for their interconnectivity. Computational analysis was employed which emphasizes the radial distribution functions and their co-ordination numbers around Gd, Mo and Eu atoms. Phonon Side Band (PSB) spectrum associated with 7F0→5D2 transition of Eu3+ ions confirms the phonon energy of the prepared glass which was reconfirmed with FTIR and Raman spectra. The oscillator strength with and without thermal corrections was calculated from absorption spectrum to evaluate Judd-Ofelt (JO) analysis and JO parameters were estimated for 0.5 mol% Eu2O3 doped 25MoO3–20Gd2O3–(55-x)B2O3 glasses. Radiative properties such as transition probabilities, stimulated emission cross-sections and branching ratios were estimated by using JO parameters and luminescence spectra. The decay time and CIE coordinates have been calculated for prepared glass samples.

Optical and luminescence characteristics of europium doped barium lithium fluoroborate glasses

This is a report on the synthesis and spectroscopic study of europium doped barium lithium fluoroborate glasses (Eu3+:BLFB) by conventional melt quenching technique and their structural and luminescence characteristics. The X-Ray diffraction result confirms the amorphous nature of the glasses. The Judd-Ofelt parameters (Ω2, Ω4, Ω6) were calculated from the emission spectra and the trends in the intensity parameters are found to be Ω2 > Ω4 > Ω6. The JO parameters were used to predict the radiative properties like transition probability, branching ratio, radiative lifetime and stimulated emission cross section for all the emission levels of europium (Eu3+) ions. Phonon energy (1228 cm−1) have been calculated from the phonon side band spectra. From the emission spectra, fluorescence intensity ratio (R), color chromaticity values were calculated and x, y parameters which indicates the emission of red color, as observed in the in the CIE diagram. The nature of decay profiles of 5D0 state of Eu3+ in all glasses were measured and were compared with the calculated lifetimes.

Parity-time-symmetry–enhanced sideband generation in an optomechanical system

Optical high-order sideband generation, creating new frequencies with equal spectral separation, has developed potential applications in optical communication and metrology. Here, we investigate the generation of optomechanically induced high-order optical sideband spectra in an optical parity-time ($\mathcal{PT}$) -symmetric system. The system consists of an active optical mode, a passive optical mode, and a mechanical mode, where the mechanical mode is optomechanically coupled with the passive optical mode. Based on numerical analysis, the $\mathcal{PT}$-symmetric system enhances sideband spectra in both amplitude and number of sidebands. With certain parameters, forty sidebands head up on both sides of the control field near the exceptional point. The capability to generate optical high-order sidebands and control light propagation in micro- and nanomechanical systems may open up a promising perspective for complex integrated $\mathcal{PT}$ devices.

Evaluation of resonance phenomena of mechanical oscillator by self-mixing solid-state laser Doppler vibrometry.

We performed self-mixing laser Doppler vibrometry on a vibrating oscillator consisting of a rigid-body laser-light-scattering object attached to a piezoelectric element driven by low-frequency AC voltage to evaluate its motion. The sideband spectrum reflecting the motion of the oscillator is observed in the power spectrum of the modulated wave. The time dependence of the intensity of the sideband spectrum is explained by Newton's second law assuming that the oscillator has a mechanical resonance frequency and undergoes simple vibration under the driving force, which depends on the deformation velocity of the piezoelectric element. Our results indicate that the motion of a slowly moving target with sub-nanometer displacement, which is difficult to measure by general laser Doppler vibrometry, can be evaluated with high spatial and frequency resolutions by detecting the sideband signal, which changes periodically at the driving frequency of the piezoelectric element.

Difference frequency sideband generation in semiconductors

In this paper, a near-infrared (NIR) laser (with frequency ωNIR) exciting and an intense mid-infrared (MIR) bichromatic laser (with frequencies ω1 and ω2) driving scheme is proposed in semiconductors. It is predicted that if the frequency difference between the two components of the MIR laser, i.e. Ω = ω1-ω2, is in dozens of GHz frequency range, the emitting light contains spectra with frequencies ω = ωNIR + NΩ, where N is integer. In analogy with high-order THz sideband generation (HSG) in semiconductors, this phenomenon is named difference frequency sideband generation (DSG). Similar to the HSG case, the emitted sideband spectrum in DSG exhibits a nonperturbative plateau, where the intensity of the sideband remains approximately constant up to a cutoff frequency. The location of the cutoff frequency and its relationship with the frequency detuning of the NIR laser are discussed via the semi-classical saddle-point method.

Photoluminescence characteristics and energy transfer mechanism of Eu3+:NaY(WO4)2 microparticles

A series of red emitting phosphors Eu3+:NaY(WO4)2 were successfully synthesized through conventional hydrothermal reactions. Meanwhile, the photoluminescence characteristics of Eu3+:NaY(WO4)2 microparticles were detailedly discussed. The XRD measurements demonstrate that all products exhibited pure phase as NaY(WO4)2 and doping Eu3+ ions did evoke change the crystal parameters of matrix material. The SEM and TEM images show that the particle morphology was quasi-cubes with uniform appearance and the size was about 3–4 µm. Microparticles of Eu3+:NaY(WO4)2 can observe emissions located at 594 nm and 618 nm while excited by near-UV (249 nm) and near-IR (797 nm). And the energy transfer mechanism between Eu3+ was proved to be electric dipole–dipole (d–d) interaction as well as the critical distance was calculated to be 9.936 A. What’s more, the phonon sideband spectra of Eu3+ ions was used to calculated Huang-Rays factor and analyze the phonon energy. Subsequently, for self-generated quenching process of Eu3+ occurs was well explained according to Auzel’s theoretical model. Besides, the CIE color coordinates of Eu3+:NaY(WO4)2 phosphors exhibited the ideal red chromaticity.

Effect of B2O3 content on Eu3+−Surrounding in the system SrO−x.B2O3 containing Eu3+ ions prepared by combustion method

The change of Eu3+− surrounding in the system SrO−x.B2O3 with various x values (x = 0.33, 0.5, 1) synthesized by combustion method was investigated via photoluminescence (PL) spectra and phonon sideband (PSB) spectra. From the analysis of PSB spectra, it is reasonable to suggest that when increasing B2O3 content the electron−phonon coupling strength increases due to the increase in the number of BO− non−bridging bond. By using Judd−Ofelt (JO) theory for PL spectra of Eu3+ ion, the Ω2 intensity parameter was calculated and it also shows the asymmetry of Eu3+− surrounding increase corresponding to the B2O3 content.

Raman and photoluminescence studies of europium doped zinc-fluorophosphate glasses for photonic applications

Europium (Eu3+)-doped zinc-fluorophosphate (PKAZfEu) glasses have been synthesized by usual melt-quenching technique. Optical absorption, photoluminescence excitation, photoluminescence and decay curves of these glasses were measured at room temperature and investigated. The Judd-Ofelt (JO) parameters (Ωλ, λ = 2 and 4) were determined from the measured emission spectra and used for quantifying the radiative parameters that include radiative transition probability (AR), radiative lifetime (τR), branching ratios (βR), effective bandwidths (∆λeff) and peak stimulated emission cross-section (σ(λP)) for the 5D0 luminescent state of Eu3+. The electron-phonon coupling strength and phonon energy of the glasses were obtained from the phonon sideband spectrum. The chromaticity coordinates for different concentration of PKAZfEu glasses were evaluated by analyzing the emission spectra with Commission International de l'Eclairage (CIE) color diagram. Decay curves of Eu3+ ions for the 5D0 → 7F2 transition have been obtained under 393 nm excitation. The decay curves exhibit a single exponential behavior for all the investigated glasses. Luminescence properties of Eu3+ ion for the 5DO → 7F2 transition indicate that the PKAZfEu glasses could be a suitable gain medium for visible red lasers and display devices.

Strongly inhomogeneous distribution of spectral properties of silicon-vacancy color centers in nanodiamonds

The silicon-vacancy (SiV) color center in diamond is a solid-state single photon emitter and spin quantum bit suited as a component in quantum devices. Here, we show that SiV centers in nanodiamonds exhibit a strongly inhomogeneous distribution with regard to the center wavelengths and linewidths of the zero-phonon-line (ZPL) emission at room temperature. We find that the SiV centers separate in two clusters: one group exhibits ZPLs with center wavelengths within a narrow range ≈730–742 nm and broad linewidths between 5 and 17 nm, whereas the second group comprises a very broad distribution of center wavelengths between 715 and 835 nm, but narrow linewidths from below 1 up to 4 nm. Supported by ab initio Kohn–Sham density functional theory calculations we show that the ZPL shifts of the first group are consistently explained by strain in the diamond lattice. Further, we suggest, that the second group showing the strongly inhomogeneous distribution of center wavelengths might be comprised of a new class of silicon-related defects. Whereas single photon emission is demonstrated for defect centers of both clusters, we show that emitters from different clusters show different spectroscopic features such as variations of the phonon sideband spectra and different blinking dynamics.

Magnon-induced high-order sideband generation.

Magnon Kerr nonlinearity plays a crucial role in the study of an optomagnonical system and may bring many interesting physical phenomena and important applications. In this Letter, we report the investigation of high-order sideband generation induced by magnon Kerr nonlinearity in an optomagnonical system, which is still unexplored in this emerging research field. We uncover that the microwave driving field plays a significant role in manipulating the generation and amplification of the higher-order sidebands and, more importantly, the sideband spacing can be regulated by controlling the beat frequency between the pump laser and the probe laser, which is extremely eventful for the spacing modulation of the sideband frequency comb. Based on the recent experimental progress, our results will deepen our cognition into optomagnonical nonlinearity and may find fundamental applications in optical frequency metrology and optical communications.

Development of Eu3+ doped Li2O-BaO-GdF3-SiO2 oxyfluoride glass for efficient energy transfer from Gd3+ to Eu3+ in red emission solid state device application

The Eu3+- doped Li2O-BaO-GdF3-SiO2 glasses were fabricated by conventional melt quenching technique to study its spectroscopic and luminescence properties for lasing potential. The density and molar volume of the glass had been increased with Eu2O3 concentration. An FTIR spectrum is used to study the structural properties of the developed glasses. Two intense peaks were observed in UV–Vis–NIR spectra at 2206 nm (7F6) and 2085 nm (7F1) in NIR region. Under 394 nm excitation LBGFS display five regular emission peaks at (578 nm) 7F0, (590 nm) 7F1, (613 nm) 7F2, (651 nm) 7F3 and (701 nm) 7F4 from 5D0 state, the most intense red emission was found at 613 nm. The characteristic intense red emission peak at 613 nm corresponding to the 5D0 →7F2 transition of Eu3+ ions has been observed for oxy-fluoride glass samples. Efficient energy transfer phenomena from Gd3+ → Eu3+ were observed under 275 nm excitation in these glasses. FTIR measurements reveal that these glasses show non-bridging oxygen stretching of Si-O- at ~929 cm−1. Phonon sideband spectrum confirms the phonon energy ~920 cm−1 for these glasses arising from Si-O-. Increasing trend of IR/O with increasing concentration of Eu2O3 indicates the asymmetric environment around Eu3+ in LBGFS. Higher value of stimulated cross section (σ(λp)) branching ratio (βR) for transition to 7F0 from 5D0 were observed for LBGFS glasses. Decay time decrease with increasing concentration of Eu2O3.

Strong thermomechanical squeezing in a far-detuned membrane-in-the-middle system

We demonstrate 8.5 dB thermal squeezing of a membrane oscillator using the dynamical backaction effect and electrostatic feedback in an optomechanical membrane-in-the-middle setup. We show that strong squeezing can be obtained even in the far detuning regime of a sideband-resolved system. By using the dielectrophoretic force of a metallic needle kept in close proximity to the membrane, we implement the one-quadrature active feedback scheme to prevent the divergence of the amplified quadrature and surpass the 3 dB limit of mechanical squeezing. We also discuss different regions of the sideband spectrum where strong squeezing can be obtained. Although the demonstration here is classical, this technique is equally applicable to prepare the mechanical oscillator in a quantum squeezed state.

Carrier thermometry of cold ytterbium atoms in an optical lattice clock

The ultracold atomic gas serving as the quantum reference is a key part of an optical lattice clock, and the temperature of atoms in the optical lattice affects the uncertainty and instability of the optical lattice clocks. Since the carrier spectrum of the clock transition in the lattices reflects the thermal dynamics of cold atoms, the temperature of atoms can be extracted from the carrier spectrum in a non-magic wavelength lattice of ytterbium optical clocks. Furthermore, the temperatures obtained from the carrier spectra are in good agreement with the results obtained by the time-of-flight method and thermometry based on the sideband spectrum. In addition, the heating effects caused by the lattice laser are studied on the basis of the sample temperatures.

Ar 3p photoelectron sideband spectra in two-color XUV + NIR laser fields

We performed photoelectron spectroscopy using femtosecond XUV pulses from a free-electron laser and femtosecond near-infrared pulses from a synchronized laser, and succeeded in measuring Ar 3p photoelectron sideband spectra due to the two-color above-threshold ionization. In our calculations of the first-order time-dependent perturbation theoretical model based on the strong field approximation, the photoelectron sideband spectra and their angular distributions are well reproduced by considering the timing jitter between the XUV and the NIR pulses, showing that the timing jitter in our experiments was distributed over the width of ps. The present approach can be used as a method to evaluate the timing jitter inevitable in FEL experiments.

Interrogation of spin polarized clock transition in strontium optical lattice clock

We demonstrate a spin-polarized clock transition spectrum of the 87Sr optical lattice clock. The clock transition 5s2 1S05s5p 3P0 of isotope 87Sr has a hyperfine structure due to non-zero nuclear spin, inducing ten -polarized transitions from each individual mF state under the condition of a bias magnetic field along the probing polarization axis. In this experiment, atoms are driven to a certain mF state by a circular-polarization pump light to maximize the atomic population, which is beneficial to the stability and uncertainty evaluation of the optical lattice clock. After two stages cooling and trapping, about 3.5106 atoms are trapped in the red magneto-optical trap with a temperature of 3.9 K. A grating-feedback external cavity diode laser with a tapered amplifier is used to build the optical lattice with a magic-wavelength of 813.426 nm. Both waists of the counter-propagating lattice beam along the horizontal direction are overlapped to form a one-dimensional (1D) optical lattice. The lifetime of the atoms trapped in the 1D optical lattice is 1600 ms. The clock laser at 698 nm is a grating-feedback diode laser, which is locked to an ultra-low expansion cavity by the Pound-Drever-Hall technique to stabilize the frequency and phase. As a result, the linewidth of clock laser is narrowed to Hz level. By the normalized shelving method, we obtain a resolved sideband spectrum of 87Sr 5s2 1S05s5p 3P0 transition. According to the spectrum, the lattice temperature along the longitudinal direction is approximately 4.2 K. After that a linewidth of 6.7 Hz of the degenerate clock transition is obtained at a probing time of 150 ms by utilizing a three-dimensional (3D) bias magnetic field, which is used to eliminate the stray magnetic fields. Then a small bias magnetic field of 300 mGs is applied along the polarization axis of the lattice light to achieve the spectrum of Zeeman magnetic sublevels of the clock transition. Furthermore, the mF=+9/2 and mF=-9/2 magnetic sublevels are picked to be respectively pumped by the +-polarized and --polarized light at 689 nm, a variable liquid crystal wave plate is employed to switch on both polarizations. Finally, the spin polarized clock transition spectrum is obtained at the interrogating pulse of 150 ms, and the linewidths of the mF=+9/2, mF=-9/2 magnetic sublevel transitions are 6.8 Hz and 6.2 Hz respectively.

Quadrature squeezing of a higher-order sideband spectrum in cavity optomechanics.

We propose an efficient scheme to generate quadrature squeezing of a higher-order sideband spectrum in an optomechanical system. This is achieved by exploiting a well-established optomechanical circumstance, where a second-order nonlinearity is embedded into the optomechanical cavity driven by a strong control field and a weak probe pulse. Using experimentally achievable parameters, we demonstrate that the second-order nonlinearity intensity and the frequency detuning of a control field allow us to modify the amplitude of higher-order sidebands and improve the amount of squeezing of a higher-order sideband spectrum. Furthermore, in the presence of a strong second-order nonlinearity, an optimizing quadrature squeezing of a higher-order sideband spectrum can be achieved, which provides a practical opportunity to design the squeezed frequency combs and other precision measurements.