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This work proposes and experimentally demonstrates a high-performance polarization space parity-time (PT) symmetric fiber ring laser to achieve a low-noise, narrow-linewidth, and highly stable single-longitudinal-mode output. The gain/loss and coupling coefficients are regulated by adjusting a polarization controller (PC) and the pumping current of an erbium-doped fiber amplifier (EDFA) within the ring cavity. The results show that the single longitudinal mode oscillation of the laser can be implemented by PT symmetry breaking. The frequency noise spectral density and the linewidth characteristics of the laser are evaluated by the short-delay self-heterodyne method. The results reveal that excellent low-frequency noise (181 Hz2/Hz at a 10 kHz offset frequency) and narrow fundamental linewidth (68 Hz) can be achieved. Additionally, the laser exhibits outstanding stability with only 0.64 pm wavelength drift over 30 min. By tuning an optical tunable filter (OTF), the wavelength tunable range of the laser can cover the entire C-band. Furthermore, the impacts of different fiber length on the frequency noise spectral density and the filter bandwidth on stability are analyzed, offering guidance for component selection in such laser systems. [ABSTRACT FROM AUTHOR]

We propose and experimentally investigate a symmetric parity-time (PT) coupled optoelectronic oscillator (COEO) based on a polarization-dependent spatial structure. In such a COEO system, the gain/loss and coupling coefficients of two orthogonal polarization optical waves can be controlled by adjusting the polarization controller (PC) and the bias voltage of a Mach-Zehnder modulator (MZM). The single-mode selection of a microwave signal can be implemented by the PT symmetry breaking of a special mode. The performance of the proposed COEO is experimentally examined, and a 10.0 GHz microwave signal with a phase noise of −109.1 dBc/Hz @ 10 kHz and a side mode suppression ratio of 51.4 dB is generated. Moreover, an optical frequency comb with a comb tooth spacing of 10.0 GHz and a bandwidth of 100 GHz within a 10 dB amplitude variation can be simultaneously generated. [ABSTRACT FROM AUTHOR]

This work proposes and experimentally demonstrates a high-performance polarization space parity-time (PT) symmetric fiber ring laser to achieve a low-noise, narrow-linewidth, and highly stable single-longitudinal-mode output. The gain/loss and coupling coefficients are regulated by adjusting a polarization controller (PC) and the pumping current of an erbium-doped fiber amplifier (EDFA) within the ring cavity. The results show that the single longitudinal mode oscillation of the laser can be implemented by PT symmetry breaking. The frequency noise spectral density and the linewidth characteristics of the laser are evaluated by the short-delay self-heterodyne method. The results reveal that excellent low-frequency noise (181 Hz2/Hz at a 10 kHz offset frequency) and narrow fundamental linewidth (68 Hz) can be achieved. Additionally, the laser exhibits outstanding stability with only 0.64 pm wavelength drift over 30 min. By tuning an optical tunable filter (OTF), the wavelength tunable range of the laser can cover the entire C-band. Furthermore, the impacts of different fiber length on the frequency noise spectral density and the filter bandwidth on stability are analyzed, offering guidance for component selection in such laser systems.

We propose and experimentally investigate a symmetric parity-time (PT) coupled optoelectronic oscillator (COEO) based on a polarization-dependent spatial structure. In such a COEO system, the gain/loss and coupling coefficients of two orthogonal polarization optical waves can be controlled by adjusting the polarization controller (PC) and the bias voltage of a Mach-Zehnder modulator (MZM). The single-mode selection of a microwave signal can be implemented by the PT symmetry breaking of a special mode. The performance of the proposed COEO is experimentally examined, and a 10.0 GHz microwave signal with a phase noise of −109.1 dBc/Hz @ 10 kHz and a side mode suppression ratio of 51.4 dB is generated. Moreover, an optical frequency comb with a comb tooth spacing of 10.0 GHz and a bandwidth of 100 GHz within a 10 dB amplitude variation can be simultaneously generated.

A polarization-based laser resonator cavity with continuous variable output coupling is investigated using Cr:forsterite crystal as the gain medium. The confocal resonator cavity houses intracavity polarization optics for continuous tuning of the output coupler. The variation in the coupling efficiency is suitably explained by calculation based on Jones matrix formalism. The established resonator cavity is found to be advantageous for fine control over the cavity output energy, intracavity energy, cavity buildup time, laser pulse width, and threshold pump energy. The theoretically estimated output energy is in good agreement with the experimental results. The investigated system provides flexible optimization of the laser parameters and can be useful for all optical synchronization of multiple laser pulses as desired in many spectroscopic experiments. [ABSTRACT FROM AUTHOR]

The results of a study of pulse duration of superradiance on molecular nitrogen ions in air under different conditions of focusing a femtosecond laser pulse with a wavelength of 950 nm are presented. The active-medium parameters are analyzed and a mechanism is proposed for formation of a picosecond superradiance pulse at a femtosecond seed-pulse duration. [ABSTRACT FROM AUTHOR]

Thulium (Tm3+)-doped boro-tellurite glasses were prepared by melt-quenching technique and their optical, photo-luminescence (PL), and time-resolved spectroscopic behaviors were studied. The Judd-Ofelt (J-O) parameters were calculated from the absorption spectra and evaluated the radiative factors for emission transitions. The PL and up-conversion (UC) emission spectra were measured under the excitation wavelengths of 473, and 793 nm diode lasers, respectively. The emission peak of 3H 4 →3H 6 (793 nm) and up-conversion 3F 2,3 → 3H 6 (696 nm) transitions shifted to higher wavelengths with the increment of Tm 2 O 3 concentration, while the 1G 4 →3F 4 (650 nm), 3H 4 →3F 4 (1466 nm) and 3F 4 →3H 6 (1821 nm) transitions showed no change in peak positions, under 473 nm laser excitation. The time-resolved spectroscopic measurements are recorded and analysed for all transitions. Under 793 nm laser, NIR emission spectra (1200–2200 nm) and spectroscopic characteristics were measured to discuss the energy transfer mechanisms. The strong transitions of 3H 4 →3F 6 (1466 nm) and 3F 4 →3H 6 (1821 nm) were observed and corresponding emission cross-section and gain factors have been evaluated and discussed for the application of the S-band communication window. • Tm3+ concentration-dependent borotellurite glasses were synthesized. • Structural and optical characteristics were studied and discussed. • Judd-Ofelt intensity parameters were evaluated and compared. • Photoluminescence and upconversion emission features were investigated. • The present glass showed high NIR emission cross-section at 1.8 μm. [ABSTRACT FROM AUTHOR]

For 3 p 6 3 d 4 l where l = s , p , d , f states in Ni + 8 , we evaluated both oscillator strengths and energy levels to investigate the probability of laser wavelengths production in the soft X-ray and XUV regions. The calculations are executed using CIV3 and LANL codes. By comparing the values of our results with other published experimental and theoretical data, a good match is achieved in addition to unpublished values of oscillator strengths and energy levels have been obtained. Using calculated oscillator strengths, the gain coefficients, and reduced populations have been calculated for Ni + 8 at different plasma temperatures, such as T = 1 / 4 the ionization potential energy (IP) of the Ni + 8 ; and the same thing for T = 1 / 2 I P and T = 3 / 4 I P . Promised values of positive laser gain are shown to obtain laser wavelengths in XUV and soft X-ray regions from current computed atomic data. Extreme ultraviolet radiation XUV is electromagnetic radiation in the part of the electromagnetic spectrum spanning wavelengths from 124 nm down to 10 nm. [ABSTRACT FROM AUTHOR]

• Findlay-Clay method are formalized and used in quasi-three-level lasers. • Gain coefficient and resonator internal loss are measured in thin-disk laser. • The results are compared with spectroscopic gain analysis (SGA). • Measurements are evaluated by a numerical analysis. • SGA leads to less error in measurement of gain coefficient respectively. In this paper, the gain coefficient and the resonator internal loss in quasi-three-level active medium lasers were measured by two different methods: the spectroscopic gain analysis (SGA) and generalized Findlay-Clay method (GFCM). Standard Findlay-Clay method was modified and formalized for quasi-three-level active medium lasers. With these methods, the gain coefficient and the resonator internal loss of a Yb:YAG thin-disk-laser (TDL) were obtained and the results were compared, analyzed and discussed. To verify the accuracy of these methods, a numerical code based on the laser rate equations was developed to simulate the cw operation of the TDL and predict the laser system parameters. The obtained values of the resonator internal loss from these methods were used in the simulation to calculate some laser parameters such as laser output power and gain of the active medium. The analyses of measured values showed that the results of SGA have better accuracy. The relative measurement errors of 1.2% and 18.4% for gain coefficient were obtained for SGA and GFCM, respectively. [ABSTRACT FROM AUTHOR]

The paper presents experimental study of the major erbium-doped fibre amplifier (EDFA) features such as gain at low signal and gain saturation by an application of different erbium-doped optical fibres (EDFs). The main objective of the research is to estimate how the performance of EDFA varies depending on the length of doped fibre, pumping configuration scheme, as well as excitation source power. It is shown that a high gain coefficient of 16–20 dB can be practically achieved. [ABSTRACT FROM AUTHOR]

Concealing the time delay signature and enhancing the complexity of electro‐optic (EO) chaotic system is important for practical applications. Therefore, in this study, the authors propose a new coupled EO chaotic system based on the classical one. In the new model, the electrical signals are mixed by using nonlinear coupling functions. Some simulation experiments are used to illustrate its chaotic performances and complexity. All results indicate that the new coupled model has a high complexity level, and can be competitive to other proposed EO systems. Furthermore, the time‐delay signature can be effectively concealed with a smaller gain coefficient than other systems. All these results demonstrate that this new system is more potential to be used in random number generation and chaotic secure communication. [ABSTRACT FROM AUTHOR]

Influence of various design data of jet controls (amount of jets, a direction of injection, geometrical characteristics of nozzles, their mutual position, etc.) on flow structure and flying vehicles aerodynamic characteristics is defined and recommendations on optimum use of jet injection as a way of control of flow near flying vehicles are developed.

Highlights • A series of germanium-doped Yb: phosphate glasses were prepared. • The structure and spectroscopic properties of this novel glass were investigated. • These novel glasses have large gain coefficient and systematical factor (SFL), compared to traditional phosphate glasses. Abstract Germanium dioxide (GeO 2)-doped phosphate glasses with large gain coefficient and systematical factor (SFL) were prepared by high temperature melting for laser glass applications. Their physical parameters and optical properties were investigated such as glass transition temperature (Tg), density, Raman spectra, fluorescence emission spectra, decay cure and absorption spectra. Compared with the traditional phosphate glass, the introduction of GeO 2 to phosphate glass results in a high fluorescent intensity and a long lifetime. All these advantages might mean that GeO 2 -doped phosphate glasses are a promising candidate as a gain medium for ultra-fast and high-power laser. [ABSTRACT FROM AUTHOR]

Er 3+ -ions doped lithium‑bismuth-boro-phosphate glass samples were prepared by conventional melt quenching method and their structural, thermal, fluorescence, and decay times of the glasses were investigated. Prepared glass samples exhibits amorphous nature and shows very good thermal stability in the temperature range of RT to 500 °C. Judd-Ofelt (JO) analysis was carried out to obtain the parameters which will evidence the glass system for fibre and lasing applications. The intensity parameters Ω λ(2,4 and 6) and stimulated-emission cross-sections were estimated for present glass system. The magnitude of Ω 2 confirms the covalency nature and compared with available other host. The near infrared emission spectra were measured by 980 nm excitation in which the emission intensity is found to be at 1532 nm for the 4 I 11/2 – 4 I 15/2 transition. The FWHM (78 nm), σ(λ p ) (10.11 × 10 −21  cm 2 ), ΔG (7.93 × 10 −28  cm 3 ) and G (9.1 × 10 −24  cm 2  s), for 4 I 11/2 – 4 I 15/2 transition of present glasses are compared to some of the glass systems. Furthermore, the time decay rate found to be slight decreased from 1.04 ms to 0.90 ms when the concentration increased from 0.1 to 0.5 mol% of Er 3+ ions and also all follow the single exponential behaviour which is attributed to the self-quenching effect due to the cross-relaxation channels. McCumber's theory reveals peak emission cross-section value is also good agreement with σ(λ p ) which is 10.11×10 −21 cm 2 . The obtained gain coefficient population inversion 40% with broad band of emission proves to consider the present system for C band amplifiers. The up conversion of luminescence spectra upon 980 nm excitation exhibits red emission at 665 nm due to 4 F 9/2 - 4 I 15/2 transitions also two photon absorption was obtained for power dependence up conversion. [ABSTRACT FROM AUTHOR]

A novel coupled electro‐optic delayed feedback chaotic system is proposed and studied here. Both electrical coupling and optical coupling are used in this model, where electrical coupling is mainly used to suppress the time‐delay signature, and optical coupling is mainly used to improve its complexity. The dynamical performances and complexity are demonstrated, and the simulation results show that the complexity of this model has been greatly improved. Moreover, the time‐delay signature cannot be recognised with a low gain, and the suppress effect will be enhanced by increasing the gain coefficient. Comparing with other recently proposed models, the authors model is competitive in security, and has potential applications in secure communication and random number generation. [ABSTRACT FROM AUTHOR]

In this article, the lasing characteristics of a dye Neutral Red in spectroscopic grade ethanolic solutions is reported. The lasing emission spectra for a dye concentration of 0.35 mg/L were studied using an Nd: YAG laser operating at a wavelength of 532 nm. The absorption peak and emission peak of the dye was found to be at 533 nm and 614 nm respectively. The quantum yield of the dye was calculated to be 0.8. The dye exhibited better photostability with a low lasing threshold of 8.8 mJ and a gain coefficient of 31 cm −1 . The lifetime of the dye obtained was 9.7*10 −10  s. From the present study, we came to a conclusion that the dye under study is a much promising candidate for lasing applications. [ABSTRACT FROM AUTHOR]