A uniform formulation for the self-imaging of gratings with any kind of partially coherent illumination is developed in terms of the cross mutual spectral density of the partial coherence theory. The formulation includes the time diffractive intensity distribution and the averaged diffractive intensity distribution at self-imaging distances and can be applied to both continuous and temporal illuminations with any kind of spectra. It is found that the averaged intensity distribution is related only to the intensity spectrum of illumination. The continuous polychromatic illumination and the ultrashort laser pulses with or without frequency chirp are then studied by a numerical stimulation. It is shown that the ultrashort laser pulse and the continuous polychromatic illuminations have similar averaged self-image distributions. Thus the Talbot effect may help in the study of the temporal and spectral characteristics of ultrashort laser pulses. An experiment with an LED is given, as well.
An oscillatory characteristic of diffraction is observed as a result of strong beam coupling in a weakly oxidized LiNbO3:Ce:Cu crystal during the recording step in the production of nonvolatile photorefractive holograms. On this basis the optimal switching time from the recording step to the fixing step for high diffraction of a fixed hologram is studied. It is shown that switching after the first diffraction maximum leads theoretically to fixed diffraction of as much as 100% with a suitable switching time. Both an experimental demonstration and a theoretical simulation are presented.
at the sintering temperature of 1,273 K. By a 978 nm semiconductor laser diodes excitation, the visible up-conversion emissions centered at about 523, 545, and 660 nm were obtained. The temperature dependence of the green up-conversion emissions was studied over a wide temperature range of 300-825 K, and the reasonable agreement between the calculated temperature by the fluorescence intensity ratio (FIR) theory and the measured temperature proved that Er 3+ -Yb 3+ codoped Al 2 O 3 plays an important role in the application of high temperature sensor.
Based on the finite-difference method, a typical Tm-doped double-clad fiber amplifier modeling is comprehensively analyzed through the rate equations and propagation equations. The impacting factors such as amplified spontaneous emission (ASE), wavelength and power of the seed, fiber length, pumping power and fiber facet reflectivity are discussed. Simulation results show that there exist the most suitable fiber length and pump power while the amplifier has the maximum output power and the best signal to noise ratio. Moreover, the influence of ASE can be effectively inhibited by reducing the fiber facet reflectivity, especially the front fiber facet reflectivity, choosing the proper seed wavelength and increasing the seed power. The theoretical models and simulation results presented in this paper have a certain reference value for the design and development of high-power Tm-doped double-clad fiber amplifiers.Keywords-tm-doped fiber; fiber amplifier; numerical modeling; amplified spontaneous emission
Ⅰ. INTRODUCTIONRecent years, there has been growing interests in high power Tm-doped fiber lasers and amplifiers operating in eye-safe wavelength around 2um,due to its widely applications in optical spectroscopy, gas sensing, lidar, telecommunications and laser surgery [1][2]. For some of these applications, high output power or energy as well as narrow linewidth and good beam quality are required. One promising way to realize these performance specifications is via the use of a master-oscillator power -amplifier (MOPA) system [3][4].Theoretical modeling and simulations are important to investigate characteristics of lasers and amplifiers and then optimize parameters for practical system. For the Yb-doped fiber lasers and amplifiers, a lot of theoretical models have already been proposed [5][6][7]. Compared with Yb-doped fiber operated in the 1um region, Tm-doped fiber has a much larger nonlinear threshold and much broader gain bandwidth promising to offer much higher laser output than currently widely used Yb-doped fiber. However, there are just a few theoretical models of Tm-doped fiber lasers reported and the influence of amplified spontaneous emission (ASE) is not considered in these models [8][9]. A systematic investigation of Tm-doped fiber double-clad (TDDC) fiber amplifier has not been presented to the best of the author's knowledge.In this paper, targeting the characteristics and optimization of continuous wave TDDC fiber amplifier, from the rate equations and propagation equations, a typical TDDC fiber amplifier model is comprehensively analyzed through finite-difference method. The impacting factors such as ASE, wavelength and power of the seed, fiber length, pumping power and fiber facet reflectivity are discussed. The theoretical model and simulation results presented in this paper have a certain reference value for the design and development of high-power TDDC fiber amplifiers.
Ⅱ. AMPLIFIER CONFIGURATION AND THEORETICAL MODELINGSimilar to the Yb-doped fiber amplifier model [10], a bidirectionally pumped...
A narrow-linewidth 793-nm diode-pumped Tm 3þ -doped double-clad silica fiber laser operated at 2 m and actively Q-switched with an acousto-optic modulator is reported. Using a fiber Bragg grating as an output coupler, approximately 0.1-nm linewidth at 1996.8-nm pulses is derived at 80-kHz repetition rate. The maximum average output power is above 2 W for 11.6-W absorbed pump power. Less than 150-ns pulse is obtained at the repetition rate of 30 kHz. The laser is a promising seed laser for amplification in a master oscillator power amplifier system.
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