Influence Of Energy-transfer Upconversion Research Articles

Influence of upconversion transition process on the performance of inband pumped holmium-doped silica fiber amplifiers

In this report, a theoretical model of in-band pumped holmium-doped silica fiber amplifiers (HDFAs) is presented. This model is developed to consider the influence of energy transfer up-conversion (ETU) on the HDFAs performance. The advantage of this model is to investigate the properties of HDFAs as a function of holmium-doped fiber length and doping concentration. A good agreement is observed between the simulation results and the previous experimental findings. Our simulation results show the negative impact of ETU process to deteriorate the HDFAs performance and this process may have bigger effect at high holmium doped concentration. This is the first time to our knowledge that the influence of upconversion process is theoretically investigated on the performance of in-band pumped HDFAs.

Investigation into the thermal effects of a Nd:YVO4 crystal at 1342 nm using the bistability-like output characteristics

The influence of energy-transfer upconversion (ETU) and excited stimulated absorption (ESA) on the thermal effects of a Nd:YVO4 crystal was investigated in this paper. A stable continuous-wave (CW) single-frequency and intracavity frequency-doubled dual-wavelength 1342/671 nm laser was built, and the output power was manipulated by changing the transmissions of the output coupler. When the output coupler coated with a partial transmission film of 0.5% at 1342 nm was replaced by that of 8% at 1342 nm, the maximum output powers of the 671 nm and 1342 nm lasers ranged from 3.35 W and 1.08 W to 0.43 W and 6.35 W, respectively. By accurately measuring the threshold pump power as the incident pump power increased, a thermal loading of 6.8% caused by the ETU was successfully determined, which was the same for both output couplers. However, the thermal loading caused by the ESA had to be determined by measuring the threshold as the incident pump power decreased, and the measured thermal loading caused by the ESA was 14.03% for the output coupler with a transmission of 0.5%, which was larger than that of 9.13% for the transmission of 8% at 1342 nm. The measured results depicted that the thermal loadings caused by the ETU and ESA depended on the pump power and intracavity power of the 1342 nm laser, respectively. This technique for determining the thermal loadings of the Nd:YVO4 at 1342 nm using the bistability-like output characteristics is a good method of evaluating the thermal loadings and thermal lens effects of other laser crystals.

Influence of energy-transfer upconversion and excited-state absorption on a high power Nd:YVO4 laser at 134 μm

A self-consistent theoretical model considering both energy-transfer upconversion (ETU) and excited-state absorption (ESA) effects, as well as the couplings among the temperature distribution in the laser crystal, the thermal fractional loading, the upper state population involved in the ETU and ESA effects, the laser output and other temperature-dependent parameters, was developed to simulate the behaviors of diode-end-pumped continuous-wave (CW) single-transverse-mode (TEM00) lasers. Based on the theoretical and experimental investigations of the influences of ETU and ESA effects on laser performance, a high power CW TEM00 Nd:YVO4 1.34 μm laser dual-end pumped at 880 nm was achieved with a maximum output power of 16 W. The measured laser beam quality was M2x = M2y = 1.17 and the stability of the laser output was better than ± 0.9% in a given four hours. The theoretical predictions considering both ETU and ESA effects are in good agreement with experimental results.

The influence of energy transfer upconversion on Q-switched single resonator optical parametric oscillator

The influence of energy transfer upconversion on Q-switched single resonator intracavity optical parametric oscillator is investigated by a space-dependent rate equation model. The numerical analysis shows that the energy transfer upconversion effect causes the pump size to have an optimum for yielding the largest output power at a given pump power. To verify the presented model, the practical example of Q-switched Nd : YVO4—KTA single resonator intracavity optical parametric oscillator has been used. The optimum pump size, calculated by presented model is 320 μm which is reported 300 μm.

The influence of energy transfer upconversion on thermal loading in end-pumped Nd:GdVO4 laser

The influence of energy transfer upconversion on thermal loading in end-pumped Nd:GdVO4 laser was investigated. The dependence of thermal loading on absorbed pump power and pump radius was discussed. Higher absorbed pump power and smaller pump radius resulted in more serious ETU effect, which cause more extra thermal loading. The experimental results indicated that ETU effect in Nd:GdVO4 laser is a unneglectable mechanism to generate extra heat especially in end-pumped geometry

The effects of energy transfer upconversion on end-pumped Q-switched Tm, Ho : YLF lasers

Based on the model of continuous wave end-pumped quasi-three-level system, the influence of energy transfer upconversion (ETU) on diode-end-pumped actively Q-switched Tm, Ho : YLF lasers is investigated by the rate equation analysis. The analytical expressions of the fractional thermal loading and the pulse energy are obtained. The influences of ETU on the fractional thermal loading and the output pulse energy are analysed. The theoretical results show that the ETU reduces not only the pulse energy but also the effective upper level lifetime of the actively Q-switched Tm, Ho : YLF laser. The practical example of the diode-end-pumped Q-switched Tm, Ho : YLF laser has been used to verify the present model.

Heat generation and thermal lensing in end-pumped Tm,Ho : YLF laser crystals

Thermal lensing in an end-pumped Tm,Ho:YLF laser crystal has been investigated with a theoretical model of continuous-wave quasi-three-level laser. Considering energy transfer upconversion (ETU) and ground-state reabsorption, the rate equations are given. The influence of ETU on the fractional thermal loading is calculated, and the results show that the latter critically depends on the pump-to-mode size ratio. The temperature distributions of a Tm,Ho : YLF crystal for different pump powers have been analysed. The output power and the focal length of the thermal lens as a function of pump power are obtained in experiment. The experimental results are compared with the theoretical results, and the experimental results show that the theoretical results are reasonable.

Theoretical and experimental study of a single frequency Tm,Ho:YLF laser

We present a theoretical and experimental analysis of a diode-pumped single frequency Tm,Ho:YLF laser. A new model for a diode-pumped Tm,Ho:YLF quasi-three-level laser is described. The influence of energy-transfer up-conversion (ETU) and ground-state re-absorption (GSA) has been taken into account. When the incident pump power is 2.8 W, a maximum single frequency output power of 118 mW is obtained from the Tm,Ho:YLF laser at room temperature. The line narrowing elements used are two solid etalons. The single frequency laser can be used as a seed laser for either a larger oscillator or an amplifier. The theoretical results are in good agreement with experimental data.

Influence of energy-transfer up-conversion on upper level lifetime of Tm, Ho:YLF Q-switched laser

Based the energy transfer between energy levels and the transition between ions of diode-end-pumped Tm,Ho:YLF laser, with consideration of energy transfer up-conversion, the rate equations of Tm,Ho:YLF Q-switched laser are given, and the analytical formulas of single pulse energy is deduced from the rate-equations. It is shown theoretically that the energy transfer up-conversion reduces not only the single pulse energy but also the upper level lifetime of Tm,Ho:YLF Q-switched laser. An experiment is carefully designed to verify these conclusions.

Q-Switched Intracavity Frequency-Doubled Solid State Lasers: Influence of ETU Effect, Repetition Rate and ESA Effect

Our theoretical analysis showed that the overall intracavity frequency-doubled actively Q-switched solid state laser performance is affected by both pulse repetition rate and energy transfer up-conversion effect. The energy transfer up-conversion effect increased greatly and seriously degraded the laser performance especially when operating at high pumping power and low pulse repetition rate. The curves generated by numerical computation of the presented model can be used to predict the laser performance. We concluded that the pulse lengthening effect also appears with the influence of energy transfer up-conversion and is not related to the repetition rate. From the analysis, we found that the frequency doubling coefficient that Liu and Kim chose in their experiment was just the optimized value. Considering the effect of excited state absorption of saturable absorber into passively Q-switched intracavity frequency doubled solid state laser, the second threshold condition for this model is derived. A simple and very clear formula is obtained.

Analysis of heat generation and thermal lensing in erbium 3-μm lasers

The influence of energy-transfer upconversion (ETU) between neighboring ions in the upper and lower laser levels of erbium 3-μm continuous-wave lasers on heat generation and thermal lensing is investigated. It is shown that the multiphonon relaxations following each ETU process generate significant heat dissipation in the crystal. This undesired effect is an unavoidable consequence of the efficient energy recycling by ETU in erbium 3-μm crystal lasers, but is further enhanced under nonlasing conditions. Similar mechanisms may affect future erbium 3-μm fiber lasers. In a three-dimensional finite-element calculation, excitation densities, upconversion rates, heat generation, temperature profiles, and thermal lensing are calculated for a LiYF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> :Er/sup 3+/ 3-μm laser. In the chosen example, the fraction of the absorbed pump power converted to heat is 40% under lasing and 72% under nonlasing conditions. The heat generation in a LiYF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> :Er/sup 3+/ 3-μm laser is 1.7 and the thermal-lens power up to 2.2 times larger than in a LiYF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> :Nd/sup 3+/ 1-μm laser under equivalent pump conditions, thus, also putting a higher risk of rod fracture on the erbium system.

Influence of energy-transfer upconversion effect on the pulse in diode-pumped Cr :YAG passively Q-switched lasers

Influence of energy-transfer upconversion (ETU) effect on the output pulse in diode-pumped Cr:YAG passively Q-switched lasers is investigated. Using the ETU theory and Q-switching rate equations, the initial population inversion, the final population inversion and the threshold population inversion at the maximum photon density are achieved. The output pulse width and pulse energy depend on the relation between them. The predicted results are in good agreement with the experimental results. The method of reducing the ETU effect is also discussed and it is useful to optimize this kind of lasers.

Modeling of diode-end-pumped Q-switched solid-state lasers: influence of energy-transfer upconversion

The influence of energy-transfer upconversion (ETU) on diode-end-pumped actively Q-switched lasers is investigated by the space-dependent rate equation analysis. The numerical analysis reveals that as a consequence of the ETU effect there is an optimum pump size for yielding the largest pulse energy and a different optimum pump for yielding the highest peak power at a given pump power. The practical example of the diode-pumped actively Q-switched Nd:YAG laser has been used to verify the present model.

Repetition-rate dependence of thermal loading in diode-end-pumped Q-switched lasers: influence of energy-transfer upconversion

The fractional thermal loading in diode-end-pumped Q-switched lasers was estimated from the theory of cavity stability. The experimental results show that the thermal loading depends on the pulse-repetition rate. This dependence is attributed to the effect of energy-transfer upconversion (ETU). A theoretical model including the ETU effect was developed to analyze the fractional thermal loading in end-pumped Q-switched lasers. The theoretical predictions were found to be in good agreement with the experimental data.

Influence of energy-transfer upconversion on the performance of high-power diode-end-pumped CW lasers

The influence of energy-transfer upconversion (ETU) on the performance of diode-end-pumped lasers is studied by including ETU effects into the space-dependent rate equations. The dependence of ETU rates on the mode-to-pump size ratio and on the output mirror transmission is derived. Experiments for Nd:YAG and Nd:YVO/sub 4/ crystals are performed to validate the present model. It is found that the ETU process increases the sensitivity of the output power to the output mirror transmission but its influence on the output power is not significant for low output transmission.