He Cai

Algorithm for evaluation of temperature distribution of a vapor cell in a diode-pumped alkali laser system: part I.

A diode-pumped alkali laser (DPAL) is one of the most hopeful candidates to achieve high power performances. As the laser medium is in a gas-state, populations of energy-levels of a DPAL are strongly dependent on the vapor temperature. Thus, the temperature distribution directly determines the output characteristics of a DPAL. In this report, we developed a systematic model by combining the procedures of heat transfer and laser kinetics together to explore the radial temperature distribution in the transverse section of a cesium vapor cell. A cyclic iterative approach is adopted to calculate the population densities. The corresponding temperature distributions have been obtained for different beam waists and pump powers. The conclusion is thought to be useful for realizing a DPAL with high output power.

Theoretical study on temperature features of a sealed cesium vapor cell pumped by laser diodes

The diode-pumped alkali laser (DPAL) is a new type of laser source which has been widely studied in the recent years. The temperature distribution of a sealed vapor cell, which is the crucial component in a DPAL system, produces an important effect on the output performance of a DPAL. In this paper, the strict solution of the heat conduction equation for a cesium vapor cell is obtained by using a finite difference procedure. The temperature distribution of a dummy open cell is first analyzed, and then the temperature distributions of two independent windows, regarded as the boundary conditions of solving a sealed cell, are evaluated in detail. By combining the results of the two steps together, we finally acquire the temperature distribution of a real sealed cesium vapor cell. The results reveal that the temperature gradients on both radial and longitudinal directions change with the pump power, cell radius, and absorption coefficient when the sealed cesium vapor cell is heated or pumped with the laser diodes. The conclusions are helpful for accurately evaluating the output characteristics of a DPAL.

Influence of energy pooling and ionization on physical features of a diode-pumped alkali laser

In recent years, a diode-pumped alkali laser (DPAL) has become one of the most hopeful candidates to achieve the high power performance. A series of models have been established to analyze the DPALs kinetic process and most of them were based on the algorithms in which only the ideal 3-level system was considered. In this paper, we developed a systematic model by taking into account the influence of excitation of neutral alkali atoms to even-higher levels and their ionization on the physical features of a static DPAL. The procedures of heat transfer and laser kinetics were combined together in our theoretical model. By using such a theme, the continuous temperature and number density distribution have been evaluated in the transverse section of a cesium vapor cell. The calculated results indicate that both energy pooling and ionization play important roles during the lasing process. The conclusions might deepen the understanding of the kinetic mechanism of a DPAL.

Investigation of physical features of both static and flowing-gas diode-pumped rubidium vapor lasers

A diode-pumped alkali lasers (DPAL) is a new type of laser source which can offer laser radiation with high efficiency and tiny thermally-induced effects in the near-infrared wavelength region. By constructing a theoretical algorithm through uniting the kinetic, heat transfer, and fluid dynamic procedures together, the thermal features and output characteristics of a DPAL are systematically evaluated for both the static and flowing-gas statuses. The corresponding temperature distributions are calculated for different powers of a pump beam. The results are thought to be useful for realization of a high-powered DPAL in the future.

Optimization of physical conditions for a diode-pumped cesium vapor laser

A diode-pumped alkali laser (DPAL) is thought to provide the significant promise for construction of high-powered lasers in the future. To examine the kinetic processes of the gas-state media (cesium vapor in this study), a mathematical model is developed while the processes including normal 3-enegry-level transition, energy pooling, and ionization are taken into account in this report. The procedures of heat transfer and laser kinetics are combined together in creating the model. We systemically investigate the influences of the temperature, cell length, and cell radius on the output features of a diode-pumped cesium vapor laser. By optimizing these key factors, the optical-to-optical conversion efficiency of a DPAL can be obviously improved. Additionally, the decrease of the output power due to energy pooling and ionization is also shrunk from 1.63% to 0.37% with the pump power of 200 W after optimization. It suggests that the effects of energy pooling and ionization should be decreased apparently under the optimal conditions. Basically, the conclusions we obtained in this study can be extended to other kinds of end-pumped laser configurations.

Analysis of characteristics of a diode-pumped rubidium vapour laser using a kinetic algorithm

We consider diode-pumped alkali vapour lasers (DPALs), which make it possible to achieve a high output power. Characteristics of such DPALs strongly depend on the physical properties of buffer gases and on structural parameters of a vapour cell. Special attention is paid to a diode-pumped rubidium vapour laser (DPRVL): We have investigated the effect of different conditions on its characteristics. The results show that the linewidth of the D2 line of a DPRVL and the fine-structure mixing rate between two excited energy levels, which are two crucial factors in implementing a high-power DPRVL, increase with the pressure of buffer gases and the temperature of the vapour cell. It is demonstrated that the population ratio of two excited energy levels is close to that corresponding to a thermal equilibrium as the pressure of buffer gases and the temperature of the vapour cell become higher. We have found that the optimal values of the methane pressure, the cell temperature and the cell length can be determined through a kinetic analysis. The conclusions can be valuable for designing configurations of an end-pumped DPAL.

Influence of deviation in central wavelengths of both a seed laser and a pump LD on the output features of a DPAL-MOPA system

A master oscillator power amplifier (MOPA) is thought to be a suitable equipment to realize the power scaling for a diode pumped alkali laser (DPAL). In fact, the characteristics of a DPAL-MOPA system strongly depend on the central wavelengths of both a seed laser and a pump laser due to the extremely narrow nature linewidth for atomic alkali. In this report, a theoretical model of an end-pumped DPAL-MOPA system is first developed to study the influence of deviations in central wavelengths on the output features. Then, the relationship between the environmental parameters and the output linewidth as well as the output power is analyzed. The results reveal that the deviation in central wavelengths of both a seed laser and a pump LD will lead to a dramatic decrease of the output power for a DPAL-MOPA system. The conclusions are thought to be helpful for design of an end-pumped DPAL with high powers.

Influence of excitation on physical features of a diode-pumped alkali laser

In recent years, a diode-pumped alkali laser (DPAL) has become one of the most hopeful candidates to achieve the high power performance. A series of models have been established to analyze the DPAL’s kinetic process and most of them were based on the algorithms in which only the ideal 3-level system was considered. In this paper, we developed a systematic model by taking into account the influence of excitation of neutral alkali atoms to higher levels on the physical features of a static DPAL. The procedures of heat transfer and laser kinetics were combined together in our theoretical model. By using such a theme, the continuous temperature distribution has been evaluated in the transverse section of a cesium vapor cell. The calculated results indicate that the excitation plays an important role during the lasing process, which might deepen the understanding of the kinetic mechanism of a DPAL.

Reviews of a Diode-Pumped Alkali Laser (DPAL): a potential high powered light source

Diode pumped alkali vapor lasers (DPALs) were first developed by in W. F. Krupke at the beginning of the 21th century. In the recent years, DPALs have been rapidly developed because of their high Stokes efficiency, good beam quality, compact size and near-infrared emission wavelengths. The Stokes efficiency of a DPAL can achieve a miraculous level as high as 95.3% for cesium (Cs), 98.1% for rubidium (Rb), and 99.6% for potassium (K), respectively. The thermal effect of a DPAL is theoretically smaller than that of a normal diode-pumped solid-state laser (DPSSL). Additionally, generated heat of a DPAL can be removed by circulating the gases inside a sealed system. Therefore, the thermal management would be relatively simple for realization of a high-powered DPAL. In the meantime, DPALs combine the advantages of both DPSSLs and normal gas lasers but evade the disadvantages of them. Generally, the collisionally broadened cross sections of both the D1 and the D2 lines for a DPAL are much larger than those for the most conventional solid-state, fiber and gas lasers. Thus, DPALs provide an outstanding potentiality for realization of high-powered laser systems. It has been shown that a DPAL is now becoming one of the most promising candidates for simultaneously achieving good beam quality and high output power. With a lot of marvelous merits, a DPAL becomes one of the most hopeful high-powered laser sources of next generation.

Theoretical investigation of output features of a diode-pumped rubidium vapor laser

In the recent years, diode-pumped alkali lasers (DPALs) have been paid many attentions because of their excellent performances. In fact, the characteristics of a DPAL strongly depend on the physical features of buffer gases. In this report, we selected a diode-pumped rubidium vapor laser (DPRVL), which is an important type among three common DPALs, to investigate how the characteristics of a DPRVL are affected by different conditions. The results signify that the population ratio of two excitation energy-levels are close to that corresponding to thermal equilibrium as the pressure of buffer gases and the temperature of a vapor cell become higher. It has been found that quenching of the upper levels cannot be simply ignored especially for the case of weak pump. The conclusions are thought to be helpful for the configuration design of an end-pumped DPAL.