Temporally modulated laser with an alkali vapor amplifier.

A diode-pumped alkali laser has gained rapid development in recent years. In this study, we take the advantages of high-gain cross section and low upper energy lifetime of an alkali laser to propose, to the best of our knowledge, a novel type of time-domain-modulated alkali vapor amplifier. By using the amplifier, we experimentally demonstrate the power scaling of a modulated seed laser. The study should offer a new methodology to construct a practice high-power and high-modulated laser source for long-distance light detection and ranging systems in the future.

Dual-wavelength end-pumped Rb-Cs vapor lasers.

Diode-pumped alkali vapor lasers (DPALs) have been rapidly developed because of their excellent performances. However, there have been few reports about DPALs with multiple wavelengths until now. The effects of the output features on the waist size and position of both Rb and Cs pump beams were first theoretically investigated using a kinetic model for an end-pumped dual-wavelength Rb-Cs laser. Then, a continuous-wave (CW) laser was experimentally constructed. Finally, the hybrid CW-modulated output with two wavelengths was also successfully obtained for the first time in development of alkali lasers. The results might be helpful in applications for laser communication and ranging/radar in the future.

Theoretical analyses of an injection-locked diode-pumped rubidium vapor laser.

Diode-pumped alkali lasers (DPALs) have drawn much attention since they were proposed in 2001. The narrow-linewidth DPAL can be potentially applied in the fields of coherent communication, laser radar, and atomic spectroscopy. In this study, we propose a novel protocol to narrow the width of one kind of DPAL, diode-pumped rubidium vapor laser (DPRVL), by use of an injection locking technique. A kinetic model is first set up for an injection-locked DPRVL with the end-pumped configuration. The laser tunable duration is also analyzed for a continuous wave (CW) injection-locked DPRVL system. Then, the influences of the pump power, power of a master laser, and reflectance of an output coupler on the output performance are theoretically analyzed. The study should be useful for design of a narrow-linewidth DPAL with the relatively high output.

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.

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 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 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.

Algorithm for evaluation of temperature distribution of a vapor cell in a diode-pumped alkali laser system (part II).

With high efficiency and small thermally-induced effects in the near-infrared wavelength region, a diode-pumped alkali laser (DPAL) is regarded as combining the major advantages of solid-state lasers and gas-state lasers and obviating their main disadvantages at the same time. Studying the temperature distribution in the cross-section of an alkali-vapor cell is critical to realize high-powered DPAL systems for both static and flowing states. In this report, a theoretical algorithm has been built to investigate the features of a flowing-gas DPAL system by uniting procedures in kinetics, heat transfer, and fluid dynamic together. The thermal features and output characteristics have been simultaneously obtained for different gas velocities. The results have demonstrated the great potential of DPALs in the extremely high-powered laser operation.

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.

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.