The diode-pumped alkali laser (DPAL) is a new type of high-powered laser sources which has been paid much attention in recent years. The fluorescent spectra can be used to investigate how the collisions between atomic rubidium and various buffer gases are affected when a sealed rubidium vapor cell is pumped by a LD. In this study, the cross sections between the fine-structure levels of atomic rubidium in a vapor cell were first theoretically deduced by using a gas kinetic procedure. And then, the sensitized fluorescence was experimentally obtained by means of a series of spectral measurements. Finally, the influence of the temperature on the cross section between the fine -structure levels of atomic rubidium was studied with the systematical analyses. The results are thought to be helpful for deeply understanding the theoretical characteristics of a DPAL at the atomic physics level.
It is believable that a diode pumped alkali laser (DPAL) will generate a continue-wave (CW) high-powered output in the near future. In this paper, we report the first experimental demonstration of modulating a laser-pumped rubidium-cesium vapor laser system with two wavelengths. Being different from the conventional dual-wavelength solid-state lasers in which stimulated emissions with two wavelengths often interfere with each other, the rubidium-cesium vapor laser with two wavelengths, i.e. 794.736 nm for rubidium and 894.335 nm for cesium, has a prominent advantage of employing different alkali metal vapors as laser media in the same oscillator without any disturbance in the lasing processes for dual wavelengths. In the study, we also modulated one pump source and kept the other pump source unchanged in time domain. The experimental results reveal that such a rubidium-cesium vapor laser may provide a new light source for the applications in the fields of laser ranging, laser radar, and laser surface depiction.
In the recent years, lasers around 1.6 μm are attracted much attention since their wavelengths fit the atmospheric transmission window and can be used for applications in a range of fields including laser radar, gas sensing, and free-space communications. As one of the lasing wavelengths of an Er:YAG medium is just located in the 1.6 μm region, such a laser has been gaining more and more extensive applications in the near infrared. Until now, rare literatures have been found in the MOPA (Master Oscillator Power Amplifier) study of a 1.617 μm Er:YAG laser because the effect of upconversion will become greater while a higher doping concentration is adopted. In this study, we theoretically analyze the amplification features of a 1.617 μm Er:YAG seed laser by using a multiple MOPA configuration. In the simulation, a kinetic model is established to investigate how the doping concentration, crystal length, and pump power affect the amplification efficiency of a seed laser. The results would be helpful to construct a feasible 1.617 μm laser system.
A diode-pumped alkali laser (DPAL) has been regarded as one of the most potential candidates to achieve high power performances of next generation. In this paper, we investigate the physical properties of a rubidium cell side-pumped by a Laser-Diode-Array (LDA) in this study. As the saturated concentration of a gain medium inside a vapor cell is extremely sensitive to the temperature, the populations of every energy-level of the atomic alkali are strongly relying on the vapor temperature. Thus, the absorption characteristics of a DPAL are mainly dominated by the temperature distribution. In this paper, the temperature, absorption, and lasing distributions in the cross-section of a rubidium cell side-pumped by a LDA are obtained by means of a complicated mathematic procedure. Based on the original end-pumped mode we constructed before, a novel one-direction side-pumped theoretical mode has been established to explore the distribution properties in the transverse section of a rubidium vapor cell by combining the procedures of heat transfer and laser kinetics together. It has been thought the results might be helpful for design of a side-pumped configuration in a high-powered DPAL.
In this paper, we build a theoretical model to study a continues-wave (CW) Ho3+:BaY2F8 laser by considering both energy transfer up-conversion (ETU) and cross relaxation (CR) processes. The influences of the pump power, reflectance of an output coupler (OC), and crystal length on the output features are systematically analyzed for an end-pumped configuration, respectively. We also investigate how the processes of ETU and CR in the energy-level system affect the output of a Ho3+:BaY2F8 laser by use of the kinetic evaluation. The simulation results show that the optical-to-optical efficiency can be promoted by adjusting the parameters such as the reflectance of an output coupler, crystal length, and pump power. It has been theoretically demonstrated that the threshold of a Ho3+:BaY2F8 laser is very high for the lasing operation in a CW mode.
In this study, we analyze the characteristics of a micro-cavity laser with the size one-order larger than the lasing wavelength by employing the finite-difference time-domain (FDTD) methodology. The simulation results have been obtained under the conditions with different materials and structures of the oscillator. It is seen that the power leakage from the side wall depends on the material and structure of a micro-cavity laser system. The wall material of the micro-cavity is assumed to be BK7 glass, silver, and copper, respectively. The results indicate that the side power leakage with the wall material of BK7 glass is much more serious than those with the wall materials of silver and copper. In addition, it is demonstrated that the cavity structure is also a key factor that influences the output features of such a laser.
In this paper, we introduce a new model to analyze the absorption efficiency of the laser medium for a diode side-pumped alkali laser (DSPAL). In the model, a ray trace method is employed to analyze the pump laser propagating route inside a diffusing chamber. In addition, the method, which is used to determine the total absorbed power of an alkali vapor cell, is named as the infinite convergence approach (ICA) while the random reflection is assumed to take place at the inner surface of a ceramic reflector. By considering the increase of a slit size will give rise to both increase of the input power and decrease of the reflection of the ceramic wall, we deduce that there must be an optimum slit width corresponding to the maximum absorption efficiency.
As two main atomic alkalis, rubidium (Rb) and cesium (Cs) have the similar energy-level structures. The energy transfer caused by collisions between rubidium and cesium atoms is a crucial factor for a vapor system. When such a vapor is irradiated with one component of rubidium resonance doublet, energy transfer will be induced by inelastic collisions between the excited rubidium atoms and the unexcited rubidium atoms, and between the excited rubidium atoms and the unexcited cesium atoms as well. It is noteworthy that the energy transfer between atomic rubidium and cesium is performed as cross relaxation. In this study, we theoretically investigate the effects of cross relaxations between the upper-state levels of atomic rubidium and cesium on the population distribution of the gas media. It has been demonstrated that the intensity of cross relaxations in this system is too weak to greatly affect the population distributions of atomic rubidium and cesium under the different temperatures. The conclusion might be helpful to better understand the physical features of alkalis.
Although the concept of the mode filling factor (also named as “mode-matching efficiency”) has been well discussed decades before, the concept of so-called overlap coefficient is often confused by the laser technicians because there are several different formulae for various engineering purposes. Furthermore, the LD-pumped configurations have become the mainstream of solid-state lasers since their compact size, high optical-to-optical efficiency, low heat generation, etc. As the beam quality of LDs are usually very unsatisfactory, it is necessary to investigate how the mode filling factor of a laser system is affected by a high-powered LD pump source. In this paper, theoretical analyses of an end-pumped laser are carried out based on the normalized overlap coefficient formalism. The study provides a convenient tool to describe the intrinsically complex issue of mode interaction corresponding to a laser and an end-pumped source. The mode filling factor has been studied for many cases in which the pump mode and the laser mode have been considered together in the calculation based on analyses of the rate equations. The results should be applied for analyses of any other types of lasers with the similar optical geometry.
A diode-pumped alkali laser (DPAL) is one of the most promising candidates of the next-generation high-powered laser sources. Until now, a single-heater structure has been widely adopted to control the temperature of an alkali vapor cell in plenty of the DPAL studies. However, for an end-pumped DPAL using a single heater, most pump power can be absorbed by the gain media near the entrance window of a cell due to the large absorption cross section of atomic alkali. As a result, the temperature in the pumping area around the inputted window will be much higher than those in the other positions of the vapor cell. Such a large temperature gradient would bring about some negative influences on the output performance of a DPAL. Additionally, in the worst case, the inputted cell window may even be damaged, especially when the pump intensity becomes very high. To solve the problem, we put forward a new scheme by using a gradient heating process in which several heaters are simultaneously utilized to anneal an alkali vapor cell. In this technique, the temperature at the entrance window is set to be lower than that of the other side. Using this novel method, one can not only achieve a homogeneous absorption of pump energy along the cell axis, but also decrease the possibility of the window damage in the DPAL configuration. The theoretical simulation of the laser output features by use of multiple heaters has been carried out, and the optimum condition in temperature gradient is also discussed in this paper.
A highly feasible full-field phase-measuring methodology has been developed to investigate the phase distortions of a probe beam transmitting through a LiB3O5 (LBO) crystal under different conditions. The results show that wavefront phase exhibits inhomogeneous distribution when the crystal is heated and the phase difference becomes small as time goes by when the heating temperature is kept unchanged. The technique provides an easy and feasible way to accurately measure the phase images of a probe beam transmitting through a crystal. The procedure provided in this report can be also used to study the rapid phase changes that take place in other types of optical materials.
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.
In the recent years, alkali vapor lasers have become the most promising candidates for realization of a light source with both good beam quality and high output power because of their excellent performances. A rubidium laser is a typical kind of alkali vapor lasers. In this study, we developed a theoretical mode to evaluate the population densities of three levels as well as mode-matching efficiency of a rubidium laser pumped by a narrow-linewidth Ti:Sapphire laser under two different focal conditions. In the evaluation, at least two values of the output power of a rubidium laser must be known, which are usually obtained from the experiment. We performed a series of experiments by using two pump lenses with two focal lengths of 150 and 200 mm, and acquired two corresponding values of the laser output power. Then, we applied the experimental results in the theoretical calculation and then obtained the population densities of three levels and mode-matching efficiency of the rubidium laser. The study demonstrates that the outputted pump power can be used for evaluation of the population densities of three levels and mode-matching efficiency of an alkali laser under the different experimental conditions. The study might be valuable to better understand the physical features of an alkali vapor laser and to optimize the configuration of a high-powered alkali laser in the future.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.