Miniature Laser Systems Research Articles

Thermo-Optic Numerical Research on Segmented Circular LD Arrays Side-Pumping a Nd:YAG Laser Rod

The configuration designs of the laser diode (LD) side-pumping laser rods focus on how to solve the space conflict between the pump and heat-removal devices because both want to use the larger lateral surface of the laser rod. The conflict is better balanced in the three different side-pumping geometries: the segmented circular LD array side-pumping configuration, the annular liquid-cooling structure, and the compensated semicircular LD array side-pumping arrangement. The temperature distributions and thermo-optic effects of the laser rod in the segmented circular LD array side-pumping configuration are analyzed in contrast with those in the other arrangements. The numerical results indicate that the periodical segment-pumping scheme provides higher beam quality than the compensated semicircular side-pumping scheme, enabling removal of the complex liquid cooling system in medium-power applications, thus showing the potential to be used in compact and miniature laser systems.

Ultranarrow Linewidth Photonic‐Atomic Laser

AbstractLasers with high spectral purity can enable a diverse application space, including precision spectroscopy, coherent high‐speed communications, physical sensing, and manipulation of quantum systems. Already, meticulous design and construction of bench Fabry–Perot cavities has made possible dramatic achievements in active laser‐linewidth reduction, predominantly for optical‐atomic clocks. Yet, there is increasing demand for miniaturized laser systems operating with high performance in ambient environments. Here, a compact and robust photonic‐atomic laser comprising a 2.5 centimeter long, 20 000 finesse, monolithic Fabry–Perot cavity integrated with a micromachined rubidium vapor cell is presented. By leveraging the short‐time frequency stability of the cavity and the long‐time frequency stability of atoms, an ultranarrow‐linewidth laser that enables integration for extended measurements is realized. Specifically, the laser supports a fractional‐frequency stability of at an averaging time of 20 millisecond, at 300 second, an integrated linewidth of 25 Hz that results from thermal noise, frequency noise floor as low as 0.06 Hz2 Hz−1, and a passive vibration immunity as low as 10−10 g−1. The present work explores hybrid laser systems with monolithic photonic and atomic packages based on physical design.

Random lasing from dyed polystyrene spheres in disordered environments

Advance designs of random lasers toward the development of miniature laser systems are in demand. Random lasing from Rhodamine-B dye doped polystyrene microparticles was demonstrated. Bare polystyrene spheres were used as scatterers, and these provided optical feedback to the gain. Random lasing was successfully demonstrated in two different disordered environments: in binary colloidal solution and in photonic glass. Incoherent feedback occurred in both the cases, and laser emission was obtained with a spectral line width of ∼10 nm. Optimized number densities of bare and dye doped polystyrene microparticles required for random lasing action in such systems were evaluated. Although both disordered media showed random lasing with similar number densities of the microparticles, the lasing threshold in the case of photonic glass was lower in comparison to binary colloidal solution. This was because of higher index contrast and larger filling fraction of microparticles in the case of photonic glass. Lasing results obtained for photonic glass were compared with their previous results of Bloch lasing in photonic crystal synthesized using similar dye doped polystyrene microparticles.

Miniaturized Lab System for Future Cold Atom Experiments in Microgravity

We present the technical realization of a compact system for performing experiments with cold $^{87}{\text{Rb}}$ and $^{39}{\text{K}}$ atoms in microgravity in the future. The whole system fits into a capsule to be used in the drop tower Bremen. One of the advantages of a microgravity environment is long time evolution of atomic clouds which yields higher sensitivities in atom interferometer measurements. We give a full description of the system containing an experimental chamber with ultra-high vacuum conditions, miniaturized laser systems, a high-power thulium-doped fiber laser, the electronics and the power management. In a two-stage magneto-optical trap atoms should be cooled to the low $\mu$K regime. The thulium-doped fiber laser will create an optical dipole trap which will allow further cooling to sub-$\mu$K temperatures. The presented system fulfills the demanding requirements on size and power management for cold atom experiments on a microgravity platform, especially with respect to the use of an optical dipole trap. A first test in microgravity, including the creation of a cold Rb ensemble, shows the functionality of the system.

Laser Spark Ignition in lean burn CNG Engine

The CNG Engines play a dominant role in transportation and energy production. The CNG engine is an environment-friendly engine, which causes drastic reduction in emission to the environment by using CNG as a fuel in IC engine. Spark plugs work by sending small; high-voltage electrical sparks across a gap between two metal electrodes Spark plugs can ignite leaner fuel mixtures, but only by increasing spark energy. Unfortunately spark plug cannot ignite leaner air-fuel mixture for long time it produce exhaust emission as well as reduce the efficiency of engine. ON the other hand, Laser ignition system of engines represents a more and more realistic alternative to traditional spark plug or high-frequency ignition approaches. Its ability to ignite extremely lean mixtures of fuel and air allows one to efficiently reduce the NOX concentrations in the exhaust gases, which are associated with potential long-lived ignition components. In this project, an overview of the laser parameters necessary to ignite the most common lean burn air-fuel mixtures for CNG engines is presented. Furthermore, a novel approach for multipoint laser ignition is discussed as a viable path for speeding up the long combustion durations of lean mixtures. Finally, an innovative approach to compact, robust, and relatively cheap laser ignition is described, which involves miniature laser systems. The passively Q-switched laser head is ideally mounted on each cylinder, while the optical pump should be located far away. Ignition energies in the range of slightly more than 1mj per pulse are realized with the involvement of perfect optical focusing.

Segment side-pumped Q-switched Nd:YAG laser

In the design of conduction-cooled lasers, a side-pumped configuration is an attempt to solve the space conflict between pump and heat removal. The pump radiation always competes with the heat removal and mechanical support device for the lateral surface of a laser rod. This space conflict can be addressed by a segment side-pumped configuration in which circular laser diode arrays and heat-conducting rod holders alternate periodically along the length of the laser rod. This scheme permitted 11 Hz operation of a 190 mJ Q-switched laser at the wavelength of 1064 nm without the use of liquid cooling for both the laser rod and laser diode arrays and the corresponding optical-optical conversion efficiency of 23.1%. Thus, it has great potential to be used in compact and miniature laser systems.

Self-optimizing approach for automated laser resonator alignment

Nowadays, the assembly of laser systems is dominated by manual operations, involving elaborate alignment by means of adjustable mountings. From a competition perspective, the most challenging problem in laser source manufacturing is price pressure, a result of cost competition exerted mainly from Asia. From an economical point of view, an automated assembly of laser systems defines a better approach to produce more reliable units at lower cost. However, the step from today's manual solutions towards an automated assembly requires parallel developments regarding product design, automation equipment and assembly processes. This paper introduces briefly the idea of self-optimizing technical systems as a new approach towards highly flexible automation. Technically, the work focuses on the precision assembly of laser resonators, which is one of the final and most crucial assembly steps in terms of beam quality and laser power. The paper presents a new design approach for miniaturized laser systems and new automation concepts for a robot-based precision assembly, as well as passive and active alignment methods, which are based on a self-optimizing approach. Very promising results have already been achieved, considerably reducing the duration and complexity of the laser resonator assembly. These results as well as future development perspectives are discussed.

Segmented circular LD arrays side-pumped a Nd:YAG laser rod

We design a Nd:YAG module with symmetrical LD side-pumped structure in a periodical arrangement between circular LD arrays and holders. This novel design has great potential to be used in compact and miniature laser systems. Design optimization and simulation on thermal effects have been performed. An experiment has also been carried out. The experiment results indicate the all-solid-state laser with the-Nd:YAG module can stably operate in the range of 10–30 Hz with no controlling temperature by TE cooler. The laser beam had a divergence angle less than 3.8 mrad and a maximum output pulse of 174 mJ has been obtained at the pump current of 50 A and working frequency of 23 Hz, corresponding to optical-optical conversion efficiency of 40.2%.