Thrust measurements and evaluation of asymmetric infrared laser resonators for space propulsion

Since modern propulsion systems are insufficient for large-scale space exploration, a breakthrough in propulsion physics is required. Amongst different concepts, the EMDrive is a proposed device claiming to be more efficient in converting energy into propulsive forces than classical photon momentum exchange. It is based on a microwave resonator inside a tapered cavity. Recently, Taylor suggested using a laser instead of microwaves to boost thrust by many orders of magnitude due to the higher quality factor of optical resonators. His analysis was based on the theory of quantised inertia by McCulloch, who predicted that an asymmetry in mass surrounding the device and/or geometry is responsible for EMDrive-like forces. We put this concept to the test in a number of different configurations using various asymmetrical laser resonators, reflective cavities of different materials and size as well as fiber-optic loops, which were symmetrically and asymmetrically shaped. A dedicated high precision thrust balance was developed to test all these concepts with a sensitivity better than pure photon thrust, which is the force equivalent to the radiation pressure of a laser for the same power that is used to operate each individual devices. In summary, all devices showed no net thrust within our resolution at the Nanonewton range, meaning that any anomalous thrust must be below state-of-the-art propellantless propulsion. This puts strong limits on all proposed theories like quantised inertia by at least 4 orders of magnitude for the laboratory-scale geometries and power levels used with worst case assumptions for the theoretical predictions.

The Endless Corridor

How old is the image of a mirror reflected in a mirror reflected in a mirror, etcetera? Is it of relatively recent vintage, or is it an ancient idea? What name can we even apply to it? Does the idea have any practical uses, or is it only a curiosity? Certainly it shows up in such devices as Fabry-Perot interferometers, plano-plano laser resonators, and interference filters. We can trace references of it back through time, and show where it might have been known, if not recorded. It can confidently be traced back to the beginning of the nineteenth century, but evidence from the plays suggest that the image may have been known to Shakespeare.

Methods for adjusting feedback in terahertz lasers

The optimal feedback coefficient in an active open resonator is an important condition for high lasing efficiency. For precise selection of the optimum communication and maintaining the optimum in all modes of laser operation, the ability to adjust smoothly the communication is required. Terahertz (THz) lasers have a number of features that one should take into account when choosing feedback control schemes. The paper presents a review and comparative analysis of the schemes of laser resonators (THz) in the range with a smoothly controlled radiation output. The authors consider both long known and widely used, as well as the latest schemes of laser resonators. Smooth adjustment can be realized in resonators formed by metal mirrors of total internal reflection and output mirrors in the form of metal mirrors with holes or one-dimensional metal gratings. The analysis of the advantages and disadvantages of each of the considered optical schemes of laser resonators is carried out. It is shown that the given resonator schemes make it possible to control and optimize the feedback in the laser during its operation. All of them are not very complex and can be realized by re-equipping existing lasers. The choice of a specific scheme should be made in accordance with the specifics of the laser application. The use of resonators with smooth coupling control makes it possible to achieve high efficiency of lasers at all energy operating modes.