SOLAR PUMPED LASERS TO DIRECTLY CONVERT SOLAR RADIATION TO LASER RADIATION
G. Gaviraghi, P. Marzocca, J. Miller, Sh. Payziyev, C. Radley*, A. Sinclair, K. Taggart,
*Corresponding Author, firstname.lastname@example.org, Leeward Space Foundation,
216 Maple St, Americus, GA 31719, 831-425-2807, http://www.LeewardSpaceFoundation.org
It has been proposed to use microwaves to beam down power to Earth from space based solar power stations in Geosynchronous Orbit. However the Rayleigh diffraction limited optics requires enormous antennas, typically a few kilometers in diameter, and huge power levels, of 5GW to 10GW. A much lower cost of entry investment (100x lower) is afforded by use of optical or infrared lasers with much shorter wavelength, hence much smaller system size, e.g. 10MW, with one meter size collimator mirror diameter. Since there is no "grid power" in space, most spacecraft today use solar power sources, mostly photovoltaic solar cells. Powering lasers requires high levels of power. PV solar cells are usually less than 25% efficient. This multiplied by a typical 20% “wall plug” efficiency of lasers results in overall a mere 5% efficiency (95% waste heat!). This strongly motivates interest in solar pumping of lasers to greatly increase overall efficiency. Theoretical efficiency of about 38% is possible. Other potential benefits of solar pumped lasers would be reduced weight and reduced number of components affording higher reliability (reduced number of failure modes) versus an electrically pumped laser powered from PV cells.
Space based solar power beaming would be most cheaply and efficiently performed using lasers with solar pumping, versus PV electrical pumping. High power and high efficient solar pumped lasers have a large potential for other applications, e.g. nano-materials production, materials processing, magnesium cycle of hydrogen production, free space laser communications, energy transmission. There recently was reported high-efficiency lasing (40% efficient, 300 mW) by using an advanced ceramic, Cr:Nd:YAG ceramic laser medium, and an artificial solar-light pumping source. This material lases at 1064 nanometres wavelength. This has opened up ample opportunities for creation of highly effective solar pumped lasers with wide range of powers, on the basis of different solar concentrators or Fresnel lenses, which in turn can promote occurrence of new environment-friendly laser technologies.
We propose the development of a pilot line of solar laser based laser research, development and use of high-effective solar pumped lasers taking advantages of the highly-sensitized Cr:Nd:YAG ceramic laser mediums and the thin-disk laser technologies. To reach this challenging target, project partners will develop new high-efficient lasers, will research in parallel the most suitable architectures of solar lasers and cost-effective solar laser technologies, and will demonstrate space power beaming technology with solar powered lasers.
Solar lasers have been researched for 50 years with major emphasis on free space wireless optical communication and power transmission applications. Realization is now within reach with advanced ceramic laser materials. The innovation is the development of solar pumped lasers by combining advantages of the highly-sensitized Cr:Nd:YAG ceramic laser mediums (other than above mentioned active element of a rod-form with a low concentration of Cr3+ ions) and the thin-disk laser technologies.
If the efficiency of the laser pumped by solar light is 20%, in order to provide 200kW laser power there will be a need for 1MW of solar power which can be harvested from ~1250m2 at solar radiation intensity at the Earth surface ~800W/m2. In principle this can be realized with the lasers on large scale solar concentrators like the Uzbek big solar furnace (BSF), but from the practical point of view and also in order to meet the requirements such as low cost of equipment and quick return, it is preferable to build the laser-power station consisting of fiber bundle coupled lasers on small-scale parabolic concentrators. For instance a single laser module can be implemented on parabolic concentrator with a diameter of 1-2m. In the case of 2m concentrator the solar power collected will be of about 2.5kW from which 500W laser power can be obtained at efficiency of 20%. So, in order to reach the power of 200kW there would be a need for 400 such laser modules.
Nanotechnology has made it possible to achieve high transparency, large-size, homogeneous solid state laser materials. The ceramic fabrication technology was a fundamental breakthrough for the development of high-power laser applications. In particular, the wide opportunity has emerged for creation of the powerful and highly efficient solar pumped lasers. Recently, it was reported high-efficiency lasing (38% efficient) by using an advanced ceramic, Cr:Nd:YAG ceramic laser medium, and a metal halide lamp as an artificial solar-light pumping source. However, the laser output was only 300mW level.
Combining advantages of the highly-sensitized Cr:Nd:YAG ceramic laser mediums (other than above mentioned active element of a rod-form with a low concentration of Cr3+ ions) and the thin-disk laser technologies could allow to reach high efficiency, close to the result obtained with artificial solar light at the laboratory conditions. This will be a major technology breakthrough.
The principle investigator of this project will be Dr. Shermakhamat Payziyev. He designed and fabricated the stand of the solar laser on the base of the Big Solar Furnace (BSF) at the Institute for Materials science of the Scientific and Production Association “Physics-Sun” (Uzbekistan). Using crystalline Nd3+:YAG rods his team demonstrated the possibility of utilization of 1 MW BSF for pumping purposes. Laser radiation power of 80W has been obtained from single Nd3+:YAG rod with working sizes of 6x130 mm installed in the multi-element secondary concentrator.
Another main result of these studies was the development of a computer model of the solar lasers which is based on ray-tracing and Monte-Carlo methods. The model makes calculations for lasers of a various configuration and active elements of the different form. Based upon experimental results and with use of the computer models there have been performed numerous calculations for different laser configurations. It was shown that the conversion efficiency of solar energy into the laser can be up to 25% of the solar flux energy collected at the focal area of BSF.
We propose to develop new high-efficient lasers, and to research in parallel the most suitable architectures of solar lasers and cost-effective solar laser technologies. Dr. Payziyev will relocate to Clarkson University in New York, USA where the research will be performed, under Leeward Space Foundation Research Fellowship.
This fund is being raised by Leeward Space Foundation (LSF), which is a 501c3 tax exempt non-profit corporation in Georgia, USA. Donations to LSF may be tax deductible to certain US taxpayers, e.g. individuals who itemize deductions.
This article in the Economist explains the huge benefits of solar pumped lasers for solving the energy crisis and climate change:
Magnesium power -White-hot energy
New power sources could be made using magnesium
Apr 19th 2010