X-Message-Number: 13934 From: Date: Tue, 13 Jun 2000 15:16:30 EDT Subject: Shock pumped laser for QND biological reader Back on line for some weeks, I add some technical informations about the laser system used in a Quantum NonDemolition brain (or more broadly, biological organ) reader. Energy source for the chemical laser. I have said before that the chemical laser, the first element in the three stage laser train, will be shock pumped metal vapor desing. I have pointed out the analogy between the shock generator and a very big rocket motor in the 32 000 tons thrust range. Here I must explain briefly how a rocket motor works: Some propergols are burned in a combustion chamber at high pressure and subsonic speed. At the chamber exit, the presure drops by a factor near 1.8 and the flow become both, sonic and turbulent. This is the throat nozzle domain. Beyond that, the bell shape of the nozzle allows a rapid expansion then near the nozzle exit the flow is redirected in the motor axis to get the most useful thrust. The first expansion generates a depressurisation shock and then the near exit redirection produces a compression shock. Rocket designers try to play with shapes and local sonic velocity so that both shocks forms at the same place and cancel each other. If they fall, to do that, there is first a decompression shock and then a reconpression shock nearby down the gas flow. In a laser the objective is to get an inverted "bad rocket" with fist a commpression shock to pump atoms in an excited state and then decompression zone where the asing action takes place. Such nozzles are first conical, then near cylindrical on a short distance to form the compression shock and then comes the fan out section requested to form the deconpression shock. No surprise, this is very bad for thrust, indeed if we want to extract gas energy in a laser process, it can't be recovered in the mechanical form of a thrust. Another desing starts from a classical bell nozzle and cut the redirection section. A device in inserted in the gas flow just beyond the nozzle throat so that a compression shock is formed here. By varying the position, shape and diameter of the obstructing body many configuration can be tested. This is attractive for 3 reasons: - Simple multiple testings in different conditions may overcome a weak hydrodynamical computation capability. - The compression shock forms at higher pressure and this is best for laser pumping. - The lasing domain is smaller and so needs smaller mirrors and optical systems. Yvan Bozzonetti. Rate This Message: http://www.cryonet.org/cgi-bin/rate.cgi?msg=13934