Lateral displacement of the mode axis in a misaligned Porro prism resonator.
The lateral shift of the mode axis in a misaligned Porro prism resonator is analyzed. A method to find the tilted mode axis in a misaligned Porro prism resonator is introduced. Expressions for the displacement of the mode axis are deduced. They predict that the lateral displacement of the mode axis is proportional to the horizontal misalignment angle beta and highly dependent of the prism azimuth angle theta. Experimental results obtained agree well with theory.
Development of a high-energy Q-switched slab laser for targeting designation
A high-energy electro-optically Q-switched Nd:YAG laser at 1064 nm is presented, which can provide the largest output pulse energy of 196 mJ with the pulse duration of 12 ns and the repetition rate up to 30 Hz. The crossed-Porro resonator and zigzag slab gain medium are utilized to increase the misalignment tolerance of resonator up to 2 arcmin and minimize the divergence angle of laser beam to 1.7 mrad. We control the initial population inversion by intra-cavity quasi-CW lasing to limit maximum output pulse energy, and the excess pump energy is used to overcome performance degradation dependence on environmental temperature. As a result, a nearly constant output pulse energy can be obtained over a wide operating temperature range.
Time and Heritage
As a historian studying what can be considered a form of intellectual history, I have slowly come to adopt Michel de Certeau’s observation made at the end of the 1980s that ‘objectifying the past, for the last three centuries, has undoubtedly left unconsidered time within a discipline that has continued to use it as a taxonomic instrument’. To a certain degree, time has become commonplace for the historian who has preserved or instrumentalized it. It is not considered because it is inconceivable, but because we do not think of it or, more simply, we do not think about it. As a historian attempting to pay attention to the time I’m living in, I have thus, like many others, noticed the swift development of the category of the present until it has become obvious that the present is omnipresent. This is what I refer to here as ‘presentism’.