Polymer passive laser switches were made from new polymethine dyes in a polyurethane matrix. They were designed for passive mode locking in neodymium lasers emitting 1.05-1.08 um radiation. The service life of a local working zone of such a switch was found to be 10 6 pulses with an energy of 4 -6 mJ in a train. Pulse-periodic passive mode locking was achieved at frequencies 50 -100 Hz. Replacement of polyurethane acrylate composites, formed by radical polymerisation, with polyurethane matrices, formed by the polycondensation method, increased by more than one order of magnitude the main operating characteristics of the lasers.Solid-state lasers emitting ultrashort pulses are used extensively in studies of fast processes, which require high peak powers [1]. Generation of ultrashort pulses is simplest in the case of passive mode locking when saturable absorbers based on organic dyes are used [1]. Such absorbers should be highly efficient and photostable, they should have short excitedstate relaxation times, large absorption cross sections a, a reasonable service life, and be easy to use [1,2]. The last requirement is fully satisfied by solid-state passive laser switches (PLSs), particularly those with polymer matrices which are coloured by organic dyes [3][4][5][6][7][8]. Replacement of liquid PLSs with solid switches increases the reproducibility of the temporal and energy parameters of the output radiation [5,7] and simplifies greatly laser design. Passive switches [4,5] which are free films without facilities for mechanical displacement of the working zone are unsuitable for pulse-periodic lasers and have to be handled carefully because of their low resistance to abrasion. It is much preferable to adopt a triplex block configuration [3,6,7] in which a coloured polymer film is sandwiched between optical substrates that ensure the removal of heat, prevent penetration of atmospheric oxygen, and protect the polymer film from mechanical damage.We investigated the operating characteristics of our new PLSs based on a polyurethane matrix coloured with polymethine dyes and intended for the emission range A las = 1.05 -