Pulsed laser unit producing linearly polarised light - uses optical feedback path length to determine pulse length

摘要

The length of the pulse of coherent light produced by this laser is determined by the length of time taken by a proportion of the output light to travel along an optical feedback path. The initial stimulating light input is switched into the amplifying medium (2) by a polarising switch or Pockel cell (1). 90% of the resultant light is coupled through a semi-reflecting mirror (4), while the remaining 10% is reflected by two mirrors (5,6) back to the light input (3). Between the two feedback mirrors (5,6) are a half-wavelength plate (7) and an absorbing medium (8). The length of the path is related to the pulse length by the equation t equals c/d, where C is the speed of light. Thus a path length of about 30 cm. will produce a pulse length of 1 nano-second.