Power and lasing threshold for longitudinally pumped lasers with intracavity raman self-conversion

Abstract

A method is developed for calculating the power and lasing threshold for longitudinally pumped lasers with intracavity Raman conversion. The theoretical analysis is based on equations for the powers of light beams in the cavity. Expressions for the power and lasing threshold of a Raman laser with self-conversion as functions of the parameters of the active medium, cavity, and pumping, taking into account the overlap of all the interacting beams, are derived and analyzed.Keywords: Raman conversion, Raman laser, light beam, spatial overlap of light beams, power and lasing threshold.Introduction. Many applications (spectroscopy, biology, medicine, etc.) require laser light at wavelengths not covered by conventional lasers. Coherent radiation in these bands is widely obtained by means of nonlinear-optical frequency converters, prominent among which are the ones based on induced Raman scattering, including Raman converters with a scattering medium in the cavity (Raman lasers). The cavity usually provides a substantial enhancement in the efficiency of Raman conversion and, of special importance, makes it possible to obtain cw radiation at the required frequency using low power cw lasers as pump sources [1][2][3][4][5][6][7][8][9].There are two types of Raman lasers. In the first, a scattering medium is placed in a high-Q cavity and external radiation, most often introduced through one of the cavity mirrors, is used for pumping (Raman laser with external pumping) [1][2][3][4]7]. In the second type, a scattering medium is placed in the cavity of a laser whose radiation also undergoes Raman conversion within the cavity (Raman laser with intracavity pumping) [5,6,[8][9][10][11][12][13]. The advantages of this type include a high intensity of the primary laser radiation inside the cavity (at the frequency of this radiation the cavity can be almost completely closed) and the fact that it is not necessary to match the spatial structure and frequency of this radiation to the mode structure of the cavity. For large spectral widths of the laser transition of the active medium of the primary laser (substantially higher than the intermode frequency beating) and for the vibrational transition on which the Raman scattering takes place, this matching takes place automatically.Raman conversion with intracavity pumping is extremely practical and convenient for creating small sized, fully solid state cw Raman lasers, including lasers with Raman self-conversion, i.e., lasers in which generation of the primary radiation and its conversion into a Stokes beam take place in one and the same medium. High efficiency diode lasers can be used to pump this type of laser, although they yield broad band, low quality laser beams, so that they are poorly suited for direct Raman conversion.In this paper we present a theory of lasers with Raman self-conversion and pumping along the cavity axis (at the end of the active medium). A number of experimental studies of such lasers are currently known [5,[9][10][11][12], but as far as we know there is no deta...

Stationary generation of diode-pumped self-Raman Nd:YVO4/YVO4 composite crystal laser

“…The equations obtained previously [10] form the basis for discussing the above experimental results. It is noteworthy that the conditions for applying them were fulfilled in the experiment.…”

“…This was 12% of the diode pumping power. The equations obtained previously [10] and estimates of the focal lengths of thermal lenses induced in the composite crystal by transformations of the pumping radiation into the primary laser radiation and this radiation into the Stokes component were used to analyze the experimental results. It was shown that thermal effects play a very important role in forming the spatial structure and diffraction losses of the beams in a cavity with plane mirrors.…”

“…If the transverse distributions of light-beam intensities are modeled as co-axial Gaussian functions, then these parameters are defined by the equations [10]:…”

“…The theory indicates {Eq. (18) [10]} that the power of the laser radiation exiting the cavity through mirror M 2 during generation of the Stokes component is determined by…”

“…The experimental results were discussed using previously published equations [10]. Focal distances of thermal lenses induced in the crystal by generation of the primary laser radiation (pumping lens) and its Raman-transformation into the Stokes component (Stokes lens) were estimated.…”