​Laser characteristics of sapphire crystal (2)

Laser characteristics of sapphire crystal (2)

Among Al2O3-based laser media, the most common ones are Cr:Al2O3 and Ti:Al2O3. The application fields of these materials are discussed in Chapter 1.

Cr: Al2O3. Ruby as an active medium has the following advantages [94,95]: high pulse energy; possibility of cao operation at room temperature; highest mechanical strength compared to other laser media; good radiation from pump light sources high limit of surface and bulk damage under the influence of self-radiation. The characteristics of ruby as a laser medium are listed in Table 1.11.

Ruby can effectively absorb the emission of pump light sources in the blue and green regions of the spectrum. The laser emission of ruby can be recorded by a low-inertia vacuum photon receiver. In the radiation region of the ruby element, this photon receiver has high sensitivity and stability. In one aspect, the ruby laser can be compared with the more efficient laser illumination at the threshold position of the object. At the same time, the threshold value of ruby excitation and generation is four levels higher than that of the active medium.

Optical strength. Surface damage (chips or cracks) and bulk damage (stars or trails) of sapphire may occur immediately after laser exposure. The threshold for surface damage is determined by surface quality and is often lower than the threshold for bulk damage Micro-cracks in the surface layer and even edges and corners can focus laser radiation. Another source of damage is radiation absorption by abrasive particles present in adjacent layers of the surface.

For short pulses, the threshold damage energy is inversely proportional to the radiation duration, tp. For long pulses, the damage threshold is not determined by tp. The location of the transition region is determined by the surface structure. For quasi-amorphous and crystalline surfaces, the dependent behavior is at tp = 5•10-6 s and tp = 2•10-6 s. The layer adjacent to the surface absorbs ~10% of the laser pulse energy. In a 1 μm thick layer, when the radiation energy density is 0.5 GW/cm3 and tp=30 ns There is a pressure of ~200 N/m2, resulting in a "micro-explosion".

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