Introduction

Abstract

In 1960, Maiman (USA) created the first source of coherent optical radiation, namely, a ruby laser emitting in the red spectral region (λ = 0.6943 μm) [1.1]. Several years later a great family of lasers was already in existence. The following types were known:

• 1) solid-state lasers, e.g., Nd:CaWO₄ laser emitting at 1.065 μm [1.2], neodymium glass laser (λ = 1.06 μm) [1.3], Nd:YAG laser (λ = 1.064 gm) [1.4]

• 2) gas lasers, e.g., He-Ne laser (λ = 0.6328, 1.1523, 3.3913 μm) [1.5], argon ion laser (λ = 0.4880, 0.5145 μm) [1.6], CO2 laser (λ = 9.6, 10.6 μm) [1.7];

• 3) dye lasers [1.8,9]

• 4) semiconductor lasers [1.10–12];

and so on. The wavelengths of the above mentioned lasers were either fixed or tunable over a small range. It was a matter of practical importance to widen the range of wavelengths generated by laser sources.