| 摘要 |
1,263,628. Lasers. AMERICAN OPTICAL CORP. 24 June, 1969 [6 Nov., 1968], No. 31744/69. Heading H1C. [Also in Divisions C1 and C4] A gas laser oscillator 10, Fig. 4, is optically aligned with a laser amplifier 14 which comprises a glass fibre active medium 24, Fig. 3, having an inner cladding 22 of a lower refractive index and an outer cladding 26 of higher refractive index, the outer cladding being suitably doped to absorb strong laser radiation. The optical fibre is of sufficiently small cross-section that only the lowest order HE 11 mode is propagated. The gas laser may be helium-neon radiating at 1À0621 micron, and the glass fibre formed of a suitable neodymium-doped glass having a peak of spontaneous emission which matches the helium-neon output. A suitable glass composition in weight per cent is 61À32% SiO 2 , 11À75% Na 2 O, 2À94% K 2 O, 12À25% CaO, 7À06% TiO 2 , 0À68% Sb 2 O 3 and 4À00% Nd 2 O 3 . For absorption at this wavelength the outer cladding 26 is doped with samarium. Other suitable glasses are SiBaRb, Ba(PO 3 ) 2 , LaBBa, SiPbK, LaSiAl and GeBaRbK, the dopant being Nd<SP>3+</SP>, Er<SP>3+</SP>, Tm<SP>3+</SP> or Ho<SP>3+</SP>. The laser system shown in Fig. 4 includes an isolator in the form of a Faraday rotator or the combination of a “ wave plate and a polarizer to prevent spontaneous emission feedback between the amplifier 14 and the oscillator 10. Alternatively the ends of laser 14 may have an anti-reflection coating or have ends inclined at an angle of about 10 degrees, Fig. 5, to deflect Fresnel reflected light. A plurality of amplifiers 14, 15 may be used which are separated by an optical filter 30.
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