激光原理(英文).ppt

1、Laser basics,Optics, Eugene Hecht, Chpt. 13; Optical resonator tutorial: ,Laser oscillation,Laser is oscillator Like servo with positive feedback Greater than unity gain,Ruby laser example,Laser turn-on and gain saturation,Laser gain and losses,Gain decreases as output power increases Saturation,Fab

2、ry-Perot cavity for feedback,High reflectivity mirrors Low loss per round trip Must remember resonance conditions round trip path is multiple of l,High reflectivity Fabry-Perot cavity Boundary conditions field is zero on mirrors Multiple wavelengths possible agrees with resonance conditions,Laser lo

3、ngitudinal modes,Classical mechanics analog,Multi-mode laser,Fabry-Perot boundary conditions,Multiple resonant frequencies,Single longitudinal mode lasers,Insert etalon into cavity Use low reflectivity etalon low loss,Laser transverse modes,Wave equation looks like harmonic oscillator Ex: E = E e -i

4、wt Separate out z dependence Solutions for x and y are Hermite polynomials,Frequencies of transverse modes,Transverse laser modes,Single transverse mode lasers,Put aperture in laser Create loss for higher order modes,Multi-longitudinal Multi-transverse&long. Single mode,Gaussian beams,Zero order mod

5、e is Gaussian Intensity profile: beam waist: w0 confocal parameter: z far from waist divergence angle,Gaussian propagation,Power distribution in Gaussian,Intensity distribution: Experimentally to measure full width at half maximum (FWHM) diameter Relation is dFWHM = w 2 ln2 1.4 w Define average intensity Iavg = 4 P / (p d2FWHM) Overestimates peak: I0 = Iavg/1.4,Resonator options,Best known - planar, concentric, confocal Confocal unique mirror alignment not critical posit