e894a4g - ENSC460I894 Assignmet 4 Nov 20 2003 due Nov 27...

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Unformatted text preview: ENSC460I894 Assignmet 4 Nov. 20, 2003 due Nov. 27 2003 1 Assuming that the diffraction spreading (divergence) of a HeNe laser beam (It = 0:6328 um) can be approximated by assuming it is equivalent to the diffraction caused by a plane monochromatic wave incident on a circuiar aperture of diameter equal to the laser beam diameter. calculate the diver- gence for a 2-mm-diameter beam. 2'. Calculate the refractive index difference per cenumeter in lithium niobate (LiNbOg) for an applied field of 1090 Wem. How long must a longitudinal Pockels cell be to cause a phase change of 90‘ between the fast and slow rays for ruby laser light (it = 0.6943 gm)? 3 What angle should a KeNe laser beam make relative to the normal, to the surface of an acousto—optical modulator operated at 40 MHz with an acoust- ical wavelength of 60 pm? What is the shift in frequency of the optical wave, assuming the optical wave has a propagation component in the same direction as the acoustical wave? ,4A solid laser consists of mirrors separated by 50 cm with a laser rod 10 cm in length with a refractive index of 1.5 and a Q-switch with a length of 2.5 cm and a refractive index of 1.45. What is the frequency spacing between axial modes for this laser? 5(a) 51:38:30 11131:: galance approach. estimate the power required to pro . e mm in diameter a d - “"1" a 1'5 pulse from a C0; laser. 11 I mm deep '" [OW-Carbon steel p -- 7.86 g/cm’. d= 0.07 cmzls C = 0.7 Jig K, k = 0.4 chm K Estimated values near the melting point are T... = 1809 K L; = 13.8 lemol 6 Low-carbon steel of S-rmn thickness is to be cut with a laser at a speed of 1.25 mlmin with a 0.5-mm kerf. Using energy balance. estimate the power that must be coupled into the material. it = 0.4 chm K p = 7.36 g/cm’ C = 0.50 Jig K L” = 350 kilmol L, = 13.8 kJImol r. = 3135 K 1 7 Mild steel is to be welded with a multikilowatt C0; laser. Using the model of Swift-Hook and Gick. estimate the power required to produce a weld of 2-mm width and 4.5-mm depth at l rm'min. 0<= 0.09 sing/s k = 0.4 chm K Tm = 1309 K using a pulsed Nd—YAG laser with a 4-ltW peak power output. Use energy balance to estimate the energy needed and the pulse length. assuming a nearly 9 - 8.9 Wm’ square pulse. Show that the time to reach vaporization at the surface is neg- L 298 ”I t I lizible. based on the results of the uniform irradiance model. ° . I i “ ' i i o - ‘- 8 Hales are to be dnl e l! - "If,“ C d Cl 3 I d 0 5 lb ck n Rel Will] a lame! 0f 0.] mm! C 3; 0.44 I}; K L.-63031!g r. - 1736K r,- aims. ‘R 9;” ...
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