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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 2mmdiameter 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 Qswitch 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 '" [OWCarbon 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 Lowcarbon steel of Srmn thickness is to be cut with a laser at a speed of
1.25 mlmin with a 0.5mm 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 SwiftHook and Gick. estimate the power required to produce a weld of
2mm width and 4.5mm 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 4ltW 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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 Spring '10
 Chapmann

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