Q11S. An Er:YAG laser beam of spot size A =5mm2impinges on tissue. Let assume th

Question

Q11S. An Er:YAG laser beam of spot size A =5mm2impinges on tissue. Let assume the tissue is mostly holding water. The absorption coefficient for this lase is =15000cm1, how long Would it take vaporize a disk of tissue of thickness L=1/ if the laser is pulsed with a period T= 1ms power is P =5W?

0.17s

1.7x10-5s

1.7x10-3s

1.7s

None of the above  

Q12s- An Er:YAG laser beam of spot size A= 5mm2impinges on tissue .Let assume the tissue is mostly holding water. The absorption coefficient for this lase is =15000cm2, how long Would it take vaporize a disk of tissue of thickness L=1/ if the laser is pulsed with a period T= 1ms? Assume the power is 5W for 0.25 ms andis 0W for 0.75ms within the period T. Not:You may use results from Question 11S if the work

6.75 ms

0.17 s

6.75x 10-5s

6.75 s

none of the above

Q13s- Calculate the relaxation time for the pulsed aslaser as described in question 12using K=103cm2/s and a = 1500 cm-1

A.16.7ms

B.16.7s

C.1.1s

D.1.1ms

E.none of the above

Q14- Based on data given in questions 12S and 13s, which of the following statement is correct?

A). During a period, cycle, the laser is on for more than 200 and it is not off for long enough to allow heat to diffuse. Thermal damage will occur because there is not enough time for the Heat to diffuse

B. During a period cycle, the laser is on for about 67 and it is not off for long enough to allow heat to diffuse. Thermal will occur because there is not enough time for heat to diffuse

C). During a period, cycle, the laser is on for more than. 200 and it is off for long enough to allow heat to diffuse. Thermal damage should not occur as there is enough time for heat to diffuse

D). during a period, cycle, the laser is on for about 67 and it is off for long enough time for heat to diffuse. Thermal damage should not occur, as there is enough time for heat to diffuse

E.) no thermal damage would result as the laser is running

Q15s- A power density of 50 W/cm2 can be absorbed by the rods and the cones found in the retina beyond this power density, thermal damage occurring in the retina a dye laser is tuned at    = 47 1nm and is impinging on the cornea then focused on the retina. The focusing system of the eye has a focal length of about it; find the power density on the cornea of the eye. W0 near the eye is 1 mm and the laser is 5 mW

A. 1.59 x10-3 W/cm2

B. 1.59 W/cm2

C. 159 W/cm2

D.0.159 W/cm2

E. none of the above

Explanation / Answer

Q15s)

(D)0.159 W/m^2 is the correct answer.

I = 5 mW = 5 x 10^-3 W

We know tat I = P/A

I = 5 x 10^-3 W / 3.14 x (0.001)^2 = 159 W/m^2

I = 159 W/m^2 = 0.159 W/cm^2

Hence, (D)0.159 W/m^2 is the correct answer

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