Unit 11 Problems

CC2404 Applied Physics and Instrumentation in Health Care Problems Unit 11 (2009) 1.

(a) State three characteristics of laser which make the laser different from the conventional light. (b) Explain photocoagulation in laser treatment. (c) What is the intensity required for the process photo-vaporization? (d) State two conditions for the photo-vaporization. (e)What is the difference between photo-vaporization and photochemical ablation?

2.

What is the energy difference in eV between the excited energy state and ground state of a ruby laser with wavelength 694 nm? 3.

Compute the intensities of an argon laser of wavelength 512 nm: (a)

photocoagulation of the retina using 500 µ m diameter spot and laser power of 200 milliwatts (mW), (b) photo-vaporization of opacities within eye using 50 µ m diameter spots and laser power settings of 2 Watts (W). (c) Calculate the number of photons emitted per second in (b). (d) Calculate the laser fluence in (b) for an exposure time of 5 s. 4.

A KrF excimer laser operates in pulse mode, with energy of 300milliJoules (mJ)

per pulse and the pulse rate is 5 Hz. Each pulse lasts for 1 nanosecond (ns). The laser beam is focused on a spot of diameter 1 mm. (a) Calculate the instantaneous power output during each pulse. (b) What is the average power of the laser?