Week 5 case study
Laser energy and power
Introduction
Lasers are common technology used in a wide range of applications. A laser pulse is composed of a packet of photons all with a similar wavelength and frequency traveling at the speed of light. The energy of each photon in the laser pulse is given by the following formula:
where h = 6.63×10-34 J*s (called Planck’s Constant)
In this case study, you will employ this formula, the speed of light, and the concept of power to determine the properties of a specific laser. To get started, review the following example:
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Example
A laser is used in eye surgery. The laser wavelength is 514.5 nm and it’s Pulse Power is Ppulse = 1.5 Watts in each laser pulse. During the surgery the laser is pulsed for a time duration of 50 ms
During that pulse how many photons are produced?
The laser wavelength is given. We want to find the frequency first
.
The energy of each photon.
=
The Energy of the pulse is defined by the product of the pulse power and the time so
Then the energy of each pulse is ,075 Joules. The number photons n is:
17 is the number of photons produced in this pulse.
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Exercise
Now that you’ve reviewed the example above, it is time to explore the properties of a different laser. Review the case below and answer the questions that follow. Please show all your work below for full credit.
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A surgical laser with a wavelength of 810 nm delivers 250 mW of power on the retina of a patient. It produces a 1.5 msec duration pulse of light.
1. What is the energy of each photon? (30%)
2. What is the laser energy per pulse? (30%)
3. How many photons does it produce? (30%)
4. In what region of the spectrum is this light? (10%)
