January 2005
January 2005
January 12, 2005:
Read the course syllabus, and look at the course concepts map.
In the text, read the Preface, page xii, and Units and Notations, page xv. Note the existance of the useful List of Symbols, pages xvii - xxii
Read Chapter 1, focusing on Sections 1.1 - 1.5, and 1.8 - 1.10. Section 1.9 summarizes much of Section 1.7, so go back there for more information on topics that are unclear.
Problems for class discussion:
List all the properties of lasers that you find interesting or unique.List all the methods —legal or illegal— you can think of to determine the height of a tall building using a laser, without turning on the laser.
According to H. G. Wells' novel The War of the Worlds (1898), the first laser device to be operated on Earth was brought here by Martian invaders over a century ago (see page 74 of the text):
"In some way they [the Martians] are able to generate an intense heat in a chamber of practically absolute nonconductivity....This intense heat they project in a parallel beam against any object they choose, by means of a polished parabolic mirror of unknown composition .... However it is done, it is certain that a beam of heat is the essence of the matter. What is combustible flashes into flame at its touch, lead runs like water, it softens iron, cracks and melts glass, and when it falls upon water, that explodes into steam." (Chapter 6).
Is this reasonable? Assume a 10 Joule, 100 nsec, carbon dioxide laser pulse (wavelength 10 micrometers) is focused onto a metallic surface and totally absorbed in a volume 20 micrometers in diameter by 10 nm deep. Neglecting surface losses and heat conduction into the material, what will be the initial rate of rise of the temperature in the absorbing volume? Note that modern CO2 lasers can operate continuously at powers of several KW! Plus, the atmosphere of Mars is primarily CO2, and natural laser action occurs in it.
Related question: How many Joules of energy are contained in a jelly donut?
