Hello everyone. 
I'm Charles Clark. 
And I'm going to conduct some lectures on 
practical use of quantum mechanics to 
solve some real physics problems. 
The very interesting type. 
These are some of the most important 
problems in the early days of quantum 
physics, which led to the understanding 
of the structure of atoms. 
In enough detail to make possible number 
of applications that are very important. 
For example the development of the laser 
and it's a subject that was not imp-, 
important not only in the early days but 
it's a very vibrant field of research 
today. 
Since 1997, about 11 Nobel prizes in 
physics have been awarded. 
For innovative use of the interaction of 
light with atoms to do things like con, 
create ultra controlled ultra cold 
matter. 
develop new optical frequency standards, 
and the like. 
So it's a very vibrant field of research. 
And I hope these lectures will give you 
some sense of the excitement. 
And ma, and an impression of how you 
could actually approach it yourself. 
Now this is a fairly field with a lot of 
material in it, and I've only time to 
give you a brief introduction. 
So, let, let me just draw to your 
attention the fact that we have a page 
accessible along the main page of the 
website, Additional Materials. 
And we've put in a selection of original 
scientific literature with commentary 
there on various aspects that are 
important. 
So the things that are going to be talked 
about in detail in the first set of 
lectures by me are the Bore model of the 
atom. 
Not necessarily in this order the 
discovery of deuterium, fascinating story 
of which there's both a detailed and a 
sort of a simplified account. 
Recommend you look at. 
the, the green laser pointer and the 
photoelectric effect. 
Well, come to think of it, and the 
Young's Double Slit experiment. 
So, there's a very, couple introductory 
paragraphs in each one of these. 
if you find something that interests you 
in the lecture, I suggest you take a 
look. 
In fact the homework will require that 
you actually, read part of Einstein's 
original paper, on the photoelectric 
effect. 
It's, it's an awesome paper. 
And you have a choice of reading it in 
the, German original, which we provide 
you, or in the English translation that 
is available we give you a link to the 
English translation. 
At Wikimedia. 
Okay, let's begin talking about the 
world. 
Here's a happy scene. 
I'm sure you've all felt like this at 
some time, you're walking along and a 
very clear day, all of a sudden you see a 
beautiful rainbow. 
Now the world is full of colors. 
And the one's first impression is that 
the sun is a sort of a pure white light. 
It's a very natural color. 
It seems to display things. 
In some optimal way for us. 
They often like to inspect an object by 
taking it out in the open sunlight and 
seeing what it looks like. 
So the original impression of humanity is 
that the sun was the source of all light. 
Indeed, you know, maybe fires would 
produce something, but for a long time 
there were no artificial lights. 
And occasionally it would show, these 
effects where you would see in the 
otherwise clear sky a spectrum that 
seemed to contain all the possible colors 
of human experience. 
Now here's another example using a fairly 
natural material, a piece of glass, where 
we see a case where a white light comes 
in and then a number of other colors, red 
blue, are emitted. 
Basically, the white light is spread, 
somehow changed into a spread out system 
of colors. 
Now, this is a phenomenon that was known 
in antiquity. 
And people then seemed to think that 
there was something about the. 
The shape of the prism or the qualities 
of the glass that impressed different 
colors on sunlight, which was otherwise a 
clear white light. 
But Newton showed that this was not the 
case, and that in fact that sunlight was 
a mixture of colors. 
And it's by one of these experiments that 
when you hear about it you think it's so 
obvious. 
What he did was, he took sunlight, and 
put it through a prism. 
But then he, he took some of the 
separated light, a light of a pure color, 
and put it into a second prism, and he 
saw there that no further separation of 
the colors occurred. 
So the natural way of interpreting that 
result, is that white light is a, is for 
some reason a mixture of all these colors 
put together. 
And what the prism does, is separate them 
out. 
we call this the dispersion of the 
colors. 
by the by the prism. 
Now, from today's stand point we know 
that color is an index of the light's 
wavelength. 
Lambda. 
Conventional designation for the 
wavelength of light. 
And, there's a famous equation, which 
you're going to get some more practice 
with. 
The relationship between frequency, Nu, 
and wavelength Lambda. 
So, Nu is equal to c over Lambda, where C 
is the speed of light. 
Oh, so C has the units of meters per 
second, or length divided by time, Lambda 
has the units of length. 
And what is a wavelength, a wavelength is 
a wave motion. 
The wave length is the distance over 
which the wave motion begins to repeat 
itself and C is the speed of light. 
So what we as you're going to see there 
is a conventional way of designating the 
characteristics of light in the optical 
region of the spectrum and I'll explain 
to you why that is. 
Now, here's a little inverse example of 
what you saw in the prism. 
A very elegant and interesting 
demonstration made by Alexander Albrecht 
of the University of New Mexico. 
This is a prize winning photograph from 
the membership magazine of the Optical 
Society of America, December 2012. 
So, what is done here is, there are these 
three three pipes of water, there's water 
streaming into a bowl and then a laser is 
put into the into the pipe and the laser 
beam is entrained in the water. 
This is a demonstration you may have seen 
before, but what's done here is a red, 
green and a violet laser are used to, put 
the light of separate colors in the bowl. 
Then the light scatters around, and so 
what you see coming out from your eye is, 
it's a, it's a scattered combination 
containing, you know, more or less the 
same quantity of red, green and violet. 
So that gives a white appearance, very 
nice. 
Now the these three lasers are of a 
common type and we're going to, they're 
all actually available as laser pointers. 
And, and, they light in this region of 
wavelengths is available as a very 
inexpensive laser pointer, costing 
between five and ten American dollars. 
And so we are going to use, throughout 
these lectures, these three lasers as 
sort of standard reference lasers, for 
the for the discussion of the course. 
So the red laser, at a wavelength of 650 
nanometers, a green laser, at a 
wavelength of 532 nanometers, this is the 
famous diode pump solid state. 
The wavelength produced by diode pump 
solid state architecture that's used in 
the green laser pointer. 
And then finally, the wavelength of four 
or five nanometers, which is the 
wavelength. 
Sorry, wavelength of the blue, using the 
blu-ray laser, so if you have a blu-ray 
system or a Playstation at home, you are 
the already the proud owner of one of 
these four or five nanometer lasers. 
Okay, and so now as an introduction to. 
The application of some of these basic 
concepts of optics. 
I mean, I'll give you a little inline 
quiz, that has to do, with the properties 
of one of my favorites, which is the the 
green laser pointer. 
Okay, I hope that some of you found that, 
example, relatively easy. 
I hope all of you found it at least 
interesting. 
The idea that you can use a passive 
crystal to change the color of light is 
something that's only become possible 
well since the development of the laser 
in the 1960's. 
And to learn a little bit more about that 
I recommend this paper on the green laser 
pointer it's written, I hope in a fairly 
accessible way it's not highly technical 
and does provide a simplified description 
of the operation device if you're 
interested. 
Now one thing that you're going to have 
to do if you want to be a successful 
physicist or a successful scientist any 
time, is to lose your sense of 
complacency. 
When you wake up everyday, you see the 
white light of the sun. 
You see the rainbow from time to time, 
you see the same colors over and over. 
You might think, what else is there? 
Well, the answer is revealed. 
By being able to look where no one has 
looked before. 
And that's really the, why we do quantum 
physics today, is to try to understand 
things at a deeper level. 
And here is an example of how that type 
of deep understanding, made on an 
observation by a man who, you know, alone 
in the world at the time, had the 
capability. 
Of making those detailed observations 
made a tremendous change in science and 
history, and that man was Joseph von 
Fraunhofer, one of the most skilled 
optical physicists of his day. 
He was a specialist in making various 
types of optical glass that had very high 
dispersion, so he could make prisms. 
That would separate out light to greater 
the different colors of light to a 
greater degree than any one else, and 
here is a paper from his publication and 
in fact that you can acquire that 
publication through our additional 
materials uh,document of course its 
written in German actually rather an old 
fashioned type of German. 
Maybe some students in the German 
discussion group can comment upon that. 
But this is a drawing produced by 
Fraunhofer of what he saw when he looked 
at the light of the sun using a highly 
dispersive prism. 
He saw dark lines in the spectrum. 
So, imbedded in this rainbow, there were 
patches of darkness. 
Hundreds of them. 
Now, well, might you ask, how did he know 
that those were patches in the light of 
the sun itself, rather than maybe 
something in the earth's air, that would 
be blocking? 
would, would be doing something in the 
sunlight. 
Well it's a good question, and Fraunhofer 
answered it, at least in part. 
By also looking at the light from other 
stars, in particular the star Sirius, is 
one that he reports. 
And he saw other dark lines there, but 
not necessarily exactly the same dark 
lines that were in the sun. 
So, in other words, at least a number of 
these dark lines are definitely 
associated with the light of the sun. 
Now, you know there's been many ideas of 
color and of the nature of the sun and 
everything throughout history. 
But I don't know of a case where 
someone's just sat down and said, well, I 
bet there's a whole bunch of dark lines 
in the light of the sun that we just 
haven't seen yet. 
And maybe someday, someone's going to 
invent some optical device that will 
allow them to be revealed. 
So now let's take another, we'll take a 
look. 
At, a more modern observation, the same 
thing. 
Behold the crown of the great king of the 
solar system, the sun. 
Here's a wonderful image, that's a 
spectrum of the sun seen at high 
resolution produced at the, the, National 
Optical Astronomical Observatory in 
Tucson, Arizona. 
And let me just describe to you how this 
was taken. 
Let's say that you're looking at the 
rainbow in the skies. 
So here's the red bow that's above and 
then down at the bottom, there's a violet 
one, and then, from violet, we go to 
blue, I guess it is. 
Then to green. 
And to yellow. 
And, and orange, and so on back up to the 
red. 
So here's a, here's a crude drawing of 
the rainbow. 
So you, if you, if you had a picture of 
that. 
And then you, cut out, a little thin 
strip like that, now you take, this thin 
strip. 
Orient it here. 
So for example this could be the red, the 
sort of, the red patch. 
And then down here this would be the 
violet. 
Then what you do is that you, you cut out 
50 of these strips, like this and then 
what you do is you stretch. 
Stretch each one of these out to expand 
the region so this enables you, in other 
words if you were to take these 50 strips 
there 50 strips stacked vertically here. 
And if you lay them end to end you would 
see the rainbow but with the resolution 
that allows you to see all this fine 
detail. 
Now for your guidance I have positioned 
some of our reference lasers near where 
they would be in this spectrum. 
Here's 650 nanometers, 532. 
The blu-ray laser. 
And now what this indicates is that, the 
wavelength is I'll, I'll draw it on this 
side. 
The wavelength is increasing within a 
strip as you go from the right to the 
left because this is short wavelength, 
and you're going backwards, you see. 
So you're, you're increasing the 
wavelength. 
And then it's also increasing as you go 
from one strip to the next. 
Is that clear? 
Well you're going to now get an 
opportunity to see whether you grasp the 
concept. 
Okay again I hope that some of you got 
the, material on the online quiz and, and 
everyone found at least. 
Interesting enough to, to think about the 
problem that's not it's not complicated. 
A heavy map but its a good experience in 
actually you know looking at the results 
of experimental data and understanding 
very clearly what that representation 
means because these things aren't always 
obvious. 
Okay, that's it for today, and I will, 
well, that's it for this lecture. 
We'll resume and talk more about 
interference, and attraction.