Optical instruments are how we see the world, from corrective eyewear to medical endoscopes to cell phone cameras to orbiting telescopes. This course will teach you how to design such optical systems with simple mathematical and graphical techniques. The first order optical system design covered in the previous course is useful for the initial design of an optical imaging system but does not predict the energy and resolution of the system. This course discusses the propagation of intensity for Gaussian beams and incoherent sources. It also introduces the mathematical background required to design an optical system with the required field of view and resolution. You will also learn how to analyze these characteristics of your optical system using an industry-standard design tool, OpticStudio by Zemax.
Radiometry units
Loading...
来自 University of Colorado Boulder 的课程
Optical Efficiency and Resolution
个评分
从本节课中
Radiometry
One of the main questions you ask when designing an optical system is "How much light can I get through the system?" In this last section of new content for this course, we move from talking about resolution to talking about the amount of light we expect at each point in the optical system, a field of study called radiometry.
与讲师见面
Amy SullivanResearch Associate
Electrical, Computer and Energy Engineering
Robert McLeodProfessor
Electrical, Computer and Energy Engineering
To understand radiometry, we need just a couple of things.
And the first is a good set of units and jargon.
And without that, you're really in trouble.
So let's get those first.
We're going to talk about the total amount of optical
flux that we get through our system.
This is in watts or joules per second.
I don't know if this is good jargon or bad, but
the symbol that's traditionally used for power, thi, is the same symbol we use for
optical power of a lens describing whatever its focal length.
And I could've used the different sample here, but thi
is the standard in the literature, so I'm giving you with the unit you'll run into.
So just have to keep track of the fact that we mean different things by power
in different cases here.
Also problematic is that everyone, or
most everyone, is a bit sloppy on the word intensity.
And I've used this already in this class to mean watts per area, power per area.
However, formally in the discipline of radiometry,
intensity is a different thing.
And intensity is of a point source, and it's the total power radiated
into a solid angle described in steradians, that's what sr is there.
So when we're being careful and
doing radiometry we have to be formal with the language.
That intensity is a quantity of point sources, power per solid angle,
not of areas.
The thing which describes the power in an area
is irradiance with a symbol E, that's watts per unit area.
So formally we should say whenever we talk about
how much light is falling on an area we should say irradiance.
It's extremely common in optics to be a little sloppy and
to instead use the more English or common jargon word of intensity.
Throughout this radiometry section, I will be careful and I will use these quantities
correctly, and I'll try to always mention the units to remind you.
So yeah.
Total power watts.
Watts per unit solid angle intensity, watts per area irradiance,
and probably most important quantity of all is the combination,
watts per solid angle per area.
And that may not make sense yet, but one of the primary goal of this module is to
make you understand the radiance concept and how incredibly fundamental it is.
These are sort of a scientific units to describe radiometry as
we have coined this power in watts and joules for energy.
There's a parallel set of units that describe how things appear to the human
eye and the difference there is that our eye has a spectral response curve and
it's most sensitive in the green.
So a certain number of watts isn't
actually way to describe how illuminated the appears to the eye.
You have to care about the spectrum.
So it's a parallel set of units that are all like these
that have that spectral response built in.
And they don't add anything, that the physics is fully
captured by these more scientific sets and units so I'm just going to use them.
However, you should know that this concept of radiance, which is so
important in the photometric units, the ones that know about they eyeballs
specter response curve, their radiance is called brightness.
And again this concept of radiance is so important that another sloppiness you will
hear is that people will use the word brightness interchangeably with radiance.
We will hear about the constant radiance theorem here fairly quickly.
And you will hear it referred to and
I have done it myself as the constant brightness theorem.
It's not wrong they are both the same quantity fundamentally,
one simply has a spectral response built in.
But just again jargon,
you may hear people use radiance and brightness somewhat interchangeably.
And they have roughly the same units, but there's an extra integration
in the photometric units to deal with the eyeballs' response.
Okay. Language.
Now let's start putting some math on things.
You may not be used to dealing with solid angles.
I'll review that here in a minute.
But fundamentally, a solid angle, I'll give you a little cartoon here,
is defined as, if you took a portion of a sphere,
the area of the cap of that cone divided by the radius of the sphere.
And that describes a solid angle, because notice by analogy here,
regular angle theta would be the length of an arc over the radius of the arc.
So it's just the analogy from one dimensions now to two dimensions.
And we're going to be radiating light to the two dimensions a lot.
So we're going to need that.
So if we had a point source who remember who would be describe by
this intensity quantity, we would take the total power in watts.
And divide by some cone that were gathering up from that point source.
And we describe that cone to its solid angle.
So there is the definition of intensity.
Conversely, if we were looking at a surface of plane,
either light going on to a plane or coming off and
there's a formerly, a slightly different jargon there, but,
for our purposes it doesn't really matter which direction the lights going.
So, for planes we talked about the total optical power,
in watts, divided by the area of the plane we're looking at.
And then, finally, radiance must be the combination of those.
If we're looking at a plane,
it turns out that each point in that plane can be thought of as a little point.
And therefore it radiates into some solid angle, but
then we might also be interested in how much of the plane we're looking at,
capital A and so that's where this quantity radiance shows up.
Real sources radiate both into angle and have finite area and
hopefully that's beginning to immediately ring a bell about the shape of light, and
that it's described by two rays.
Or in the case of Gaussian beams, well two rays as well.
That the combination of area and angle is related and you need both quantities.
And this is just the beginnings of how we're going to take these units and
start using them.
So, for example, if you
stop this video right now and find a piece of paper and
you tilt the piece of paper to look at how the light
that appears to come off that paper changes as you foreshorten the paper.
As you see more and more of the unit area on the paper,
but in a projection it'll look smaller to you by the cosine theta.
And the question is does the paper appear to be brighter and
does the paper as you tilt it to be 90 degrees.
So now the entire piece of paper is collapsed to an infinitesimally small
point.
Do you blow the universe up or do you blind yourself because the light is so
incredibly bright?
I think you will find you don't.
But this argument would kind of suggest you do because you're for
shortening that paper and seeing all of it in a smaller and smaller area.
These are the kinds of questions we are going to figure out in this module.
