Why is the the first order useful?

  • Thread starter Choisai
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In summary: AOMs work.In summary, the conversation discusses the use of diffraction in AOLM and Digital Micromirror Devices, and the question of why the first order of diffraction is used instead of the zeroth order. The first order is preferred because it has more power, while the zeroth order is not modulated and therefore does not show the desired signal. This is due to the acoustic modulator used in AOLM, which changes the refractive index and creates a grating effect. The zeroth order does not experience this change in refractive index, making it less useful for the desired signal. The same principle applies to Digital Micromirror Devices, which use tiny micromirrors instead of
  • #1
Choisai
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I've been looking into diffraction for AOLM and stuff like that, and these produce diffraction. Binary Spatial Light Modulators like Digital Micromirror Devices also produce diffraction. This diffraction is then focused and filtered using a pinhole. But, and here is the question:

Why is always the first order of diffraction used and not the zeroth order?

The first order has more power than the 2nd, 3rd or other higher orders. That's something I get. But why is the zeroth order of diffraction not used? I've been seeing on several websites that the zeroth order is not 'modulated', but why isn't it? Isn't the zeroth order just as valid to use as the 1st? I have added an image of a 4f system and you can see it discards the zeroth order. Why?

EDIT: AOLM stands for Acoustic Optical Light Modulator (more commonly known as just AOM) and adds the frequency of soundwaves to light. For an example, if you want to add several MHz to light (of several THz) you can do so using an AOLM.
 

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  • #2
Do you really expect us to know what AOLM means? You got to be kidding. Even without really knowing what you mean, it's clear that the zeroth order is no good because it is not modulated. That means the signal you're looking for won't show up in the zeroth order fringe.
 
  • #3
I get the zeroth order is not modulated, but why is the zeroth order not modulated?

PS: I added an explanation of what an AOLM is to my question
 
  • #4
Choisai said:
I get the zeroth order is not modulated, but why is the zeroth order not modulated?

PS: I added an explanation of what an AOLM is to my question

Ask yourself this question: what is the AOM doing to the lens? How does this change with frequency?
 
  • #5
It uses sound wave to change the refractive index. This index-modulation creates relatively more opaque and less opaque area, which acts like a grating. The zeroth order is made up of light coming through this grating, but I guess that isn't the part that gets refracted by the change in index? And therefore the zeroth order is the unmodulated order?

If these assumptions of mine are correct, how do they extend to more general applications, such Digital Micromirror Devices that use pinhole filtering? There is no change in refractive index when you use a DMD, only tiny micromirrors (usually 10 micron in size).
 

Related to Why is the the first order useful?

1. Why is the first order useful?

The first order is useful because it allows us to understand and predict the behavior of a system or phenomenon. It is the simplest type of differential equation and provides a foundation for more complex mathematical modeling.

2. What are the applications of the first order?

The first order is used in various fields such as physics, engineering, economics, and biology. It is used to model physical systems, analyze growth and decay processes, and understand the dynamics of chemical reactions.

3. How do we solve first order equations?

First order equations can be solved using various techniques such as separation of variables, integrating factors, and substitution. These methods help us find the general solution to the equation, which can then be used to solve specific problems.

4. What are the limitations of first order equations?

First order equations have limited applicability as they can only model simple systems. They also assume a linear relationship between variables and do not account for factors such as friction or external forces. In some cases, higher order equations may be needed to accurately model a system.

5. Why is it important to understand first order equations?

Understanding first order equations is crucial in many scientific and engineering fields as it helps us make predictions and design solutions to real-world problems. It also provides a stepping stone for more advanced mathematical concepts and modeling techniques.

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