What is a Laser? Part 3: Coherent Light

Project Description

This is part three of a three part investigation of what makes LASER light different from other light. Part 1: Monochromatic Light and Part 2: Collimated Light.

In this part, we’ll demonstrate that LASER light is coherent by comparing the interference pattern of a red LASER pointer to that of an LED light.

Grades: 9 to 14
Duration: 1/2 Hour – 1 Hour

NGSS HS-PS4-5 Communicate technical information about how some technological devices use the principles of wave behavior and wave interactions with matter to transmit and capture information and energy.

Supplies: Set of Light BLOX in Red/Green/Blue, 1 Red LASER Pointer, a blank sheet of paper

Download the FREE Lesson – Coherent Laser Light

Featured Products
Light Blox

Light Blox

Explore Optics OSA 100 Kit

Explore Optics OSA 100 Kit

Step 1

Watch this video.

Step 2

This activity will explore an aspect of LASER light that contributes to its amazing quality.

Switch on the Light Blox and hold it close to the paper, at a small angle. The light should stretch out in front of the Light Blox. Take a close look at the light. What do you observe? Is there anything unusual about the light?

Step 3

Now, hold the LASER pointer the same way, and switch it on. The LASER light should form a long ellipse.

What do you observe about the LASER light? Is there anything unusual happening? How is it different from the light from the Lazr finger?

You might have to move between the Light Blox and the LASER pointer a couple of times before you see the difference in the light – keep going until you see it!

Now that you know what the speckle pattern looks like, move the LASER slowly while shining it on the paper. What do you observe about the speckle pattern? Why do you think this happens?

Step 4

See how many other coarse surfaces you can find to observe the speckle pattern on. The skin on the inside of your elbow is a good one.

Does the speckle pattern change? How so?

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