What is a LASER? Monochromatic Light

Project Description

Part one of a three part investigation of what make LASER light different from other light. In this lesson, we will demonstrate the monochromatic nature of LASER light by comparing the spectra of white light and colored LEDs to that of LASER 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: 1 Diffraction Grating, 3 Light BLOX in Red/Green/Blue, White LED, 1 Red LASER Pointer, a blank wall/screen

Download the FREE Lesson – Monochromatic Light

Featured Products
Light Blox

Light Blox

Explore Optics OSA 100 Kit

Explore Optics OSA 100 Kit

Step 1

Get Started

Let’s investigate one of the aspects of LASER light that makes it different from “normal” light.

Hold the diffraction grating up to one eye.

Instructor Tip:

When you are done with this, move on to Parts 2 (Collimated Light)  and 3 (Coherent Light) to cover the other two properties of LASER light: Coherent and Collimated.


Step 2

Observe the spectrum of white light

Look through the diffraction grating towards the white LED. Don’t look directly at the light; rather slightly to the left or right of the source.

What do you see? Record the order of the colors, starting from closest to the light source.

Instructor Tip:
White light consists of all the colors of the rainbow – it is made up of many wavelengths of light so it is NOT monochromatic. The “rainbow” observed through the diffraction grating are the wavelengths of light that make up that white light.

Now hold the diffraction grating up to a flashlight, the overhead lights, (NEVER THE SUN).Was the rainbow the same for all sources of white light? What do you expect to see for the colored light from the Light Blox?


Step 3

Observe the spectrum of Colored Light

Repeat the process with the red, blue and green Light Blox. Do you expect to see only red light or a spectrum?

What do you see? Was this what you expected? Why/why not? What’s going on?

Instructor Tip:
This image is of the spectrum generated by a red LED. You can see that there are several wavelengths of light present. Its not the full “rainbow” you see with white light, but clearly the LED is not monochromatic (consisting of only a single wavelength)


Step 4

Observe a Laser through a diffraction grating

Point the red LASER pointer towards a blank wall or screen, approximately 15-20 cm away from the surface.

IMPORTANT: Never look directly into the LASER!

Step 5

Hold the diffraction grating about 5-10 cm from the front of the LASER, and switch on the LASER pointer so that the laser beam passes through the diffraction grating onto the wall.

What do you see? How is this different from the light from a Light Blox? What does this tell us about what makes LASER light special?If you have a green laser pointer, try it with green and see what happens.

Instructor Tip:
What you are seeing here is the diffraction pattern of monochromatic (single wavelength) red laser light. Because there is only one wavelength (RED, 635nm) you only see the beam splitting into many red dots, not a spectrum; there are no other colors (wavelengths) present. This is monochromatic, one of three properties of laser light.

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