Properties of Laser Light: Monochromatic
This science lesson is part one of a three part investigation of what makes LASER light – or the Properties of 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. The other two lessons explore the Collimated and Coherent nature of Laser Light.
Grades: 9 to 14
Duration: 1/2 Hour – 1 Hour
NGSS Connections PS4.B: Electromagnetic Radiation
- 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 (HS-PS4-5)
Get Started with the properties of laser light
Let’s investigate one of the Properties of LASER light that makes it different from “normal” light.
Hold the diffraction grating up to one eye.
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.
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?
Observe the Spectra 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?
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)
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!
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 the properties of laser light are?If you have a green laser pointer, try it with green and see what happens.
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.