Step 1
Open a new 200 X 100 Image as seen below.

Step 2
Next use the gradient tool to create this look.  Make sure to hit Shift D to set your default black and white color pattern.  Drag the gradient from top to bottom of the image.

Step 3
Go to menu Filter > Render > Difference Clouds.

Step 4
Go to menu Image > Adjust > Invert or (Ctrl + I)

Step 5
Your image should look something similar to this.  If it does not you may wish to use the control F key to get a different effect.

Step 6
Go to menu Image > Adjust > Levels or (Ctrl + L) Make your levels similar to what I have below.

Step 7
Now adjust the Image > Adjust > Color Balance. Make it similar to what I have below or play around a little.
Your final product should look like this.