Open a new window, in my case its, 400 X 400. My background is white. Go to Modify> Canvas >Canvas color. Change it into white.
Import a picture of your choice to be filled in the text. Resize the picture to the canvas size.
Then select both the text and image, Go to Modify and click Mask option then select Group as Mask effect where you can see the Image is filled in side the Text like the below image.
Give a Glow effect for the Text using Glow Effect Properties.
Then select Modify and make a flatten effect of the Image.