Start by creating a new blank image or open the image you wish to add the burnt-in text to. If you’d like to just do a simple version of the technique without an image to apply it to, just fill the background layer with whatever solid color you like (preferably not an extremely dark color though).
Select the Type tool and choose the the Type Mask tool from the Options bar at the top of your screen (or click and hold on the Type icon and drag to the right). Next click inside the image and type your text. Click the check mark in the Options bar to finalize the text layer (or click OK if you’re using an older version of Photoshop).
You should now see a selection of your text. Move it to the location on the image where you want it to be burned into the surface.
Click on the New Layer icon on the Layers Palette to add a new layer, and make sure that the new layer is the currently selected layer. Choose the color you want to use for the burnt-in text (the example uses black). Choose Edit » Fill to fill the selection with your foreground color by pressing Option+Delete (PC: Alt+Delete).
Without deselecting the text, click on the layer that contains your main image (i.e. the background layer). Using the keyboard’s arrow keys, move the text’s selection one (1) pixel down and one (1) pixel to the right.
Choose Image » Adjustments » Brightness/Contrast, and move the Brightness Slider to about 75% (you may want to choose a higher or lower setting depending on how dark the surface of the image you’re burning into is). Click OK.
Again, using the arrow keys, move the selection two (2) pixels up and two (2) pixels to the left.
Choose Image » Adjustments » Brightness/Contrast, and move the Brightness Slider to -75% (negative 75). Again, you may want to choose a higher or lower setting depending on the situation. Click OK.
Press Cmd+D (PC: Ctrl+D) to deselect and see your finished work.