From the Depths Wiki
Frequency Doubler
Health 100
Armour Class 4
Structural No
Weight 20
Relative Buoyancy +17.9
Size 1x1x1
Material Cost 250

The laser frequency doubler crystal can be placed anywhere in the line of the laser cavity. It increases the frequency of the laser and as such increases the armour piercing value. Multiple doublers can be added into the same cavity.
~ In-game description

A Frequency Doubler is a component of lasers that increases AP. Needed to deal full damage to most blocks, and helps with preserving damage through smoke and anti-laser shields.