The 1064 nm light is fed through a bulk KDP crystal. In high-quality diode lasers the crystal is coated on the output side with an infrared filter to prevent leakage of intense 1064 nm or 808 nm infrared light into the beam.
The purpose of using a bulk KDP crystal and an infrared filter in a high-quality diode laser is to ensure that only the desired 1064 nm light reaches the target, while preventing any unwanted infrared light from leaking into the beam.