X, K and KA bands are specific, different radar frequencies used on various radar guns. Lazer (laser or lidar) is police laser. POP band is a very quick, short pulse of radar, meant to avoid being detected by cheap radar detectors. As a previous poster mentioned, cheap radar detectors are not good at detecting POP band. Additionally, no radar detector is protection against police laser.
Contrary to a previous post, MANY people use sophisticated radar detection and laser jamming equipment and NEVER get speeding tickets. He may be pointing and pulling the trigger, but we have already slowed down because WE KNOW WHERE HE IS! But, I guess it's nice to keep them fooled. ;-)
If you can't afford at least $200 for a radar/laser detector, just slow down. You'll save yourself money from buying a useless radar detector, and potentially insurance points, time off of work, court costs and fines when your cheap radar detector fails to detect a hidden speed trap. To address the previous poster's concerns: the best radar detectors also detect POP and instant-on radar, as well as police laser (LiDAR).
But, if you are concerned about police laser, you'll need a laser jammer. You can't detect laser unless it is aimed at your vehicle. The laser only has to hit your vehicle for 0.2 seconds to read your speed; not nearly enough time to adjust your speed if your laser alarm alerts. A laser jammer jams the laser gun's speed reading while alerting to the laser, giving you time to check your speed before turning off the jammer. Like radar detectors, laser jammers are LEGAL to use in almost every state.