It does more damage, and it's invincible, so no hp increase.
Before its cd got reduced (was it 40s? I don't remember) it did something like:
lvl 1: 189-234
lvl 2: 204-247
lvl 3: 220-265
lvl 4: 269-319
lvl 5: ???-??? Didn't get there
Now it does like 89-106 at lvl 1.
Note 1: All damage values were recorded at Practice Field.
Note 2: If the enemy is near, the beam can get hit him 3 times. The extra hit does more damage (looks like 30% more at lvl 1, and no, its not combo bonus, cause it's the first hit)