This is the final 'proper' chamber for this chapter and it's - naturally - one of the slightly more complex ones. Once you're done with this, we'll be on to the ninth and final chapter!
Before you even enter the chamber properly, the path ahead of you will collapse, so use the Conversion gel to cross the gap.
Now reinstate the beam, hit the plunger once again and now use the gel to bounce yourself up into the beam. With the gel behind you, jump out of the beam once you're safely over the chasm and stand on the red switch to reverse the beam's direction of travel.
Keep standing on this switch until the gel has passed through both portals (and is heading towards the transportation beam device itself). Make a quick mental note of the three turrets behind the glass to your right along with the square light wall panel up and to their left.
Once the gel is around 3/4 over the turrets heads, cancel the beam and the gel will fall down, taking out all three turrets, allowing you to safely hit the button at the other side of the glass. Hitting this button will reveal a slanted wall panel near the entrance to the room.