The script is not explicit on their purpose :
INT. THEED - POWER GENERATOR ELECRIC BEAM - HALLWAY
The SITH LORD, followed by QUI-GON, enters a long hallway filled with a
series of deadly rays that go on and off in a pulsing pattern that shoots
down the corridor every minute or so. DARTH MAUL makes it down several walls
of deadly rays before they close. QUI-GON is one wall away from the DARK
LORD. OBI-WAN is just starting into it and is five walls way from DARTH
But, according to the Wookieepedia Qui-Gon Jinn article, it's a security system.
While his Padawan rushed to catch up, Jinn and Maul moved on, passing through an impenetrable laser shield security system to one of the cooling pits.
I finally found a well buried article on Wookieepedia: Laser gate. It also explain the reason why they are cycling on and off.
Laser gates, also known as electron walls, were designed to protect high-security or dangerous areas by sealing them off with a wall of energy. Laser gates were installed in the Theed Generator Complex on Naboo. The barriers were strong enough to easily block a lightsaber strike and would vaporize any matter that touched them. These gates were crucial to the death of Qui-Gon Jinn at the hands of Darth Maul as the laser gates prevented Jinn's Padawan, Obi-Wan Kenobi, from coming to his aid against the Sith. However, the generators were unable to keep up the immense energy needed to power the gates, and so they would cycle on and off approximately every five minutes. Each gate remained open for only around ten seconds before cycling on again.