How Lasers Work

Laser speed guns transmit short bursts of invisible light which bounce off a target vehicle and return to the laser gun. By timing the outgoing and return trips of the light bursts, it can compute the target's speed. The laser's biggest selling point is its narrow beam--only about three feet wide at 1,000 feet--a feature that provides nearly foolproof target identification. (In comparison, a radar's beam is about 250 feet wide at 1,000 feet.)

This target-specific capability is why lasers are the tool of choice on multi-lane, heavily-traveled roadways. In the presence of dozens of targets, radar is frequently helpless, merely displaying the speed of the strongest or, on some models, both the strongest and fastest targets. But it's up to the officer to determine which vehicles are producing these speeds. In dense traffic it's a waste of time.

But a laser can easily shoot past a clump of traffic and single out a high-roller, making it nigh impossible to hide among slower vehicles.

Laser Ally during a recent test easily targeted our Expedition at 2,000 feet using only a headlight as point of aim. A radar gun would have locked-on to the much closer white pickup truck instead.

Laser guns must be used from a stationary position and are most effective at short range, usually targeting traffic at 700 feet or less.

Since laser guns use a specific light frequency, it is possible to detect a laser's signature light pulses. Keep in mind that laser detection is very different than microwave radar detection.

Since the narrow laser beam generates very little scatter--random bits of electromagnetic energy bouncing down the road--it is much tougher to detect than a radar gun that blankets the countryside with its powerful, easily detectable microwave beam.

Laser guns operate exclusively in instant-on mode, not transmitting until the trigger is squeezed. For this reason a detector usually will offer little advance warning. Similar to instant-on radar, if you're the target there will be little time to slow down. Your best hope is to use a laser detector with high sensitivity and a good field of view--the crucial ability to sniff out off-angle laser beams. So equipped, there's a small chance for advance warning of a laser working traffic up ahead

While in theory laser detectors can spot a laser beam coming from behind, we've found that a direct hit must be scored on the radar/laser detector for an alert to sound. At that point you can forget about spiking the brakes; you're toast.

That's the bad news. The good news: Laser jamming is easily done and legal in most states as well. The best laser jammers we've tested are more than a match for the latest laser guns.

Looking for something else? Go directly to: Laser countermeasures that work Action Video: How Radar Works How to get the most from your radar detector Avoid tickets: What every driver should know about police radar and lasers

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