No, an invisible infrared beam reflecting off of dust or water vapor is still invisible infrared light.
It would not have to be night time, modern NVG is quite adaptable. It would also be trivial to deliver something using the same tech as primative NVGs or basic FLIR as a countermeasure.
Dust isn’t required with IR, the whole beam will be very visible on NVG.
Where are you getting “2 seconds” from as the time necessary to kill someone with this laser?
> It can fire more than 1,000 “shots”, each lasting no more than two seconds.
The implication being not that you have two seconds to kill someone but that you have two seconds to follow the beam from its destination to its origin.
Why would particulate matter in the air not be required? There's plenty of video on youtube of IR laser pointer operation through night vision. It works the same as a visible laser.
Given you have IR laser detecting equipment suitable for daytime use (I'm not convinced your could adapt existing night vision equipment to the task) that would still require you to be expecting a laser attack to deploy it.
Come to think of it, it's not a given that the weapon even uses a wavelength visible to night vision devices. They don't cover all of infrared.