thinking about this,,,, a room motion sensor does not require something on the other side, but the object itself is the 'other side'
radar works in a similar way, send a signal out and listen for the echo
laser range finders run in the 1 to 10 hz range.
it appears that the answer to the subject line is a simple no, cannot be done. whatever 'breaks the beam is 'the other side'
the actual project seems to be, can I measure a falling object with a sensor.
the answer to that is yes, multiple technologies.
next question is can it report an object within milliseconds.
how far away is the object ? greater distance, longer response time, even at the speed of light.
speed of the object is based on simple calculations. distance from the release point to the plane of the sensor. the maximum speed was revealed by Newton. the object will fall at 32 fps ps until it reaches terminal velocity for the object. terminal velocity will have both resistance and air density. a feather has high resistance, a vacuum has no density. 1,000,000 times zero yields the same result a 1 times zero.
a single sensor above the focal point with the expectation that by the time the sensing and calculations are done, the object will have fallen x mm more would require setting a value for the resistance (assuming standard air density = 70°F, 50% rh, 29.92 in hg) distance is key as well.
so, the question really being 'how can I detect at high speed, a falling object "
I would look towards what a projection line does for sugar or nuts. as the product falls over a sensor, the sensor looks at the object, determines if it is correct, then uses a puff of air to blow nonconforming parts out of the main steam.
may I offer that it is easier for us to help you when we have a goal. just asking if one type of sensor can do one thing will immediately exclude all the depth of knowledge of the community.
quite simply, the only possible answer to your question is no. it is not possible. the object breaking the beam is the other side, therefor your question is faulty.
reading the responses, the community has pretty much ignored the wording of your question. partly because we do not like 'no' as an answer and partly because you have altered it with with more information. And the community has chosen to offer solutions to the actual un-asked question.