Here is another epic demonstration by the popular The Action Lab YouTube channel. In this video, he shows that it is possible to make a decently high resolution microscope with just a laser and a drop of water. This only works with a laser because it is in phase (waves are all inline with each other), doesn't spread out quickly, and is all of the same frequency, which makes a coherent diffraction pattern. By shining a laser at the end of a water dropper/plastic syringe, the laser light diffracts when striking the microscopic objects in the water until it strikes the room wall. Note that the water drop itself acts as a lens to spread out the laser light. The resulting projection is a literal real-time microscope of the contents in the water drop. Tiny bacteria and spores in the water can be seen moving about on the projection. Around the objects can be seen the destructive / constructive wave interference patterns from the diffraction.
The quality of the projection is almost as good as a conventional microscope! However, since the particles in the drop of water are in different 3D positions, the diffraction projection may be smaller or larger depending on the positions. Nonetheless, it gives a qualitative way of analyzing the contents inside the water. Epic stuff!
