Although Einstein did not invent the laser pointer, his work laid the foundation. Einstein pointed out that stimulated emission of radiation may occur together with spontaneous emission and absorption. He used photon mathematics to study the situation of a large number of atoms full of excess energy, and prepared to emit photons in random directions at a random time. If a stray photon passes, the atom will be stimulated by its existence and emit its photon early. What's more noteworthy is that the emitted photon propagates in the same direction as the original photon and has exactly the same frequency! Later, when a small group of the same photons pass through the remaining atoms, more and more photons will leave their atoms earlier and enter the subatomic parade.
Schawlow found the key-put the atoms to be excited in a long and narrow cavity with a mirror at each end. The rays will shuttle back and forth inside, thereby having more opportunities to excite atomic radiation. One of the mirrors is only partially silver-plated, so some light may leak out. This arrangement (Fabry-Perot etalon) is familiar to generations of optical researchers.
At the same time, Gordon Gould, a graduate student at Columbia University, had discussed this issue with Townes. For his thesis research, Gould is already studying "pumping" atoms to a higher energy state so that they can emit light. When Gould elaborated on his ideas and thought about all the things that could be done with a spotlight, he realized that he was in a position far beyond the "infrared pulse" people were discussing. In his notebook, he confidently named the uninvented device laser engraver (for optical amplification by stimulated emission).
Lasers have become an essential part of many applications and industries, amplifying the effects of magical light. Data from research and analysis company Gartner shows that today, laser-driven lithography plays a key role in semiconductor manufacturing, with total revenue of $477 billion in 2018. Laser-based ranging systems provide the information needed for safe navigation of autonomous vehicles. For such vehicles, today’s market is small, but the forecast of AMR shows that by 2026, the size of the market will reach 550 billion US dollars. The medical laser market-including solid-state and gas laser systems, dye laser systems and diode lasers. According to AMR, the total price of these systems will be between US$1.2 and 13 billion by 2023. Popular medical applications include cardiovascular, dermatology, and eye-related treatments. Finally, the networking giant Cisco predicts that by 2022, the data center and long-distance fiber market for blue laser pointer and optical connections carrying data traffic will decrease by an average of 26% per year.