system
Given the following post, respond as if you're commenting on Reddit:
human
What are the differences between an expensive laser diode used for scientific applications and a cheap consumer grade laser pointer ?
gpt
The term "scientific laser" is pretty broad, and encompasses many different technologies and requirements for many different scientific purposes.

Generally, two things drive the cost of a laser system:

1) Sustained (not peak) power output

2) Beam coherence (how little the beam spreads out over distance)

The two things that are common to most consumer laser pointers are that they are very low power (by design, for safety reasons), and they usually have pretty bad coherence (by design, because highly coherent lasers are expensive). The optical components tend to be integrated into the silicon itself or made from cheaper to manufacture plastic. 

Depending on the needs of the scientific laser, you might need high power, high coherence, or both. Higher power lasers quickly start to need special cooling apparatus and all of the optical components need to be made of higher quality materials and with better workmanship, lest they absorb too much laser light and overheat. Higher coherence lasers need precision crafted lenses and mirrors that are adjusted to keep the beam tightly confined. 

For examples, a high(er) power but low coherence laser might be found in an astronomical laser pointer used for education and teaching. A low power but high coherence laser might be found in measurement devices. A high power, high coherence laser might be found in a laser cutter. 

One thing that makes many scientific lasers expensive is not their performance, but rather their calibration. The laser is adjusted and certified by the manufacturer to have a certain output behavior. The technology itself is not necessarily more complicated in this case, but the warranty by the manufacturer that it is suitable for a specific purpose is expensive. There are also many peripherals you find in scientific laser applications, such as cooling for continuous operation, or data measurement and acquisition hardware/software, that aren't present in a consumer grade product.

There are a few well known scientific lasers that are designed to achieve very high peak power, versus sustained power. An example of this is the laser used at the National Ignition Facility to do fusion power research.