# Why did the Maser amplify microwaves and not visible light?

The first "Laser", the Maser, amplified stimulated microwave emissions, rather than visible light that is the most common thing today. Why?

If we take a simple example, and consider the ratio of the rate of spondaneous emission and stimulated emission

$$Ratio = \frac{R_{spont.}}{R_{stim.}} = e^{\frac{h\nu}{kT}} -1$$

Comparing two different cases: 1) a microwave source operating at a frequency of $10^{10}$Hz and at 300K, and 2) a tungsten lamp with operating at a frequency of $5\times10^{14}$ at 2000 K. The ratios become $R_{Tungsten} = 163605$ and $R_{Microwave} = 1.60198\times 10^{-9}$. So, clearly, the probability of stimulated emission is much higher for longer wavelengths.

Using these results, why did the Maser come before the Laser? I can understand that perhaps the Maser resulted in a higher intensity beam than a Laser would at that time, but I suppose they could still make a working Laser.