Laser spectrum range What are the spectrum limits in which a laser can be produced? Also can you focus other electromagnetic waves (microwaves, radio waves, ect…) into a laser like beam?
 A: Actually, the first "laser" (1954) was emitting microwaves. Charles Townes wanted to produce a microwave source with a very narrow linewidth and came up with the idea to separate ammonia molecules residing in the upper component of the inversion splitting from those residing in the lower component using a hexapole. In this way, he was able to obtain the required population inversion for laser action. He named the apparatus "Microwave Amplification by Stimulated Emmission of Radiation" or MASER. Later on (1960), stimulated emission was used in Ruby crystals by Maiman to produce an optical maser or laser. Townes wrote an interesting account on his personal experiences in "How the laser happened".
Since the early days of the laser, the frequency range has been extended quite a lot. The invention of dye lasers introduced lasers that can typically scan tens of nanometers in the near infrared, visible and near UV part of the spectrum by using population inversion in organic dyes. Also, excimer lasers using excited states of certain gasses to produce high energy radiation in the UV are commonly available. Solid state lasers like the ones using titanium sapphire crystals reach wavelengths from roughly 700 to 1000 nm. In addition, nonlinear optics allows one to double the frequency of a laser extending its domain. 
Nowadays, quantum-cascade lasers (mostly in the infrared) and diode lasers are the state of the art. They are turn key and can be produced at many different wavelengths. However, their scanning capability is very narrow as compared to a dye laser. 
You might find it interesting to know that masers do also exists in nature. In space, methanol and OH masers, for instance, are among the brightest radio sources in the sky.
A: Extending @Paul's excellent answer, here is the upper limit.
Gamma lasers, alias grasers are planned by induced gamma emission in nuclear isomers. They won't be coherent.
Free electron lasers can produce coherent röntgen beams.
