More specifically, let's assume we're firing a laser 50 microns in diameter at a block of steel 10 cubic meters in size and this laser delivers 1 megajoule of energy during the entire length of time it's active. How different is the observable effect on the block if this laser pulse takes 1 second to deliver that megajoule (and then shuts off) vs. doing so in 1 millisecond vs. 1 nanosecond? Does this affect how large a section of the block melts or vaporizes, or how much superheated plasma might be sent flying around the room where this was happening, despite the total amount of energy being applied to the block being the same? (Or how much air ionizes in the laser's path, for that matter)
From my limited understanding of the problem, the vaporization of material impacted by the photons will create plasma that then shields the material immediately behind it from the laser's effects to some degree (by scattering the photons?), and I assume the time interval affects how much time this plasma has to scatter and disperse, but presumably if the plasma hasn't had time to disperse, it simply grows hotter and hotter itself as it absorbs the laser's energy and shouldn't this make it scatter faster anyway? How much would this superheating counteract the smaller window of time for molecules to move (assuming I'm not totally off-base with my understanding here)
The plasma would also transfer heat to the surrounding steel via convection too, yes? Is heat transferred this way rate-limited in some fashion that would mean that slower laser pulses tend to diffuse heat over a larger area of steel than faster pulses? Or is even 1 second far too little time to transfer enough heat to melt an appreciable section of the block not in close contact with the laser itself?
Are there any other major factors here I have overlooked?
My background is not in physics (I'm doing research for a novel, actually), so I apologize for any crudeness or misunderstandings in the above text, and I don't need exact calculations, but even a general understanding of how rate of energy application affects heat diffusion and material ablation would be very helpful.