To use the pulse beam, you do two taps, then hold for up to a max of 4 seconds. Your damage in that time is based on the damage of the two taps, plus some number of pulses. The number of pulses you get goes like this:
PULSE INFO ONLY INCLUDING INITIAL TAPS
Hold Duration Pulses Total Time Total Hits Damage/Combo Damage/10s Ratio vs. RMB spam
1 second 2 2 seconds 4 41 207 x0.85
1.5 second 4 2.5 seconds 6 62 249 x1.03
2 seconds 6 3 seconds 8 83 277 x1.14
2.5 seconds 8 3.5 seconds 10 104 296 x1.22
3 seconds 10 4 seconds 12 124 311 x1.29
3.5 seconds 12 4.5 seconds 14 145 323 x1.33
3.9 seconds 13 4.9 seconds 15 156 317 x1.31
3.95+ seconds 24 5 seconds 26 270 539 x2.23
The key information is that you really need to hold it for the full 4 seconds to get the real damage output.
The first 1 second hold is basically just 2 pulses, like the normal ranged tap but without the bonus damage on the 3rd tap, so it comes out WORSE than just range tap spam.
After the first 1 second, you get a pulse every 0.25 seconds, so with a 1.5 second hold you catch up to normal ranged tap spam, and then start improving past it. But even if you get up to a 3.5 second hold the damage isn't really that great, maxing out at a x1.33 ratio over ranged tap spam.
However, if you hold it for the full duration, you would normally get 14 pulses. However, as soon as you get the 14th pulse, you get an EXTRA free 10 pulses without any animation, for an actual total of 24 pulses (plus the initial 2 taps, so 26 damage numbers). At that point, the ratio is over x2.2 the basic ranged attack.
I've also tested it by throwing in another power (both Swoop Attack and my basic heal) right at the 4 second hold mark, and it will do the subsequent action while still giving you the full 24 pulses.