My opinion is that regardless of what we try the Chinese tube will always be just a Chinese tube.
There is a lot of research to be done if you want to get a real answer on how to get the best performance out of the tube. A manufacturer specs it as 1ms rise time: http://laser-cn.en.made-in-china.com/of ... -40W-.html
If you take a close look at the manual you will see that they also hold the 1ms rise time:http://www.jinlantrade.com/eBay/40W%20L ... Manual.pdf
We have a choise, either use a pwm signal to charge an rc circuit
I never figured out why people started using rc + pwm to control laser power since it is a very suboptimal solution. If you have a digital signal to begin with and the laser is designed to take a digital signal why put a low pass filter between the two?
You could alternatively use the power supply the way it was designed, namely use the potentiometer to set the maximum current and then provide a 20-50KHz PWM signal through the TTL input as specified in the manual. If you do the math, with a 1ms rise time you can shove a crapload of pulses into the power supply and even a single pulse would be enough since hopefully one would have 8 bit or higher control.
I have no reason to believe this isn't the best way since the retina engrave uses a 20KHz PWM signal and can vary power while engraving no problem (my potentimeter always stays at maximum and when doing a low power engraving the PWM signal just reduces the duty cycle of the dots that need to be engraved).
The retina is fully capable of grayscale engravings and they have addressed it in the past:http://www.fullspectrumengineering.com/ ... rt=30#p568
The short version is that nobody does grayscale engraving since materials don't respond as consistently and to your eye there would be no advantage (any form of printed media is dithered). Inkjets use dithering (its not like you can apply a "lighter" dot of colour, the droplet is either there or it isn't) and the visual quality is fine.