Frankly, from the pov of a biologist I doubt this will work. The mechanism detects turbulence patterns in the blood. But so many factors influence the mechanics of blood flow: hormones and certain illnesses as well as age render blood vessels thinner along the wall and/or clogged on the inside), aneurysms will alter the blood current patterns and some medication (blood thinners, for example) will alltogether alter the way the blood's flowing behaviour. An injury and the resulting scar or a few blocked capillaries (for example with diabetics) can also change the blood flow and consequently the turbulence patterns in the flowing blood.
Also - faint hearted men continue reading at your own risk! - women who are pregnant or have their period will have different flow patterns from day to day and thus register false signals. The same goes for females suffering from endometriosis or cysts and for both genders that have any other growths that change the blood flow physically.
When we get older, the Valvula Venosa (my appologies - I couldn't find out what they are called in English, so I must use the medical term) start to slacken which we notice when the blood remains in our legs and can't be pumped upwards again. This, too, changes the currents in the blood and the laser will not recognize the person anymore.
There are too many variables to be taken into consideration for such a device to work with the required accuracy.