The function of the laser diode in a banknote detector

We use a laser to create covert codes on the printed banknote. Magnetic code in security threads ranges from simple yes/no recognition to complex coding (MultiCode™). The Apex 7000 uses magnetic detection to accurately authenticate bills while providing efficient acceptance of non-counterfeit bills. When electric current flows through the p-n junction, the gain is. The laser diode chip is the small black chip at the front; a photodiode at the back is used to control output power. The anode connection on the right has been accidentally broken by the case cut. The symbol of the laser diode resembles LED except it has an extra vertical line in it as shown below. [pdf]