Q1 (30/100) We often use laser diodes to excite biological samples and observe their fluorescence emission. Figure 1 shows a transfer function (the laser output power P vs the driving current

/) of a laser diode, where you can see that a typical laser has three different operation regions (taking the transfer curve at 0 °C as an example): Sub-threshold: the laser operates below the threshold current, Ith, emitting minimal light; Linear region (this is where the laser usually operates): the driving current is higher than the threshold, the laser shows the best efficiency; Saturation: the driving current is too large, and the efficiency drops again (note the behaviour in this region is not linear, but let's approximate it with a straight line for simplicity). i) iii)