Light sources Excitation light must be focused to a diffraction limited spot Excitation light Could be done with an arc lamp and pinhole-but very inefficient Enter the laser: Perfectly collimated and Objective lens high power SampleLight sources Sample Objective lens Excitation light Excitation light must be focused to a diffraction limited spot Could be done with an arc lamp and pinhole – but very inefficient Enter the laser: Perfectly collimated and high power