Autofocus module and method for a microscope-based system

A microscope system comprising:

• an objective defining an optical axis perpendicular to a surface of a specimen;
• a stage configured to support the specimen and displaceable in a direction of the optical axis;
• and
• an autofocus module including:
• a first light source configured to generate a first light beam for focusing;
• a second light source configured for generating a second light beam for focusing;
• an optical directing device configured to direct a respective portion of each of the first and second light beams onto an incoupling device, the incoupling device being configured to couple the respective portion of each of the first and second light beams into an illuminating light beam of the microscope-based system and direct the respective portion of each of the first and second light beams onto the specimen, the illuminating light beam being perpendicular to a surface of the specimen and propagating along the optical axis;
• a first detector configured to receive a third light beam of the first light source, the third light beam being reflected from the specimen;
• and
• a second detector configured to receive a fourth light beam of the second light source, the fourth light beam being reflected from the specimen.

An method for autofocussing a microscope-based system, the microscope-based system including at least one objective defining an optical axis of the microscope-based system, the method comprising:

• displacing a specimen in a direction of the optical axis and in a vicinity of a region that includes an optimum focal position;
• alternatingly generating a first light beam using a first light source and a second light beam using a second light source;
• directing a respective portion of each of the first and second light beams onto a surface of the specimen using an optical directing device;
• receiving on a first detector light of the first light beam reflected from the surface of the specimen;
• receiving on a second detector light of the second light beam reflected from the surface of the specimen;
• and
• determining the optimum focal position using intensities measured on the first and second detectors.