Apparatus and method for focusing a laser scanning cytometer

A method for performing a laser-based measurement, said method comprising,

• changing a distance along an optical axis between an objective and a substrate to establish a plurality of focal distances,
• transmitting laser light through said objective along said optical axis at said plurality of focal distances onto said substrate at each of a plurality of locations, wherein the substrate has a periphery and at least one of the plurality of locations is within the periphery of the substrate,
• receiving a plurality of reflected components of said laser light through said objective at each of said plurality of locations, wherein each of said plurality of reflected components is received at a corresponding one of said plurality of focal distances and from a corresponding one of said plurality of locations,
• processing said plurality of reflected components corresponding to each of said plurality of focal distances at each of said plurality of locations to determine said optimal focal distance for each of said plurality of locations,
• storing a representation of said optimal focal distance for each of said plurality of locations,
• introducing a sample onto said substrate,
• measuring a characteristic of said sample by,
• selecting a measurement location on said substrate,
• selecting a focal distance for said objective based at least in part on said stored representation, and
• performing a laser-based measurement on said sample at said measurement location and at said selected focal distance, and
• performing said measuring step at additional measurement locations.

A system for determining an optimal focal distance, said system comprising,

• a laser source adapted to provide laser light,
• an objective adapted to direct said laser light at a plurality of focal distances onto a substrate at each of a plurality of locations, and to receive a plurality of reflected components of said laser light at each of said plurality of locations, wherein each of said plurality of reflected components is received at a corresponding one of said plurality of focal distances, and from a corresponding one of said plurality of locations and wherein the substrate has a periphery and at least one of the plurality of locations is within the periphery of the substrate,
• a driver adapted to establish said plurality of focal distances by adjusting a distance along an optical axis between said objective and said substrate,
• a processor, adapted to process said plurality of reflected components corresponding to each of said plurality of focal distances at each of said plurality of locations to determine said optimal focal distance for each of said plurality of locations.