Mode-switchable illumination system for a microscope

1. An illumination system for a microscope system capable of being mode-switchable between a first and a second illumination mode comprising:

one source of light for providing a collimated beam of light;

at least one selector mirror capable of being positioned in at least two positions to redirect the beam of light in two different beam paths,

the first beam path being a direct exit beam path wherein the selector mirror redirects the beam of light along an exit beam path to provide a first illumination mode,

the second beam path being a mirror loop path comprising two or more mirrors wherein the selector mirror redirects the beam of light along the exit beam path after first redirecting the beam of light to one of the two or more mirrors and after one of the two or more mirrors redirects the beam of light back to the selector mirror,

wherein the first mirror loop path comprises at least one optical element arranged to optically alter the beam of light to provide the second illumination mode, and

wherein the selector mirror is arranged to provide selective scanning of the beam of light in a first dimension; and

a scan mirror arranged at the exit beam path to provide selective scanning of an output beam of light, and

wherein the illumination system further comprises a second mirror loop path selectively addressed by the scan mirror and comprising two or more mirrors arranged to redirect the beam of light onto the scan mirror such that it is redirected by the scan mirror a second time along the exit beam path, whereby the exit beam is scanned by a parallel translation, and

wherein the scan mirror is arranged to provide selective scanning in a second dimension essentially transverse to the first dimension, and the mutual scanning of the scan mirror and the selector mirror is controlled to provide 2-dimensional scanning of the output beam of light.

2. An illumination system of claim 1 , wherein the first mirror loop path comprises an extended mirror loop to provide a predetermined beam path length with respect to the optical element.

3. An illumination system of claim 1 , comprising at least one exit optical element which is optically matched and positioned with respect to the at least one optical element in the first mirror loop path, and arranged to optically alter the beam of light to provide the first and second illumination modes.

4. An illumination system of claim 3 , wherein the exit optical element is an exit lens arranged to focus the beam of light at the back aperture of an objective of a microscope system, and wherein the optical element in the first mirror loop path is a lens arranged to focus the beam of light at a predetermined point along the beam path before the beam of light reaches the exit lens whereby the beam of light is re-collimated.

5. An illumination system of claim 1 , wherein the first illumination mode is Total Internal Reflection (TIRF) and the second illumination mode is Photokinetics (PK) illumination.

6. A microscope system comprising the illumination system of claim 1 .