Optical system comprising: - an input optical field-splitting means (140, 313, 333) configured to receive an input optical field and to provide at least a sample illumination optical field propagating along a first optical path (230, 341) and at least a reference optical field propagating along a second optical path (220, 342); - a first pupil splitting or modification means (160, 312, 314) and a first hole-reflector (123, 124, 315) arranged to channel or direct a back-reflected optical field to a detection or collection area (130, 307, 407) from a sample (120,303) to be investigated; - a second pupil splitting or modification means (160, 170, 312, 324) and a second hole-reflector (124, 123, 335) arranged to channel or direct the reference optical field to the detection or collection area (130, 307, 407); the first pupil splitting or modification means (160, 312, 314) and the first hole-reflector (123, 124, 315) being arranged to channel or direct the sample illumination optical field to the detection or collection area (130, 307, 407) without directing the sample illumination optical beam (i) through the input optical field-splitting means or (ii) through a further optical field-splitting means located downstream of the input optical field-splitting means (313, 333), and/or the second pupil splitting or modification means (160, 170, 312, 324) and the second hole-reflector (124, 123, 335) being arranged to direct the reference optical field to the detection or collection area (130, 307, 407) without directing the reference optical field (i) through the input optical field-splitting means or (ii) through a further optical field-splitting means located downstream of the input optical field-splitting means (313, 333), characterized in that the first pupil splitting or modification means (160, 312, 314) is configured to generate a Bessel beam that is propagated to the sample (120, 303, 401) to be investigated via reflection by the first hole-reflector (123, 124, 315), or configured to deviate an optical light field of the sample illumination optical field into a ring-shaped optical light field (232, 234, 380) that is propagated to the sample (120, 303, 401) to be investigated via reflection by the first hole-reflector (123, 124, 315); or in that the second pupil splitting or modification means (160, 170, 312, 324) is configured to generate a Bessel beam that is propagated to the detection or collection area (130, 307, 407) via reflection by the second hole-reflector (124, 123, 335, 435), or configured to deviate an optical light field of the reference optical field into a ring-shaped optical light field (222, 224) that is propagated to the detection or collection area (130, 307, 407) via reflection by the second hole-reflector (124, 123, 335, 435). - an input optical field-splitting means (140, 313, 333) configured to receive an input optical field and to provide at least a sample illumination optical field propagating along a first optical path (230, 341) and at least a reference optical field propagating along a second optical path (220, 342); - a first pupil splitting or modification means (160, 312, 314) and a first hole-reflector (123, 124, 315) arranged to channel or direct a back-reflected optical field to a detection or collection area (130, 307, 407) from a sample (120,303) to be investigated; - a second pupil splitting or modification means (160, 170, 312, 324) and a second hole-reflector (124, 123, 335) arranged to channel or direct the reference optical field to the detection or collection area (130, 307, 407); the first pupil splitting or modification means (160, 312, 314) and the first hole-reflector (123, 124, 315) being arranged to channel or direct the sample illumination optical field to the detection or collection area (130, 307, 407) without directing the sample illumination optical beam (i) through the input optical field-splitting means or (ii) through a further optical field-splitting means located downstream of the input optical field-splitting means (313, 333), and/or the second pupil splitting or modification means (160, 170, 312, 324) and the second hole-reflector (124, 123, 335) being arranged to direct the reference optical field to the detection or collection area (130, 307, 407) without directing the reference optical field (i) through the input optical field-splitting means or (ii) through a further optical field-splitting means located downstream of the input optical field-splitting means (313, 333), characterized in that the first pupil splitting or modification means (160, 312, 314) is configured to generate a Bessel beam that is propagated to the sample (120, 303, 401) to be investigated via reflection by the first hole-reflector (123, 124, 315), or configured to deviate an optical light field of the sample illumination optical field into a ring-shaped optical light field (232, 234, 380) that is propagated to the sample (120, 303, 401) to be investigated via reflection by the first hole-reflector (123, 124, 315); or in that the second pupil splitting or modification means (160, 170, 312, 324) is configured to generate a Bessel beam that is propagated to the detection or collection area (130, 307, 407) via reflection by the second hole-reflector (124, 123, 335, 435), or configured to deviate an optical light field of the reference optical field into a ring-shaped optical light field (222, 224) that is propagated to the detection or collection area (130, 307, 407) via reflection by the second hole-reflector (124, 123, 335, 435).