Particle characterisation with a focus tuneable lens

The apparatus of any preceding claim, wherein the focus tuneable lens comprises an illumination focus tuneable lens, configured to direct the light beam into the sample.

The apparatus of any preceding claim, wherein the focus tuneable lens comprises a detection focus tuneable lens configured to collect the scattered light for the detector.

The apparatus of any preceding claim, wherein the apparatus may be configured to adjust the illumination focus tuneable lens and detection focus tuneable lens in tandem.

The apparatus of any preceding claim, wherein the location of the scattering volume is adjustable without translating a lens or lens element.

The apparatus of any preceding claim, comprising a detection optical path, by which the scattered light reaches the detector, and an illumination optical path, by which the light beam reaches the sample from the light source, wherein:

• the focus tuneable lens may has an optical axis,
• the detection optical path on the opposite side of the detection focus tuneable lens to the sample is at a first, non-zero, angle to the optical axis,
• the illumination optical path is at a second, non-zero, angle to the optical axis on the opposite side of the illumination focus tuneable lens to the sample.

The apparatus of any preceding claim, configured such that moving the position of the scattering volume in the sample closer to the planar surface by changing the focal length of the focus tuneable lens results in an increase in the scattering volume.

The apparatus of any preceding claim, further comprising a beam splitter, the beam splitter configured to direct some of the illuminating light beam onto the detector to mix with the scattered light from the detection optical path.

The apparatus of any preceding claim, comprising a processor configured to perform a zeta potential measurement based on the output of the detector.

The apparatus of any preceding claim, wherein the focus tuneable lens comprises a deformable lens.

The apparatus of any preceding claim, wherein the focus tuneable lens comprises a material in which a refractive index may be varied by application of a stimulus.

The apparatus of any preceding claim, wherein the focus tuneable lens is arranged to collect at least one of:

• forward scattered light, back scattered light and side scattered light.

A particle characterisation apparatus comprising:

• a light source for illuminating a sample with a light beam;
• a detector arranged to detect scattered light from the interaction of the light beam with the sample;
• and a focus tuneable lens arranged to collect the scattered light for the detector from a scattering volume and/or to direct the light beam into the sample, wherein the apparatus is arranged so that adjustment of the focal length of the focus tuneable lens results in a change in the location of the scattering volume without a change in the angle between the illumination and detection optical paths.

The apparatus of claim 34, wherein both the detection optical path and the detection optical path pass through the focus tuneable lens.