System for measuring optical forces acting on a particle by using a single light beam (120, 124) to trap the particle by the use of high gradient forces, the system comprising: a light source for generating the single light beam, the light source being a laser source and the single light beam being a laser beam, a telescope having an eye piece lens and an objective lens located in the optical path of the laser beam, the objective lens being to recollimate and expand the laser beam, a chamber containing a suspension medium between an entry cover of the chamber and an exit cover of the chamber, the chamber being for suspending the particle in the suspension medium; a high numerical aperture trap objective immersion lens to focus the single light beam down to a diffraction-limited spot onto the suspended particle in a manner to cause light beam photons to trap the particle by use of high gradient forces, and comprising an entrance pupil, a series of internal lenses and an exit lens that interfaces with the entry cover of the chamber via an immersion medium; a high numerical aperture collection immersion lens having a numerical aperture greater than or equal to the index of refraction of the medium that suspends the particle within the chamber, and comprising a front lens that interfaces with the exit cover of the chamber via an immersion fluid of high refractive index; a light sensing device located in the downstream optical path of the collection lens; wherein the collection lens is positioned and used to capture photons from the single light beam that are deflected by the particle and photons from the single light beam that are not deflected by the particle; the collection lens further comprises a series of internal lenses to collimate and direct the captured photons towards the light sensing device; the working distance (w) between the exit cover and the front lens of collection lens is between 1 millimeter and 3 millimeters; and the light sensing device is placed at the back focal plane of the collection lens or at an optical equivalent thereof, in order to obtain the force acting on the trapped particle by adding up the individual momentum changes of all the photons in the light imaged onto the light sensing device. a light source for generating the single light beam, the light source being a laser source and the single light beam being a laser beam, a telescope having an eye piece lens and an objective lens located in the optical path of the laser beam, the objective lens being to recollimate and expand the laser beam, a chamber containing a suspension medium between an entry cover of the chamber and an exit cover of the chamber, the chamber being for suspending the particle in the suspension medium; a high numerical aperture trap objective immersion lens to focus the single light beam down to a diffraction-limited spot onto the suspended particle in a manner to cause light beam photons to trap the particle by use of high gradient forces, and comprising an entrance pupil, a series of internal lenses and an exit lens that interfaces with the entry cover of the chamber via an immersion medium; a high numerical aperture collection immersion lens having a numerical aperture greater than or equal to the index of refraction of the medium that suspends the particle within the chamber, and comprising a front lens that interfaces with the exit cover of the chamber via an immersion fluid of high refractive index; a light sensing device located in the downstream optical path of the collection lens; wherein the collection lens is positioned and used to capture photons from the single light beam that are deflected by the particle and photons from the single light beam that are not deflected by the particle; the collection lens further comprises a series of internal lenses to collimate and direct the captured photons towards the light sensing device; the working distance (w) between the exit cover and the front lens of collection lens is between 1 millimeter and 3 millimeters; and the light sensing device is placed at the back focal plane of the collection lens or at an optical equivalent thereof, in order to obtain the force acting on the trapped particle by adding up the individual momentum changes of all the photons in the light imaged onto the light sensing device.