Widefield heterodyne interferometry using a custom CMOS modulated light camera

Abstract

Abstract:In this paper a method of taking widefield heterodyne interferograms using a prototype modulated light camera is described. This custom CMOS modulated light camera (MLC) uses analogue quadrature demodulation at each pixel to output the phase and amplitude of the modulated light as DC voltages. The heterodyne interference fringe patterns are generated using an acousto-optical frequency shifter (AOFS) in an arm of a Mach-Zehnder interferometer. Widefield images of fringe patterns acquired using the prototype MLC are presented. The phase can be measured to an accuracy of ±6.6 • . The added value of this method to acquire widefield images are discussed along with the advantages.

Widefield two laser interferometry

“…The light sources used are frequency stabilised HeNe lasers using a simple intensity-toheater feedback circuit; the stabilisation technique has no dependence on the other laser. The widefield detector used to capture the heterodyne fringe patterns is a prototype custom CMOS modulated light camera, which was used and analysed in previous work [9,18]. The MLC uses quadrature demodulation, mixing the detected signal (on every pixel) with a reference signal.…”

“…Two laser interferograms appear stable as long as the beat frequency is within the system operational bandwidth, which is dependent on the amplitude/phase/frequency response of the individual components in each pixel. Further details on the MLC is available in a previous publication [9].…”

“…This arrangement is usually only used in single point interferometers due to the practical challenges associated with capturing widefield time varying fringe patterns. However some systems have been developed to capture real time heterodyne interference patterns in the widefield region at modest modulation frequencies [5][6][7][8][9]. In a previous paper [9], we demonstrated that this could be accomplished for the widefield in the megahertz frequency range using a prototype modulated light camera (MLC).…”

New developments in ultrasound-modulated optical tomography made by heterodyne holography

“…1 (b) ). To evaluate the performances of the pulsed setup, we have performed simulations by considering either a regular camera, or a lock-in cameras, similar to the ones recently developed [5][6][7] or commercially available (e.g. heliCam TM C3, Heliotis).…”

Bit-efficient, sub-millisecond wavefront measurement using a lock-in camera for time-reversal based optical focusing inside scattering media

“…In this work, we developed a wavefront measurement method based on a lock-in camera [17,18] (heliCam C3, Heliotis; 300 × 300 pixels), in which each pixel performs analog lock-in detection and outputs only the information of the AC signal ( S AC ) at up to 3800 frames per second to an on-chip memory. Specifically, the lock-in circuitry generates the in-phase ( $S_{\mathrm{I}}false(rfalse)\propto 2\sqrt{I_{\mathrm{normalR}}{I}_{\mathrm{normalT}}(\overrightarrow{r})}sinfalse[false({\phi }_{\mathrm{T}}false(\overrightarrow{r}false)-{\phi }_{\mathrm{R}}+\pi /4false)false]$) and the quadrature ( $S_{\mathrm{Q}}false(rfalse)\propto 2\sqrt{I_{\mathrm{normalR}}{I}_{\mathrm{normalT}}(\overrightarrow{r})}cosfalse[false({\phi }_{\mathrm{T}}false(\overrightarrow{r}false)-{\phi }_{\mathrm{R}}+\pi /4false)false]$) components of the AC signal oscillated at the frequency of f b , which are then digitized by a 10 bit ADC.…”