Difference between revisions of "Ultrastable heterodyne interferometry using a modulated light camera"
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− | @ | + | @Article{Patel2014, Title = {Widefield two laser interferometry}, Author = {Rikesh Patel and Samuel Achamfuo-Yeboah and Roger Light and Matt Clark}, Journal = {Opt. Express}, Year = {2014}, Month = {Nov}, Number = {22}, Pages = {27094--27101}, Volume = {22}, Abstract = {A novel system has been developed that can capture the wide-field interference pattern generated by interfering two independent and incoherent laser sources. The interferograms are captured using a custom CMOS modulated light camera (MLC) which is capable of demodulating light in the megahertz region. Two stabilised HeNe lasers were constructed in order to keep the optical frequency difference (beat frequency) between the beams within the operational range of the camera.This system is based on previously reported work of an ultrastable heterodyne interferometer \&\#x0005B;Opt. Express 20, 17722 (2012)\&\#x0005D;. The system used an electronic feedback system to mix down the heterodyne signal captured at each pixel on the camera to cancel out the effects of time varying piston phase changes observed across the array. In this paper, a similar technique is used to track and negate the effects of beat frequency variations across the two laser pattern. This technique makes it possible to capture the full field interferogram caused by interfering two independent lasers even though the beat frequency is effectively random.As a demonstration of the system\&\#x02019;s widefield interferogram capture capability, an image of a phase shifting object is taken using a very simple two laser interferometer.}, Doi = {10.1364/OE.22.027094}, Keywords = {Interferometric imaging ; Interferometric imaging}, Owner = {rp}, Publisher = {OSA}, Timestamp = {2014.11.18}, Url = {http://www.opticsexpress.org/abstract.cfm?URI=oe-22-22-27094}, pdf = { http://optics.eee.nottingham.ac.uk/w/images/4/4d/Pap4.pdf} } |
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− | @ARTICLE{ | + | @ARTICLE{Patel2012, author = {Rikesh Patel and Samuel Achamfuo-Yeboah and Roger Light and Matt Clark}, title = {Ultrastable heterodyne interferometer system using a CMOS modulated light camera}, journal = {Opt. Express}, year = {2012}, volume = {20}, pages = {17722--17733}, number = {16}, month = {Jul}, abstract = {A novel ultrastable widefield interferometer is presented. This uses a modulated light camera (MLC) to capture and stabilise the interferogram in the widefield heterodyne interferometer. This system eliminates the contribution of piston phase to the interferogram without the need for common path optics and results in a highly stable widefield interferometer.The MLC uses quadrature demodulation circuitry built into each pixel to demodulate the light signal and extract phase information using an electronic reference signal. In contrast to the work previously presented \&\#x0005B;Opt. Express 19, 24546 (2011)\&\#x0005D;, the reference signal is derived from one of the pixels on board the MLC rather than an external source. This local reference signal tracks the instantaneous modulation frequency detected by the other pixels and eliminates the contribution of piston phase to the interferogram, substantially removing the contributions of unwanted vibrations and microphonics to the interferogram. Interferograms taken using the ultrastable system are presented with one of the interferometer mirrors moving at up to 85 mm s\&\#x02212;1 over a variety of frequencies from 18 Hz to 20 kHz (giving a variation in optical path length of 220 \&\#x003BC;m, or 350 wavelengths at 62 Hz). This limit was the result of complex motion in the mirror mount rather than the stability limit of the system. The system is shown to be insensitive to pure piston phase variations equivalent to an object velocity of over 3 m s\&\#x02212;1.}, doi = {10.1364/OE.20.017722}, keywords = {Interferometric imaging ; Interferometric imaging}, owner = {rp}, publisher = {OSA}, timestamp = {2013.06.03}, url = {http://www.opticsexpress.org/abstract.cfm?URI=oe-20-16-17722}, pdf = {http://optics.eee.nottingham.ac.uk/w/images/0/0f/Pap3.pdf}} |
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− | @ | + | @ARTICLE{Patel2011a, author = {Rikesh Patel and Samuel Achamfuo-Yeboah and Roger Light and Matt Clark}, title = {Widefield heterodyne interferometry using a custom CMOS modulated light camera}, journal = {Opt. Express}, year = {2011}, volume = {19}, pages = {24546--24556}, number = {24}, month = {Nov}, 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 {\textpm}6.6{\textdegree}. The added value of this method to acquire widefield images are discussed along with the advantages.}, doi = {10.1364/OE.19.024546}, owner = {rp}, publisher = {OSA}, timestamp = {2012.01.13}, url = {http://www.opticsexpress.org/abstract.cfm?URI=oe-19-24-24546}, pdf = {http://optics.eee.nottingham.ac.uk/w/images/d/d6/Pap1.pdf}} |
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Latest revision as of 13:13, 18 November 2014
Ultrastable heterodyne interferometry using a modulated light camera
PhD student: Rikesh Patel
Project Supervisor: Matt Clark
Project Brief:
Interferometry is used in a wide variety of fields for the instrumentation and analysis of subjects and the environment. Captured widefield interference patterns can be used to determine changes in the optical path length of interfering beams across a 2D area. The heterodyne interferometers use light with different optical frequencies to generate a fringe pattern that is modulated at a frequency equal to the optical frequency difference (beat frequency). A widefield heterodyne system is not straightforward to bring into practice, however, it does offer some benefits such as direct phase interpretation and the suppression of low frequency background light in interferograms.
For this project, a widefield heterodyne interferometer system was developed. A custom prototype modulated light camera (MLC) chip was used to capture both homodyne and heterodyne fringe patterns. The 32x32 pixel camera is capable of continuously demodulating incident modulated light at frequencies between 100 kHz and 17 MHz. With modifications to the system, an ultrastable widefield heterodyne interferometer system was implemented. The intention of this system was to eliminate the contribution of piston phase to a captured interferogram without the need for common path optics. In contrast to the standard heterodyne setup, the reference signal used in the demodulation process was derived from one of the pixels on-board the MLC, rather than from an external source. This new local reference signal tracks the common changes in the temporal phase detected by all the MLC's pixels, eliminating piston phase and substantially reducing the contributions of unwanted vibrations and microphonics from interferograms. As an application of the ultrastable system, a novel interferometer has been developed that captures the widefield fringe patterns generated by interfering two independent light sources, rather than by a single split source. The two separately stabilised HeNe lasers, constructed in the laboratory, produce light with a reasonably stable output frequency. Interfering two of these sources produce a heterodyne interference pattern with an unknown beat frequency. The beat frequency continuously varies because of the variation in the output frequency of each laser, but these stabilised lasers produce a beat frequency that drift by as little as 3 MHz over 30 minutes. As the ultrastable system tracks changes in the temporal phase and instantaneous frequency of an incident fringe pattern, it can be used to track the variations in the modulation frequency generated by the fluctuations in the two separate lasers.
Thesis link: PDF
Publications:
Rikesh Patel, Samuel Achamfuo-Yeboah, Roger Light, Matt Clark - Widefield two laser interferometry
- Opt. Express 22(22):27094--27101, Nov 2014
- http://www.opticsexpress.org/abstract.cfm?URI=oe-22-22-27094
BibtexAuthor : Rikesh Patel, Samuel Achamfuo-Yeboah, Roger Light, Matt Clark
Title : Widefield two laser interferometry
In : Opt. Express -
Address :
Date : Nov 2014
Rikesh Patel, Samuel Achamfuo-Yeboah, Roger Light, Matt Clark - Ultrastable heterodyne interferometer system using a CMOS modulated light camera
- Opt. Express 20(16):17722--17733, Jul 2012
- http://www.opticsexpress.org/abstract.cfm?URI=oe-20-16-17722
BibtexAuthor : Rikesh Patel, Samuel Achamfuo-Yeboah, Roger Light, Matt Clark
Title : Ultrastable heterodyne interferometer system using a CMOS modulated light camera
In : Opt. Express -
Address :
Date : Jul 2012
Rikesh Patel, Samuel Achamfuo-Yeboah, Roger Light, Matt Clark - Widefield heterodyne interferometry using a custom CMOS modulated light camera
- Opt. Express 19(24):24546--24556, Nov 2011
- http://www.opticsexpress.org/abstract.cfm?URI=oe-19-24-24546
BibtexAuthor : Rikesh Patel, Samuel Achamfuo-Yeboah, Roger Light, Matt Clark
Title : Widefield heterodyne interferometry using a custom CMOS modulated light camera
In : Opt. Express -
Address :
Date : Nov 2011