Pulsed Laser Interferometry Research Articles

Dynamic imaging of micro-vibrations with an ultra-wide bandwidth and a femtometer noise using switchable pulsed laser interferometry

Imaging the complex dynamics of micro-vibrations plays a fundamental role in the investigation of microelectromechanical systems (MEMS). However, it remains a challenge for achieving both a wide bandwidth and a low noise due to the high photodetector noise and electromagnetic interference at GHz frequencies. Here, we propose a pulsed laser interferometry system with an adaptable switch to image GHz vibrations based on stroboscopic mixing, while measuring lower-frequency vibrations based on the homodyne scheme. The noise power spectral density is shown in both regions from DC to 10 GHz with an average noise down to 30.8 fm/√Hz at GHz frequencies, which holds the highest resolution to the best of our knowledge. Vibrational amplitude and phase mappings of a kHz comb-drive resonator, a GHz piezoelectric transducer, and a GHz film bulk acoustic resonator are presented with animated visualizations and k-space analysis, paving a new paradigm for the first time to image and analyze various MEMS devices of a bandwidth spanning 10 orders of magnitude.

Spatiotemporal visualization of a surface acoustic wave coupled to magnons across a submillimeter-long sample by pulsed laser interferometry

Spatiotemporal visualization of a surface acoustic wave coupled to magnons across a submillimeter-long sample by pulsed laser interferometry

Effect of pulse asymmetry and nonlinear chirp on the accuracy of ultrafast pulsed laser interferometry.

Ultrafast pulsed laser interferometry (PLI) can measure picometer displacements at sub-nanosecond time scales, such as acoustic waves and vibrations in microstructures. In this Letter, the effects of pulse characteristics on the accuracy of PLI are investigated through measurements and modeling. The results show that the effective wavelength of PLI, λeff, varies significantly as a function of overlap between the interfering pulses due to pulse asymmetry and nonlinear chirp. This variation presents a serious limitation on the accuracy of PLI if unaddressed. However, it is shown that a continuous-wave laser interferometer can be used to determine λeff with an uncertainty near 0.01%, making it possible to use PLI for accurate displacement measurements.

Pulsed laser interferometry with sub-picometer resolution using quadrature detection.

Femtosecond pulsed laser interferometry has important applications in measuring picometer-level displacements on sub-nanosecond time scales. In this paper, we experimentally examine its achievable displacement resolution, as well as the relationship between the laser's optical spectrum and the interferometer's effective wavelength. The resulting broadband displacement noise and noise floor of the pulsed laser Michelson interferometer are equivalent to that achieved with a stabilized continuous wave HeNe laser, where values of 1.01 nm RMS and 27.75 fm/√Hz have been demonstrated. It is also shown that a single effective wavelength can accurately describe the fringes of the pulsed laser interferometer but the effective wavelength value can only be determined from the optical spectrum under certain conditions. These results will be used for time-resolved displacement metrology with picosecond temporal resolution in the future.

Quantitative measurement feasibility for 3D distributions of hydrodynamic quantities in the turbulent mixing zone of two gases

In doing research on the turbulent mixing (TM) of two gases different in density, it is of great interest to study experimentally the 3D density distribution pattern of chemically nonreactive gases in the TM zone. For this purpose, noncontact and, particularly, optical techniques to obtain experimental data may be attractive. This article discusses the possibility of using pulsed laser interferometry in this application. Based on this technique, the experiment should result in the mixture density distribution integrated along the light path. Requirements for high-quality interference patterns have been analyzed in application to typical experimental conditions, to show that they may be produced with specific restrictions set on the mixture constitution. Generally, the TM zone has no symmetry. Therefore, the problem of reconstructing 3D density distributions (TDD) of gases can be solved by sufficiently providing many TM zone integral projections (or aspects). It is technically difficult and expensive to achieve this large number of aspects (N> 10). Therefore, it is essential that a reconstruction method be selected to allow the solution of the problem with the least possible number of aspects. Given that the experiment data are incomplete, the reconstruction methods that are based on the concept of maximum data entropy did well. Information a priori about the solution to be sought for an isobaric gas mixture is that its each constituent has invariable density. Thus, a functional data entropy can be defined that is similar to Fermi gas in statistical physics. An algorithm has been suggested for reconstruction as a modified maximum-bounded entropy procedure (Bashurin et al. 1995). This makes reasonable good reconstruction achievable even with as few aspects as N = 4. Experiments on the study of TM of a propane jet in air using a four-aspects laser interferometer were provided and reconstruction of propane concentration distribution was conducted. The results allow determination of the TM zone spectral characteristics.

A two-shutter camera for pulsed laser holography and interferometry using thermoplastic hologram processing

One of the most limiting experimental drawbacks in ruby laser holography and holographic interferometry is that experiments normally have to be performed in darkness. This is due to the fact that the photosensitive materials must not be exposed to background light. To overcome this, a closed holocamera with optical shutters has been designed, constructed and tested. The closed camera system allows the registration and processing of holograms without reducing the normal level of background light illumination.

Pulsed-mode laser Sagnac interferometry with applications in nonlinear optics and optical switching

A Sagnac interferometer (SI) has been constructed with a mode-locked Nd3+:YAG laser as its source. The advantages in pulsed laser interferometry of using a SI over a Mach-Zehnder interferometer are analyzed. The autostability property of SI is experimentally demonstrated. Applications of an SI to light-induced index of refraction change measurements and to the picosecond optical switching are discussed. Experimental results are presented.

1] Pulsed laser interferometry in the ultracentrifuge

This chapter presents two experimental arrangements to describe the role of pulsed laser light in the ultracentrifuge: one arrangement employs a pulsed argon ion laser of moderately high intensity, while the other modulates a low power helium–neon gas laser either externally with a Pockel cell or by means of internal switching. Both arrangements make possible the illumination of (tangentially) selected regions of the rotor and cells. The Pockel cell modulation system makes possible finer control of the region to be illuminated because of its shorter pulse length, down to 0.8 μsec compared to the ∼6 μsec for the unmodified pulsed argon ion laser. The argon ion laser emits significantly higher light intensity than the He–Ne lasers used and, in addition, can provide a number of laser lines in the green and blue region of the spectrum. The pulsed argon ion laser system is also described in the chapter. Studies show that the pulsed argon ion laser is promising as a light source for real-time data acquisition with the Rayleigh optics.

An optical pulse modulation system for laser interference studies in the analytical ultracentrifuge

The mode of operation and construction of a high-speed laser light modulator is presented that is designed for use with the analytical ultracentrifuge. The system may be used with continuous wave lasers having optical powers not exceeding 100 W and has an optical bandwidth from 200 nm to 800 nm. The electronic modulation circuitry described is capable of producing optical pulses of 0.8 μsec duration at a firing frequency in excess of 100,000 pps and is designed to permit the laser source to operate in either a pulsed or nonpulsed mode. The unit is extremely versatile, and its characteristics permit full advantage to be taken of pulsed laser interferometry in the ultracentrifuge.

Pulsed laser interferometry (PLI) in the analytical ultracentrifuge: II. Clocked trigger circuit

A circuit is presented for a digital time delay generator that has been designed to trigger a pulsed argon laser installed for interferometry in the analytical ultracentrifuge. This circuit utilizes a quartz crystal clock to provide a uniform precision of 0.5 μsec in the timing of trigger pulses to the laser. The maximum trigger frequency has been limited to 60 Hz, which cannot be exceeded by the laser. A preset counter can be set for the desired number of laser pulses and alternate trigger pulses can be synchronized to illuminate the contents of any two rotor holes. Several sources of jitter in the timing of the laser are discussed.

Pulsed laser interferometry (PLI) in the analytical ultracentrifuge: I. System design

A description is given of a pulsed argon ion laser light source that is synchronized with rotor orientation in the analytical ultracentrifuge. The system described provides improved fringe contrast and resolution. In addition the light intensity passed by the optical system is several orders of magnitude greater than the usual high-resolution Rayleigh system so that either exposure times may be reduced to single flashes of 6 μsec on the usual photographic plates or, alternatively, slower emulsions of much higher resolution may be utilized in a practical manner.