Laser Heterodyne Interferometry Research Articles

Effect of healed tympanic membrane perforations on umbo velocity in the rat.

Heterodyne laser interferometry was used to measure tympanic membrane (TM) velocity at the umbo during acoustic stimulation in 2 groups of rats. The control group had a normal TM, while in the other group the TM was perforated and then allowed to heal for at least 28 days. Umbo velocity functions for constant sound pressure level stimuli were obtained for test tones between 0.3 and 40.0 kHz in each animal. The results revealed that velocity was the same in the control and healed TMs below 3.0 kHz. Above 5.0 kHz, the velocity response in the healed ear was between 3 and 12 dB smaller than in the control ears. Histologic evaluation of the healed perforation revealed a thick fibrous reaction between the epidermal and lamina propria layers. The results indicated that the added mass of the scar tissue changed the middle- and high-frequency TM responses.

ヘテロダイン干渉法による動的変位量の測定

Dynamic measurements in the order of nanometer by heterodyne laser interferometry for large displacement! comparing them to the unitscale were studied. Two Wollaston prisms were positioned in the back to back arrangement to expand measurable displacements. Frequency dividers were used to enhance the frequency characteristics of the method effectively. Phase unwrapping which is needed in the phase-shift measurements was carried out by using a personal computer and a kind of package software together with our own. The best figure in the present stage is 70 μm in dynamic range, and 100Hz in frequency range respectively. The method was tested in stochastics and results showed the conservative value of coefficient of variable was 1.0%.

Mechanical response characteristics of the hearing organ in the low-frequency regions of the cochlea.

1. With the use of an in vitro preparation of the guinea pig temporal bone, in which the apical turns of the cochlea are exposed, the mechanical and electrical responses of the cochlea in the low-frequency regions were studied during sound stimulation. 2. The mechanical characteristics were investigated in the fourth and third turns of the cochlea with the use of laser heterodyne interferometry, which allows the vibratory responses of both sensory and supporting cells to be recorded. The electrical responses, which can be maintained for several hours, were recorded only in the most apical turn. 3. In the most apical turn, the frequency locations and shapes of the mechanical and electrical responses were very similar. 4. The shapes of the tuning curves and the spatial locations of the frequency maxima in the temporal bone preparation compared very favorably with published results from in vivo recordings of hair cell receptor potentials and sound-induced vibrations of the Reissner's membrane. 5. Compressive nonlinearities were present in both the mechanical and the electrical responses at moderate sound pressure levels. 6. The mechanical tuning changed along the length of the cochlea, the center frequencies in the fourth and third turns being approximately 280 and 570 Hz, respectively. 7. The mechanical responses of sensory and supporting cells were almost identical in shape but differed significantly in amplitude radially across the reticular lamina.

Acoustically induced vibrations of the Reissner's membrane in the guinea-pig inner ear.

In the inner ear, the Reissner's membrane separates the scala vestibuli from the scala media and is thus of importance for maintaining a positive endocochlear potential. The motion of the membrane is thought to be driven by the vibrations of the underlying hearing organ caused by a hydromechanical coupling between the structures. Since the Reissner's membrane is relatively easily accessible in the cochlea its vibratory response has been used as a measure of the micromechanical behaviour of the hearing organ. To determine whether this indirect measure revealed the true characteristics of the hearing organ, experiments were performed using laser heterodyne interferometry in an in vitro preparation of the guinea-pig temporal bone. Interferometric measurements at the Reissner's membrane and at the surface of the hearing organ directly beneath made it possible to compare the mechanical tuning characteristics of both structures. It was found that the mechanical response characteristics of the Reissner's membrane differed considerably from the hearing organ. The tuning frequency was different and only minor changes in the maximal vibration amplitude were seen when measuring at different radial locations. However, the shape of the response curve changes with location. The Reissner's membrane response appeared to be affected by the mechanical vibrations originating both at the middle ear ossicles and at the hearing organ. It is concluded that the Reissner's membrane response is a poor indicator of cochlear mechanics and that investigations of cochlear micromechanics should be performed directly at the level of the hearing organ.

The vibration pattern of the hearing organ in the waltzing guinea-pig measured using laser heterodyne interferometry

The mechanical tuning characteristics of the hearing organ were measured in response to sound stimulation using laser heterodyne interferometry in in vitro preparations of temporal bones from waltzing guinea-pigs expressing different degrees of hearing organ and sensory cell degeneration. Measurements were made at various stages of structural changes allowing us to correlate structure and mechanical function. It was found that the characteristic frequency of the response at a given location in the cochlea occurred at lower frequencies than what is normally seen and that the sharpness of the mechanical tuning was considerably reduced when sensory hair cells were absent and the hearing organ structurally altered. However, even when extensive hair cell degeneration was evident a residual mechanical tuning was present. These results further support the concept that the sensory hair cells plays a key role in determining normal auditory tuning characteristics. It is suggested that the basilar membrane mechanics gives rise to a broadly tuned mechanical response on which a sharper tuning mechanism, originating from the hair cells, is superimposed.

Shearing motion in the hearing organ measured by confocal laser heterodyne interferometry.

To investigate the presence of the postulated shearing motion in the micromechanics of the inner ear during sound stimulations we measured the vibratory response of the tectorial membrane and the reticular lamina in the third cochlear turn in an isolated temporal bone preparation using confocal laser heterodyne interferometry. The mechanical response of the tectorial membrane had the same frequency of maxima as the underlying reticular lamina, but was not as sharply tuned. When the two-dimensional motion was calculated from measurements made from several viewing angles it was found that the vibration of the reticular lamina had significant components both normal and tangential to its surface. The tectorial membrane motion, however, was primarily in a direction approximately perpendicular to the surface of the reticular lamina. The results indicate that shearing motion is produced predominantly by the radial motion of the reticular lamina.

Shearing motion in the hearing organ measured by confocal laser heterodyne interferometry

To investigate the presence of the postulated shearing motion in the micromechanics of the inner ear during sound stimulation we measured the vibratory response of the tectorial membrane and the reticular lamina in the third cochlear turn in an isolated temporal bone preparation using confocal laser heterodyne interferometry. The mechanical response of the tectorial membrane had the same frequency of maxima as the underlying reticular lamina, but was not as sharply tuned. When the twodimensional motion was calculated from measurements made from several viewing angles it was found that the vibration of the reticular lamina had significant components both normal and tangential to its surface. The tectorial membrane motion, however, was primarily in a direction approximately perpendicular to the surface of the reticular lamina. The results indicate that shearing motion is produced predominantly by the radial motion of the reticular lamina.

Importance of rotational beam alignment in the generation of second harmonic errors in laser heterodyne interferometry

We show, using a Jones matrix analysis, that rotating the two orthogonal linearly polarized inputs of a heterodyne interferometer relative to the polarizing beam splitter axes, produces second harmonic errors in an otherwise ideal interferometer. The error undergoes two cycles as the optical pathlength difference changes from 0 to 2pi. This behaviour is distinct from previously reported periodic errors resulting from polarization leakage and frequency mixing. It is found that as the angular misalignment increases, the amplitude of the periodic errors also increases, and may reach substantial values.

Mechanical tuning characteristics of the hearing organ measured at the sensory cells in the gerbil temporal bone preparation.

The micromechanical behaviour of the inner ear in response to sound stimulation was investigated in an in vitro preparation of the gerbil temporal bone. Using laser heterodyne interferometry it was possible to measure the vibration responses directly at the level of the sensory and supporting cells within the hearing organ rather than from the underlying basilar membrane as has been done in previous studies. There was a tuned mechanical response of the cellular structures within the hearing organ. The resonance frequency measured at cells in the apical (third) turn was around 200Hz. The frequency of the mechanical tuning varied along the length of the cochlea. In the second turn the resonance frequency was around 500-700Hz. The cellular response in the second turn was more sharply tuned as compared to the response in the apical turn. In both cochlear turns the amplitude of the vibratory response changed with the cellular location radially across the hearing organ.

Changes in the Mechanical Tuning Characteristics of the Hearing Organ Following Acoustic Overstimulation

An in vitro preparation of the guinea-pig temporal bone was used to study the effects of acoustic overstimulation on the mechanical tuning characteristics of the inner ear. Using laser heterodyne interferometry, the vibratory responses of selected sensory and supporting cells within the hearing organ were measured in response to acoustic signals applied to the ear to obtain mechanical tuning curves before and after applying acoustic overstimulation. Following overstimulation the frequency at which the maximal vibration response occurred moved towards lower frequencies, the vibration amplitude generally increased and the shape of the mechanical tuning curves became considerably flatter. These effects were seen within minutes of overstimulation. The micromechanical changes were accompanied by distinct morphological changes mainly affecting the first row of outer hair cells, which were swollen and shortened. Hensen bodies and swelling of the subsurface cisternae were observed in the affected cells. Apart from this, most of the shortened cells looked structurally intact, had undamaged sensory hair bundles and made synaptic contacts to both afferent and efferent nerve fibres. The results demonstrate that the outer hair cells play a key role in determining the tuning of the hearing organ.

Mechanics of Contacts at Less than 100Å Scale: Indentation and AFM

ABSTRACTUnderstanding of both low load Nanoindentation and Atomic Force Microscopy relies on a knowledge of the mechanical response of contacts at the few nanometre scale. To investigate this area we have developed a new type of AFM/Indenter which applies forces (<1nN up to 1mN) to a tip mounted on a cantilever. The displacement of the cantilever is detected using laser heterodyne interferometry. The combination gives a direct measurement of contact compliance at very low loads. Contacts of diameter below 100Å can be repeatably made.We show that a water film is generally present in the contact during operation in air, and show how its size can be estimated from our data. One implication is that ambient operation of AFM in both repulsive and attractive modes may necessitate the presence of a liquid lubricating film, explaining the relative lack of damage in many AFM measurements. The estimation of contact area from stiffness is complicated by this layer. We show that the contact stresses are likely to be very high.

Accurate measurement of refractive index of gases using a laser interferometer

Refractive index measurements of air and pure gases have been carried out by using laser heterodyne interferometry. Measurement accuracy better than a few parts into 107 for refractive index of gases, is reported. This is a factor 10 better than the results cited in the literature.

Precision displacement measurement by active laser heterodyne interferometry

We demonstrate an active laser heterodyne interferometer which can automatically compensate environmental disturbances and is capable of precision displacement measurement. Two Zeeman He-Ne lasers were employed. Laser II was used as the light source to stabilize the interferometer by using a piezomirror in a feedback loop. The hetereodyne signal of the two lasers was used to directly calibrate mirror displacement, with the wavelength of laser I tuned to compensate change in the interference signal due to displacement only. Separation of the contributions to the interference signal from displacement and external disturbances was accomplished by using polarization optics. This interferometer was used to measure the hysteresis of a piezoelectric transducer (PZT) over a dynamic range of 0.5 microm with a resolution of +/-0.8 nm.

LASER GENERATION AND DETECTION OF ULTRASOUNDS: R&D ACTIVITIES AT ELECTRICITE DE FRANCE - OPUS Project

Our laboratory is involved in the development of non-conventional techniques for the non-destructive evaluation of metallic materials. Our technological and scientific developments in progress include -laser generation of US waves, -laser heterodyne interferometry for contactless detection of US waves. Concerning the inlerferometric contactless detection, we address the major drawback of this technique, the speckle effect due to the coherent scattering. We investigate some new approaches to overcome this problem. The main applications of these combine techniques, that we suggest, are: -on-line materials characterization (e.g. grain size evaluation in steel sheets) -damage measurements to evaluate the material degree of ageing

Accelerometer Calibration by Dynamic Position Measurement Using Heterodyne Laser Interferometry

A new approach to accelerometer calibration is presented which is applicable to frequencies from 1 mHz to above 25 kHz and to amplitudes from 1 nm to above 10 m. Heterodyne laser interferometry is used to measure dynamically the position of the vibrating accelerometer as a function of phase angle through the vibration cycle. Coherent integration is used to improve the length resolution and noise immunity, and a complete description of the vibration is obtained by Fourier analysis of the position measurements. Insensitivity to distortion is achieved by measuring the accelerometer voltage simultaneously in a similar manner and calculating the accelerometer sensitivity from the fundamental length and voltage amplitudes. One implementation of this approach is described and shown to be capable of calibrating accelerometers in the frequency range 5 Hz to 5 kHz with a least uncertainty in amplitude of ±0,01 nm.

Linear interpolation of periodic error in a heterodyne laser interferometer at subnanometer levels (dimension measurement)

Heterodyne laser interferometry and its accuracy at subnanometer levels are discussed. The simplest optical nonpolarization heterodyne interferometer is tested experimentally to understand and reduce fringe distortion. An accuracy of 0.1 nm for the 633-nm He-Ne laser interferometer is achieved.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Isolated Cochlea Preparation for the Study of Cellular Vibrations and Motility

The preparation using the combined techniques of optical sectioning microscopy and laser heterodyne interferometry provides a unique opportunity to study the mechanical interaction between the hair cells and other cells of the organ of Corti

Direct measurement of dilute dye solution quantum yield by photothermal laser heterodyne interferometry

Laser heterodyne measurements have been used to study the nonradiative energy loss of isolated rhodamine 6G molecules in methanol solutions with different potassium iodide quencher concentrations. Simultaneous measurement of both the relative fluorescent intensity and photothermal phase modulation induced by argon ion laser excitation allows absolute determination of both the quantum yield and the fraction of absorbed photo-energy converted to heat. At zero quencher concentration, their values were found to be 98.2% and 12%, respectively.