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A laser accelerometer is an accelerometer that uses a laser to measure changes in velocity/direction.
| | This article needs additional citations for verification .(November 2021) |
A laser accelerometer is an accelerometer that uses a laser to measure changes in velocity/direction.
It employs a frame with three orthogonal input axes and multiple proof masses. Each proof mass has a predetermined blanking surface. A flexible beam supports each proof mass. The flexible beam permits movement of the proof mass on its axis. [1]
A laser light source provides a light ray. The laser source is has a transverse field characteristic with a central null intensity region. A mirror transmits a beam of light to a detector. The detector is positioned to be centered on the light ray and responds to the light's intensity to provide an intensity signal. The signal's magnitude is related to the intensity of the light ray.
The proof mass blanking surface is centrally positioned within and normal to the light ray null intensity region to provide increased blanking of the light ray in response to transverse movement of the mass on the input axis.
In response to acceleration in the direction of the input axis, the proof mass deflects the beam and moves the blanking surface in a direction transverse to the light ray to partially blank the light beam. A control responds to the intensity signal to apply a restoring force to restore the proof mass to a central position and provides an output signal proportional to the restoring force.
Accelerometers are added to many devices, including (smart) watches, phones and vehicles of all kinds. Accelerometers oriented vertically function as gravimeters, useful for mining. [2] Other applications include medical diagnostics and satellite measurements for climate change studies. [1]
Basic lasers operate with a frequency range (line width) of some 500 mHz. The range is widened by small temperature changes and vibrations, and by imperfections in the laser cavity. The line width of a specialised scientific laser approaches 1mHz. [2]
An accelerometer was announced that used infrared light to measure the change in distance between two micromirrors in a Fabry–Perot cavity. The proof mass is a single silicon crystal with a mass of 10–20 mg, suspended from the first mirror using flexible 1.5 μm-thick silicon nitride (Si
3N
4) beams. The suspension allows the proof mass to move freely, with nearly ideal translational motion. The second (convace) mirror acts as the fixed reference point. Light of a certain frequency resonates – bounces back and forth – between the two mirrors in the cavity, increasing its intensity, while other frequencies are discarded. Under acceleration, the proof mass displacement relative to the concave mirror changes the intensity of reflected light. The change in intensity is measured by a single-frequency laser that matches the cavity's resonant frequency.The device can sense displacements under 1 femtometre (10–15 m) and detect accelerations as low as 3.2 × 10-8 g (the acceleration due to Earth’s gravity) with uncertainty under 1%. [1]
An accelerometer was announced with a line width of 20 Hz. The SolsTiS accelerometer has a titanium-doped sapphire cavity that is shaped in a way to encourage a narrow line width and to rapidly dissipate waste heat. The device exploits the wave qualities of atoms. The laser is divided into multiple beams. One beam strikes a diffuse rubidium gas refrigerated to around 10−7 K. This temperature is achieved by using Doppler cooling with six beams to slow/cool the atoms. The atoms split into two quantum waves. A second pulse reverses the split, while a third allows them to interfere with each other, creating an interference pattern that reflects acceleration the waves underwent while separated. Another laser pulse detects the interference patterns in the various atoms, which reflects the amount of acceleration. Military-grade laser accelerometers, drift (accumulate errors at the rate of) kilometres a day. The new devices reduce drift to 2 km a month. [2]
A laser is a device that emits light through a process of optical amplification based on the stimulated emission of electromagnetic radiation. The word "laser" is an acronym for "light amplification by stimulated emission of radiation". The first laser was built in 1960 by Theodore H. Maiman at Hughes Research Laboratories, based on theoretical work by Charles Hard Townes and Arthur Leonard Schawlow.
Interferometry is a technique which uses the interference of superimposed waves to extract information. Interferometry typically uses electromagnetic waves and is an important investigative technique in the fields of astronomy, fiber optics, engineering metrology, optical metrology, oceanography, seismology, spectroscopy, quantum mechanics, nuclear and particle physics, plasma physics, remote sensing, biomolecular interactions, surface profiling, microfluidics, mechanical stress/strain measurement, velocimetry, optometry, and making holograms.
Mode locking is a technique in optics by which a laser can be made to produce pulses of light of extremely short duration, on the order of picoseconds (10−12 s) or femtoseconds (10−15 s). A laser operated in this way is sometimes referred to as a femtosecond laser, for example, in modern refractive surgery. The basis of the technique is to induce a fixed phase relationship between the longitudinal modes of the laser's resonant cavity. Constructive interference between these modes can cause the laser light to be produced as a train of pulses. The laser is then said to be "phase-locked" or "mode-locked".
A seismometer is an instrument that responds to ground noises and shaking such as caused by earthquakes, volcanic eruptions, and explosions. They are usually combined with a timing device and a recording device to form a seismograph. The output of such a device—formerly recorded on paper or film, now recorded and processed digitally—is a seismogram. Such data is used to locate and characterize earthquakes, and to study the Earth's internal structure.
An accelerometer is a tool that measures proper acceleration. Proper acceleration is the acceleration of a body in its own instantaneous rest frame; this is different from coordinate acceleration, which is acceleration in a fixed coordinate system. For example, an accelerometer at rest on the surface of the Earth will measure an acceleration due to Earth's gravity, straight upwards of g ≈ 9.81 m/s2. By contrast, accelerometers in free fall will measure zero.
Tunable diode laser absorption spectroscopy is a technique for measuring the concentration of certain species such as methane, water vapor and many more, in a gaseous mixture using tunable diode lasers and laser absorption spectrometry. The advantage of TDLAS over other techniques for concentration measurement is its ability to achieve very low detection limits. Apart from concentration, it is also possible to determine the temperature, pressure, velocity and mass flux of the gas under observation. TDLAS is by far the most common laser based absorption technique for quantitative assessments of species in gas phase.
An optical cavity, resonating cavity or optical resonator is an arrangement of mirrors that forms a standing wave cavity resonator for light waves. Optical cavities are a major component of lasers, surrounding the gain medium and providing feedback of the laser light. They are also used in optical parametric oscillators and some interferometers. Light confined in the cavity reflects multiple times, producing standing waves for certain resonance frequencies. The standing wave patterns produced are called modes; longitudinal modes differ only in frequency while transverse modes differ for different frequencies and have different intensity patterns across the cross-section of the beam.
Kerr-lens mode-locking (KLM) is a method of mode-locking lasers via the nonlinear optical Kerr effect. This method allows the generation of pulses of light with a duration as short as a few femtoseconds.
A gyrotron is a class of high-power linear-beam vacuum tubes which generates millimeter-wave electromagnetic waves by the cyclotron resonance of electrons in a strong magnetic field. Output frequencies range from about 20 to 527 GHz, covering wavelengths from microwave to the edge of the terahertz gap. Typical output powers range from tens of kilowatts to 1–2 megawatts. Gyrotrons can be designed for pulsed or continuous operation. The gyrotron was invented by Soviet scientists at NIRFI, based in Nizhny Novgorod, Russia.
An acousto-optic modulator (AOM), also called a Bragg cell or an acousto-optic deflector (AOD), uses the acousto-optic effect to diffract and shift the frequency of light using sound waves. They are used in lasers for Q-switching, telecommunications for signal modulation, and in spectroscopy for frequency control. A piezoelectric transducer is attached to a material such as glass. An oscillating electric signal drives the transducer to vibrate, which creates sound waves in the material. These can be thought of as moving periodic planes of expansion and compression that change the index of refraction. Incoming light scatters off the resulting periodic index modulation and interference occurs similar to Bragg diffraction. The interaction can be thought of as a three-wave mixing process resulting in Sum-frequency generation or Difference-frequency generation between phonons and photons.
Ultrafast laser spectroscopy is a spectroscopic technique that uses ultrashort pulse lasers for the study of dynamics on extremely short time scales. Different methods are used to examine the dynamics of charge carriers, atoms, and molecules. Many different procedures have been developed spanning different time scales and photon energy ranges; some common methods are listed below.
Ring lasers are composed of two beams of light of the same polarization traveling in opposite directions ("counter-rotating") in a closed loop.
A piezoelectric accelerometer is an accelerometer that employs the piezoelectric effect of certain materials to measure dynamic changes in mechanical variables.
Laser absorption spectrometry (LAS) refers to techniques that use lasers to assess the concentration or amount of a species in gas phase by absorption spectrometry (AS).
A laser projector is a device that projects changing laser beams on a screen to create a moving image for entertainment or professional use. It consists of a housing that contains lasers, mirrors, galvanometer scanners, and other optical components. A laser projector can contain one laser light source for single-color projection or three sources for RGB full color projection.
A particle accelerator is a machine that uses electromagnetic fields to propel charged particles to very high speeds and energies, and to contain them in well-defined beams.
An inertial navigation system (INS) is a navigation device that uses a computer, motion sensors (accelerometers) and rotation sensors (gyroscopes) to continuously calculate by dead reckoning the position, the orientation, and the velocity of a moving object without the need for external references. Often the inertial sensors are supplemented by a barometric altimeter and sometimes by magnetic sensors (magnetometers) and/or speed measuring devices. INSs are used on mobile robots and on vehicles such as ships, aircraft, submarines, guided missiles, and spacecraft. Other terms used to refer to inertial navigation systems or closely related devices include inertial guidance system, inertial instrument, inertial measurement unit (IMU) and many other variations. Older INS systems generally used an inertial platform as their mounting point to the vehicle and the terms are sometimes considered synonymous.
The history of the oscilloscope reaches back to the first recordings of waveforms with a galvanometer coupled to a mechanical drawing system in the second decade of the 19th century. The modern day digital oscilloscope is a consequence of multiple generations of development of the oscillograph, cathode-ray tubes, analog oscilloscopes, and digital electronics.
An optical transistor, also known as an optical switch or a light valve, is a device that switches or amplifies optical signals. Light occurring on an optical transistor’s input changes the intensity of light emitted from the transistor’s output while output power is supplied by an additional optical source. Since the input signal intensity may be weaker than that of the source, an optical transistor amplifies the optical signal. The device is the optical analog of the electronic transistor that forms the basis of modern electronic devices. Optical transistors provide a means to control light using only light and has applications in optical computing and fiber-optic communication networks. Such technology has the potential to exceed the speed of electronics, while conserving more power.
An acousto-optic programmable dispersive filter (AOPDF) is a special type of collinear-beam acousto-optic modulator capable of shaping spectral phase and amplitude of ultrashort laser pulses. AOPDF was invented by Pierre Tournois. Typically, quartz crystals are used for the fabrication of the AOPDFs operating in the UV spectral domain, paratellurite crystals are used in the visible and the NIR and calomel in the MIR (3-20 µm). Recently introduced Lithium niobate crystals allow for high-repetition rate operation owing to their high acoustic velocity. The AOPDF is also used for the active control of the carrier-envelope phase of the few-cycle optical pulses and as a part of pulse-measurement schemes. Although sharing a lot in principle of operation with an acousto-optic tunable filter, the AOPDF should not be confused with it, since in the former the tunable parameter is the transfer function and in the latter it is the impulse response