Laser Beam Alignment Research Articles

Design and characterization of an optical-fiber-coupled laser-induced desorption source for gas-phase dynamics experiments.

Preparation of neutral non-volatile molecules intact in the gas phase for mass spectrometry or chemical dynamics experiments remains a challenge for many classes of molecules. Here, we report the design and characterization of a fiber-coupled laser-based thermal desorption source capable of preparing intact neutral molecules at high molecular densities in the gas phase for use in velocity-map imaging experiments. Within this source, the sample is deposited onto a thin tantalum foil. Irradiation of the foil from the reverse side by a focused laser beam leads to highly localized heating of the sample, resulting in desorption of a plume of molecules into the gas phase. The fiber-coupled design simplifies the alignment of the desorption laser beam, and the ability to rotate the foil relative to the fixed laser beam allows the sample to be continually refreshed under vacuum. We use 118nm photoionization of three test molecules-uracil, adenine, and phenylalanine-to characterize the source and to demonstrate various aspects of its performance. These include the dependence of the velocity-map imaging performance on the size of the interaction region and the dependence of the laser-induced desorption source emission on desorption laser power and heating time. Signal levels recorded in these measurements are comparable to those we typically obtain in similar experiments using a pulsed supersonic molecular beam, and we, therefore, believe that the source has considerable potential for use in a wide range of chemical dynamics and other experiments.

Effect of Slice Thickness Variation on Spatial Resolution of CT-Scan Device Images at the Bali Mandara Hospital Radiology Installation

Aims: Slice thickness variation analysis on spatial resolution on CT-scan images by determining CNR and SNR values, by making ROI on object and background images. ROI size of objects and backgrounds can be observed with several criteria based on the provisions of the ACR program, so that optimization of CT-Scan image quality can be achieved.
 Place and Duration of Study: The Radiology Installation in Bali Mandara Hospital, between 23 March to 20 May 2022.
 Methodology: Data collection begins with preparing the equipment used, namely CT-Scan, head holder, phantom, and computer. After that, the head holder is placed in the middle of the gantry and then the phantom is placed with the guidance of the laser beam (alignment system). Set the axial beam on the vertical line of section 1 and then set the coronal beam on the horizontal line of section 2. After that, setting the type of examination using the adult head protocol and setting the scan parameters to 80 kV, 100 mAs, and slice thicknesses 1, 2, 3, 4, 6, and 8 mm. After the preparation is done then the next exposure to the phantom. Then the research data in the form of phantom images will be seen as a whole to program on the computer monitor. Measurements were made 5 times for each slice thickness. Next is to analyze the CNR of digital phantom image data on a computer. So that it can be determined object ROI, background ROI, object mean, background mean, and standard deviation of the background.
 Results: The results showed that the thicker the Slice Thickness, the higher the CNR and SNR values. The highest CNR value occurred in air medium (13.70) and the lowest occurred in Nylon (0.86). Likewise, the highest SNR value occurred in air medium (13.84) and the lowest in Nylon (0.99). The highest CNR and SNR values ​​occurred in air medium and the lowest occurred in Nylon. 
 Conclusion: Slice Thickness variations affect the spatial resolution of CT-Scan images as indicated by the CNR and SNR values however, the CNR and SNR values ​​are still above 1.0 for adult head examination and above 0.7 for children's head examination. So that the quality of CT-Scan images at Bali Mandara Hospital is still very good.

Method for active spatial alignment and stabilization of laser beams in multi-beam systems

We propose a new method for the development of multi-beam systems for the spatial alignment and stability of beams based on the error separation technique. This method avoids alignment errors caused by coupling effect of piezoelectric devices, inaccurate correction calculations, and detection mode of the angular deviation. According to the results by external detectors, the error value of spatial alignment and the root mean square (RMS) of deviations under control during 1 h can be equivalent to approximately 0.87 and 1.06 nm at the sample plane under an oil immersion lens (focal length f=2 mm). The RMS of deviations is less than one-third of those currently reported for multi-beam systems; therefore, higher alignment and stability accuracy can be achieved with our proposed method.

Pulse Picking PIV: A Single-Cavity Fiber Laser System For Highly Flexible Repetition Rates And Pulsing Schemes

A novel single-cavity laser system with flexible pulsing schemes suitable for particle image velocimetry (PIV) measurements is presented. The system is based on the concept of picking selected pulse pairs from an ultra-high repetition rate fiber laser which enables time-resolved and conventional dual-pulse PIV at highly flexible recording frame rates. Pulse picking PIV laser systems allow for the use of high-quality low speed dual-frame PIV cameras as well as highspeed cameras in both dual-frame and continuous recording modes, enabling the investigation of highly-transient phenomena at limited fields of view using time-resolved PIV as well as statistical PIV measurements with larger fields of view and higher spatial resolutions. The single-cavity output additionally avoids the alignment of laser beams of laser pulses, which is otherwise necessary in conventional dual-cavity PIV laser systems. Two pulse picking systems were set up and tested: An acousto-optic deflector selecting pulses using the diffraction across an acoustic wave and an electro-optic modulator rotating the polarization state of selected pulses in a Pockels cell. The performance of both systems was evaluated in terms of achievable inter-pulse durations, beam profile alterations, and pulse energy losses caused by the introduction of additional optical elements in the beam path.

Challenges in double-beam laser interferometry measurements of fully released piezoelectric films

When utilizing double-beam laser interferometry to assess the piezoelectric coefficient of a film on a substrate, probing both top and bottom sample surfaces is expected to correct the erroneous bending contribution by canceling the additional path length from the sample height change. However, when the bending deformation becomes extensive and uncontrolled, as in the case of membranes or fully released piezoelectric films, the double-beam setup can no longer account for the artifacts, thus resulting in inflated film displacement data and implausibly large piezoelectric coefficient values. This work serves to identify these challenges by demonstrating d33,f measurements of fully released PZT films using a commercial double-beam laser interferometer. For a 1 μm thick randomly oriented PZT film on a 10 μm thick polyimide substrate, a large apparent d33,f of 9500 pm/V was measured. The source of error was presumably a distorted interference pattern due to the erroneous phase shift of the measurement laser beam caused by extensive deformation of the released sample structure. This effect has unfortunately been mistaken as enhanced piezoelectric responses by some reports in the literature. Finite element models demonstrate that bending, laser beam alignment, and the offset between the support structure and the electrode under test have a strong influence on the apparent film d33,f.

The Story behind the First Automatic Atomic Force Microscope

Abstract:Over the past three decades, atomic force microscopy (AFM) has undergone a series of design changes to attain a flat XY scan and stable non-contact mode in ambient atmosphere. AFM has evolved into an ideal method for non-destructive scanning of samples with longer probe tip life, high accuracy, repeatability, and automation. Together with self-optimizing algorithms for scan parameters in the non-contact mode, AFM can become as widely adopted as other microscopies such as optical or scanning electron microscopy (SEM). Even full automation of AFM probe tip exchange is now possible with probe type recognition software and laser beam alignment on the cantilever and position-sensitive photo diode (PSPD). By separating the optics stage from the Z stage, an AFM system can be made with low mechanical noise and improved optical vision.

New Generation Free-Space Optical Communication Systems With Advanced Optical Beam Stabilizer

In this paper, we introduce a novel concept and design of a full-duplex and all-optical FSO transceiver and evaluate its transmission performance in 200 m outdoor environment. Our transceiver enables a reliable fiber-to-fiber FSO link with intelligent lens-based optical-beam-stabilization (OBS) by utilizing miniaturized and cost-effective 3-axis voice-coil motors (VCMs) actuators. The VCM-based moving lens that is widely used in smartphone cameras for auto-focus and optical-image-stabilization is customized and optimized for our designed transceiver to expand the transmitter and receiver field-of-view, control both the transmitted and incident laser beam alignment, suppress the effects of random beam angle-of-arrival fluctuations induced by the atmospheric turbulence and pointing errors and maintain efficient direct coupling to the fiber core at the receiver. Unlike the 2-axis fast-steering-mirrors, the use of 3-axis VCM lenses can not only maintain the beam alignment, but also control the beam collimation and adjust the difference between the lens focal plane and projection plane for a higher fiber coupling efficiency. Using our developed FSO transceivers, we demonstrate an error-free transmission of the standard signals 10 GbE LAN and common public radio interface (LTE-CPRI) over 200 m links. We also performed a continuous 24-h transmission evaluation in a clear weather day, with only occasional burst errors were recorded and a total 24-h BER of 3 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\times 10^{-10}$</tex-math></inline-formula> . The obtained results demonstrate the potential of our proposed FSO transceiver to ensure high-capacity communication links and facilitate the adoption of the FSO system as a viable candidate to address the main requirements of B5G/6G networks.

QEPAS sensor using a radial resonator

We report on the use of a radial acoustic resonator to increase the acoustic signal of a quartz enhanced photoacoustic spectroscopy (QEPAS) sensor. This approach is an attractive alternative to usual configurations based on microtube longitudinal resonators since it enables to substantially relax laser beam alignment and positioning and thus paves the way towards more cost-effective industrial production. This new QEPAS configuration is first investigated and designed by finite element simulation. It is then experimentally implemented and characterised by detecting acetylene around 1.5 µm. The combination of the radial acoustic resonator with a custom quartz tuning fork (QTF) leads to a QEPAS sensor with a normalised noise equivalent absorption (NNEA) of $$3.9 \times 10^{-9}$$ W cm $$^{-1}$$ Hz $$^{-1/2}$$ which is close to the performance of state-of-the-art QEPAS sensors based on microtube resonators.

ICESat‐2 Pointing Calibration and Geolocation Performance

AbstractICESat‐2 science requirements are dependent on the accurate real‐time pointing control (i.e., geolocation control) and postprocessed geolocation knowledge of the laser altimeter surface returns. Prelaunch pointing alignment errors and postlaunch pointing alignment variation result in large geolocation errors that must be calibrated on orbit. In addition, the changing sun‐orbit geometry causes thermal‐mechanical forced laser frame alignment variations at the orbit period and trends from days, weeks, and months. Early mission analysis computed precise postlaunch laser beam alignment calibration. The alignment calibration was uploaded to the spacecraft and enabled the pointing control performance to achieve 4.4 ± 6.0 m, a significant improvement over the 45 m (1 σ) mission requirement. Laser frame alignment calibrations are used to reduce the alignment bias and time variation, as well as the orbital variation contributions to geolocation knowledge error from 6 to 1.7 m (1 σ). Relative beam alignment of the six beams is calibrated and shown to contribute between 0.5 ± 0.1 m and 2.4 ± 0.2 m of remaining geolocation knowledge error. Independent geolocation assessment based on comparison to high‐resolution digital elevation models agrees well with the calibration geolocation error estimates. The analysis demonstrates the ICESat‐2 mission is performing far better than its geolocation knowledge requirement of 6.5 m (1 σ) after the laser frame alignment bias variation and orbital variation calibrations have been applied. Remaining geolocation error is beam dependent and ranges from 2.5 m for beam 6 to 4.4 m for beam 2 (mean + 1 σ).

The Raspberry Pi auto-aligner: Machine learning for automated alignment of laser beams

We present a novel solution to automated beam alignment optimization. This device is based on a Raspberry Pi computer, stepper motors, commercial optomechanics and electronic devices, and the open-source machine learning algorithm M-LOOP. We provide schematic drawings for the custom hardware necessary to operate the device and discuss diagnostic techniques to determine the performance. The beam auto-aligning device has been used to improve the alignment of a laser beam into a single-mode optical fiber from manually optimized fiber alignment, with an iteration time of typically 20minutes. We present example data of one such measurement to illustrate device performance.

A vision system for pose estimation of an underwater robot

This paper presents a vision system designed for an underwater robot to facilitate measuring the distance to an inspected surface and its orientation with respect to the robot. The system uses a set of laser modules to project a rectangular dot pattern on the inspected surface. The vision system is used to measure the dots’ locations in the 3D space and calculate the distance to the surface, together with the pitch angle and the yaw angle of the camera. A novel calibration procedure is presented, which allows for constructing high resolution camera-laser systems, without requiring a perfect alignment of laser beams and camera optical axis. An underwater vision system simulation environment, based on open-source software, is also introduced and extensively used to test the developed algorithms. The experimental results, obtained in a laboratory tank and a pool, confirm high performance of the system.

A new imaging-based method for alignment of multiple laser beams.

A new method for multiple laser beams alignment, useful in a wide range of spectroscopies, is proposed and demonstrated. The method, based on the coupling of spatial map imaging (SMI) with velocity map imaging (VMI), aided beams visualization, through interrogation of the ionization signal of different species in a time-of-flight mass spectrometer. This approach is very effective for alignment and for evaluating the spatial overlap of laser beams with a molecular beam. This was demonstrated by monitoring the resonant two-photon ionization spectrum of 2-phenylethylamine (PEA) monomer and its hydrated (PEA-H2O) cluster and the ionization-loss stimulated Raman spectrum of the cluster, via VMIs accumulation, as a function of the exciting laser wavelength. The former permitted immediate classification of the features in the spectrum, corresponding to the molecular ion or the cluster. The proposed methodology will be useful in other challenging multiple laser beam experiments for spectroscopic studies and is expected to improve extensively their outcome.

A low-noise, high-SNR balanced homodyne detector for the bright squeezed state measurement in 1–100 kHz range**Project supported by the National Natural Science Foundation of China (Grant Nos. 11654002, 61575114, 11874250, and 11804207), the National Key Research and Development Program of China (Grant No. 2016YFA0301401), the Program for Sanjin Scholar of Shanxi Province, China, the Program for Outstanding Innovative Teams of

We report a low-noise, high-signal-to-noise-ratio (SNR) balanced homodyne detector based on the standard transimpedance amplifier circuit and the inductance and capacitance combination for the measurement of the bright squeezed state in the range from 1 kHz to 100 kHz. A capacitance is mounted at the input end of the AC branch to prevent the DC photocurrent from entering the AC branch and avoid AC branch saturation. By adding a switch at the DC branch, the DC branch can be flexibly turned on and off on different occasions. When the switch is on, the DC output provides a monitor signal for laser beam alignment. When the switch is off, the electronic noise of the AC branch is greatly reduced at audio-frequency band due to immunity to the impedance of the DC branch, hence the SNR of the AC branch is significantly improved. As a result, the electronic noise of the AC branch is close to −125 dBm, and the maximum SNR of the AC branch is 48 dB with the incident power of 8 mW in the range from 1 kHz to 100 kHz. The developed photodetector paves a path for measuring the bright squeezed state at audio-frequency band.

Method and apparatus for measuring the stability of large lateral transfer retroreflectors through a single optical port.

Achieving precise alignment between spatially separated optical axes is a challenging problem in optical applications such as boresighting, rangefinding, laser tracking, and optical beam delivery. The Advanced Topographic Laser Altimeter System (ATLAS) developed for NASA's Ice, Cloud and Land Elevation Satellite-II (ICESat-2) mission launched in 2018 was one such application where the alignment of the transmitter laser beam to the receiver telescope is critical for the operation of the instrument. This paper discusses a novel approach for verifying the stability of high-precision beam pointing in the conditions of the Thermal Vacuum (TVAC) test, developed for ATLAS testing at NASA Goddard Space Flight Center. It includes a method and an optical assembly that enables measuring tiny variations in the pointing of the beams of a large lateral transfer retroreflector through a single optical access port such as a TVAC chamber window. The method can be applied for verifying the alignment of optical beams separated by extended distances of tens of meters in vacuum.

Equipment complex and method for aiming laser beams at specified target points

We describe a technique for automatic alignment and targeting of laser beams on a specific point in space using the simulated cubical targets typically used for focusing and targeting of laser light in a multiple beamline laser facility where the target is illuminated in cubical symmetry for high-temperature plasma physics research. We describe the targeting system and the steps for targeting and focusing laser beams at specific points in the target chamber, as well as a method for measuring the length of an arbitrary line segment on a distant object from an image on a display, and an experimental estimate of the accuracy of such measurements on a test object—the edge of the simulated cubical target.

Realization of orthogonality in two-step laser focused Cr atomic deposition

Two-dimensional nano-gratings hold the advantages of good pitch accuracy for nonlinearity calibration and angle accuracy for orthogonality calibration, however, it is very challenging to transfer an ideal orthogonal angle from macroscale to nanoscale. In this study, we utilize a group of perpendicular mirrors in two-step laser focused Cr atomic deposition technology to fabricate a self-traceable two-dimensional nano-gratings. According to theoretical analysis, the novel method will produce an angle uncertainty of around 10″ for the self-traceable array, which helps to realize good orthogonality in the fabrication of a self-traceable two-dimensional nano-grating standard for nanoscale calibration with high accuracy. At the meanwhile, this orthogonality transfer method proposed holds the advantages of highly uniform orthogonal angles over the whole structure area and are insensitive to alignment of laser beams and pitch differences between two step depositions, which opens a new way to transfer an ideal orthogonal or fixed angle from macroscale to nanoscale with high accuracy, uniformity and stability.

Precision Measurement Method of Laser Beams Based on Coordinate Measuring Machine

A high-precision stability measurement scheme was designed and prototyped with the purpose of ensuring precise laser beam alignment during the assembly of an integrated interferometer. With retroreflectors added, the angular resolution of the system is improved while ensuring system stability. Hydroxide-catalysis bonding technology is used to create a stress-free bond between the various optical components of the system. After calibration using the coordinate measuring machine, the device achieved a measurement accuracy of $\pm 6~\mu \text{m}$ for the absolute position of the laser beam in the global coordinate system. In angular measurements, an accuracy of $\pm 21~\mu $ rad was attained. Over a 2-month period, the maximum positional drifts and the maximum angular drifts of the calibration parameters were $\pm 3~\mu \text{m}$ and $\pm 27~\mu $ rad, respectively.

Multipoint vertical-Thomson scattering diagnostic on HL-2A tokamak.

Some progress has been made to develop the multipoint Thomson scattering (TS) diagnostic for the HL-2A tokamak physics experiments. Hardware of silicon avalanche photodiode detector electronics is improved, which provides two output signal channels. In one channel, only the rapid TS signal is the output after deducting the influence of the background slow-varying plasma light. In the other, both the rapid TS signal and the plasma background signal are the output. In the latest HL-2A experiment campaign, the newly developed electronics are tested and TS signals can be obtained from each of the two channels, where the signal is digitized by 12-bit transient recorder sampled at 1 GS/s. Laser beam alignment is fulfilled by using motorized stages to control the laser beam passing through ∼10 mm-wide narrow throats of the lower and upper closed divertors with small movements and then the stray laser light is reduced. New modules of fast digitizers with more than 100 channels are installed and will be used to record TS pulse signals. On the basis of these achievements, about 15-point measurements of plasma electron temperature and density by Thomson scattering diagnostic will come into operation in the upcoming HL-2A experiment campaign.

Surface localisation of laser photoelectron emission using Cu2O and Ag film structures

A laser electron source localised on a photocathode surface was developed on the basis of Ag and Cu2O thin films sequentially deposited by magnetron sputtering on a glass substrate. Photoemission of electrons under the action of the fourth (263 nm) harmonic of a femtosecond fibre laser was initiated from the surface of an Ag film deposited on the substrate surface. Photoelectron source localisation on the photocathode surface was provided by sputtering the Cu2O copper oxide film on its surface, which significantly (about 50 times) reduced the photoemission efficiency, and by subsequent removal of the copper oxide layer in the photoemission spot with a diameter of ∼15 μm by means of focused second-harmonic radiation of a femtosecond fibre laser. In conducting research on the photocathode surface, a grid of photoemission spots was formed, which greatly facilitated the laser beam alignment with the photoemission spot. A decrease in the noises of ultrafast transmission electron microscope, associated with spatial fluctuations of the laser beam initiating pulsed photoelectron emission from the microscope photocathode when using a localised electron source on the basis of a structure of thin Cu2O and Ag films, was experimentally demonstrated.

Flexible and wavelength-independent optical transmission for laser pointing stabilization and assembly error compensation.

A flexible light guide was developed for an ITER (International Thermonuclear Experimental Reactor) poloidal polarimeter which is a passive laser beam alignment and stabilization system for free-space propagation of a wide range of wavelengths. The advantages of using a flexible light guide are (1) to compensate the relative movement between the floor of a building and an optical table, (2) to negate assembly error of the optical transmission line, (3) to minimize the time required for assembly of the line and laser position alignment in a radiological environment, and (4) to transmit a wide wavelength range from visible to far-infrared. The authors fabricated a flexible light guide with an inner diameter of 120 mm and with a motion range of 10 cm. Pointing stability of the laser beam passing through the flexible light guide was less than 70 μrad when the support moved ±50 mm. A flexible light guide error of 70 μrad leads to a beam position displacement of 0.98 mm at a beam position steering mirror ITER poloidal polarimeter that is located 14 m from the flexible light guide. The achieved error is stable enough to guide the laser beam to its target in ITER.