High order axially symmetric polarized beams (ASPBs) can create multiple focused spots under tight focusing conditions, and thus have been highly recommended for optical manipulation, but the feasible experiments have never been demonstrated. Cells trapping and manipulation based on optical tweezers using high order ASPBs are presented theoretically and experimentally to verify its feasibility and effectiveness. The focused intensities and corresponding gradient forces for high order ASPBs are first analyzed and calculated if two kinds of particles are trapped respectively based on the electromagnetic theory. Then an optical tweezers based on an inverted microscopy using high order ASPBs is built up, and the yeast cells (~10μm) are trapped and manipulated to shift and rotate using two kinds of ASPBs with P=1 and P=3. One yeast cell is stably trapped and shifted with a speed about 40μm/s and four yeast cells are trapped and rotated simultaneously with a rotation speed about 45°/s, which can also be further modulated and the track of the focusing spot can be programmed by computer. Finally, the optical trap stiffnesses are calculated theoretically using the Boltzmann statistics method and further measured experimentally when the filling factors of the objective lens are 0.50, 0.80 and 1.00 respectively and three microcopy objective lenses with numerical apertures 0.40, 0.65 and 0.85 are used, and the measured results agree well with the calculated results, which shows the trapping performances can be flexibly modulated by setting the system parameters and provides some novel choices for optical manipulations. All these findings benefit the expansion of the practical applications of vector beam OTs in some fields, especially in the field of biomedicine.
We demonstrate a Q-switched mode-locked Er-doped fiber laser using an all-fiber grade-index multimode fiber-based modulator which generates dark-bright pair between bright pulse sequences and alternate bright and dark pulses. A section of dispersion compensation fiber (Nufern UHNA4) considered as a candidate normal group victory dispersion fiber is used to adjust the net dispersion of cavity. At a pump power of 410 mW, evident Q-switched instability modulating mode-locked bright pulses are observed, and the duration of Q-switched envelope changes from 1.8 μs to 8 μs along with the variation of power. Changing the state of polarization controller, the mode-locked bright pulse train is tuned to dark pulse train with reducing the duration of Q-switched envelope to 1.2 μs. What’s more, dark-bright pair between bright pulses train and alternate bright and dark pulses are also observed under second harmonic operations with suitable PC states. Coupled complex Ginzburg-Landau equation, field coupling model for propagation in multimode fiber, and fiber nonlinear effects are provided to reveal the underlying principles of the transition of these pulse trains. Because of the principal modes and filtering effect in multimode fibers, the formation and stable propagation of the dark-bright pair are precisely achieved. At the same time, the physical mechanism behind the unusual pairing of dark and bright pulses is that under certain conditions, cross-phase modulation can counteract the time extension of optical pulses caused by the combination of self-phase modulation and normal dispersion. Thus, the cross-phase modulation induced chirping on dark solitons enables dark-bright pair between bright pulse sequences to coexist.
A single-cavity triple-comb all-fiber laser is proposed by wavelength/polarization multiplexing. A variable optical attenuator is introduced to equalize the 1530-nm and 1550-nm gain profile of erbium-doped fiber for dual-wavelength pulses. Their repetition rate difference reach kHz level. Meanwhile, by further adjusting the intracavity polarization state, polarization-multiplexed dual-comb pulses with tens-of-Hz repetition rate difference in the 1550-nm gain region are obtained. The more than one-order-of-magnitude difference between the maximum and minimum repetition frequency difference and qualified passive mutual coherence of triple-frequency pulses is highlighted. These results indicate a highly potential triple-comb source for multiple-comb metrology such as triple-comb ranging and frequency measurement and so on.
In line structured light vision measurement, due to the occlusion of the object, the complete information might not be collected. We propose a method to acquire the object’s all point data by dual-camera cooperative measurement. First, the transformation models between cameras and motion coordinates are constructed. Subsequently, the light plane is calibrated by special points from the images of the calibration plate which is raised 3 times with an appointed distance. Finally, the data points are fused and optimized with particular matrix. The results show that the average fusion error is reduced from 0.5668 mm to 0.1253 mm. This method improves the reconstruction accuracy greatly.
Multi-species blood identification is especially useful in animal quarantine, import and export, criminal cases, forensic examination, and wildlife conservation. Raman spectroscopy is a non-destructive, label-free, and highly specific method for providing chemical information on materials and serving as an analytical tool to characterize biological samples. Machine learning approaches in conjunction with Raman tweezers are proposed to extract the Raman spectral characteristics of single red blood cells (RBCs), then the cells based on the spectral characteristics are classified, and some classification prediction models to achieve single cell identification of different blood species are achieved finally.
During the caries treatment, three-dimensional measurement of tooth profile and caries location is one of key steps in the therapeutic process of caries. We propose a three-dimensional vision measurement of tooth crown and dental caries with line structured light. First, an integrated calibration using right angled spot target is executed and the parameters are obtained rapidly. Subsequently, the profile of the tooth crown is reconstructed and the dental caries area is identified. The results show that the reprojection error could reach tens of micrometers and the caries’ area is measured as ~ 2.83 mm2. These results indicate high potential in the diagnosis and treatment of dental caries.
We experimentally demonstrate a simple, effective and intelligent scheme to obtain image monitoring of femtosecond laser processing of biological hard tissues. A simple mobile phone camera is adopted for imaging of different processing status of biological hard tissue. Subsequently, an automatic recognition method based deep learning is proposed to recognize the relationship between the optical images and manufacturing effect for the fast parameter optimization of laser processing. Correspondingly, the laser processing parameter could be well controlled to obtain qualified laser processing of biological hard tissue. These results indicate an efficient and accurate image monitoring route for intelligent femtosecond laser processing of biological
Multiple myeloma may develop resistance to certain drugs during chemotherapy, which have a fatal impact on treatment efficacy. At present, the drug resistance detection methods for multiple myeloma, such as proteomic identification and clone formation analysis, are relatively complex, and the accuracy and detection time are not ideal. In our work, laser tweezers Raman spectroscopy was used to collect 412 groups of spectra of two kinds of cells, namely, MM.1R and MM.1S, which were respectively resistant to dexamethasone and sensitive to dexamethasone. We selected support vector machine, random forest, linear discriminant analysis and other algorithms to train the pretreated Raman spectra, and the recognition accuracy on the test set was above 95%. This result shows that the combination of laser tweezers Raman spectroscopy and artificial intelligence algorithm can quickly detect drug resistance of cancer cells.
In this work, we demonstrate a single-walled carbon nanotubes-based wavelength multiplexed fiber laser, which generates dual-comb pulse in the train of soliton rain. The fiber laser cavity is manipulated in repetition frequency of 16.58 MHz, 3 dB spectral bandwidth of 8.4 nm. Two asynchronous pulses constitute the soliton rain pulse sequences, which the intensity difference is about 5.72 dB between the dual frequencies. A piece of graded-index multi-mode fiber as a filter based on the multi-mode interference effect is introduced into cavity to improving the signal to noise ratio to ~62 dB, and locate the central wavelength of the dual-comb at 1556.7 nm and 1561.5 nm. The repetition rate difference of the dual-frequency is about 169 Hz with the resolution bandwidth of 1 Hz. The time delay of the dual-frequency pulse detected by cross-correlation method is 5.78 ms, which is well matched with the results in radio frequency spectrum. Different from the stable period of the general cross-correlation signal, our experimental results show several different sub-periods due to the existence of the drifting solitons in the soliton rain sequences. Meanwhile, the number of different sub-periods in the correlation decreases from six to three as the pump power reduced from 100 mA to 97.3 mA. Our work provides a new sight into the quasi-steady multi-soliton dynamics process in fiber lasers, and will be promising solutions for interference ranging, and synchronization and timing.
In our work, we experimentally demonstrate wavelength multiplexed dual-comb pulses based on multi-modal interference effect in a passively single-walled carbon nanotube mode-locking all fiber ring laser. The laser cavity achieves a variety of dual-wavelength mode-locked states by switching the polarization controller in the laser cavity. A piece of 25 cm long graded-index multi-mode fiber as a filter based on the multi-mode interference effect is introduced into cavity to fixing wavelength and to improving the signal to noise ratio. With optimized length of multi-mode fiber, we observed the two different filter state which located at 1559 nm and 1562 nm, 1561 nm and 1563 nm respectively in the different polarization dual-comb states. With suitable filtering state by stretching the multi-mode fiber, the two asynchronous pulse sequences coexist with diverse operation, which propagate with singlet and double pulses, respectively. The repetition rate of the laser is 16.59 MHz and the time period corresponding to the asynchronous pulse is ~60 ns. The repetition rate difference of dual-wavelength states reaches 100 Hz. In addition, we recorded the output modulation state of the laser cavity. Our research provides experimental basis for optical fiber sensing, wavelength division multiplexing communication system and high resolution spectroscopy.
Due to the simple configuration, qualified passive coherence between pulses, and cost-effective characteristics, single-cavity dual-comb sources attract increasing research interest. Actually, such lasers have been experimentally verified in dual-comb metrology such as dual-comb frequency measurement and spectroscopy. Unlike the single-cavity dual-comb fiber laser multiplexed in other dimensions such as wavelength, direction and mode-locked mechanism, polarization-multiplexed pulses own the unique characteristics of overlapping spectra, intrinsic spectral coherence, and tunable repetition rate difference. They are beneficial for the simplification of additional optical amplification and the satisfaction of versatile requirements of dual-comb metrology. Here, we demonstrated a single-wall carbon nanotube saturable absorber mode-locked Er-doped fiber laser to emit wavelength-switchable polarization-multiplexed dual-comb pulses. The intracavity loss is carefully tuned by an additional optical variable attenuator to define the oscillation windows. In both the 1530- and 1550-nm gain regions, spectral-overlapping, polarization-multiplexed pulses are experimentally obtained with the fine configuration of the intracavity state of polarization. The polarization dynamics and tunable repetition rate difference are experimentally revealed. The repetition rate difference is at the tens-of-hertz level, which is somewhat lower than that of the reported polarization-multiplexed fiber laser with additionally introduced polarization-maintaining fiber. Since there are no additional birefringent media, the polarization mode dispersion for polarization-multiplexed pulses is attributed to the residual birefringence. Moreover, the passive mutual coherence is also highlighted. There results provide a simple yet effective way to design switchable and versatile single-cavity dual-comb pulses.
Raman spectroscopy, a “fingerprint” spectrum of substances, can be used to characterize various biological and chemical samples. To allow for blood classification using single-cell Raman spectroscopy, several machine learning algorithms were implemented and compared. A single-cell laser optical tweezer Raman spectroscopy system was established to obtain the Raman spectra of red blood cells. The Boruta algorithm extracted the spectral feature frequency shift, reduced the spectral dimension, and determined the essential features that affect classification. Next, seven machine learning classification models and deep learning model without dimensionality reduction are analyzed and compared based on the classification accuracy, precision, and recall indicators. The results show that support vector machines and convolutional neural network are the two most appropriate machine learning algorithms for single-cell Raman spectrum blood classification, and the findings provide essential guidance for future research studies.
High-quality gold nanospheres (Au NPs) were transferred to a sapphire substrate. The balanced twin-detector measurement technique was used to study the saturable absorption properties of the Au NPs. With the as-prepared Au NPs as a saturable absorber (SA), an efficient passively Q-switched laser was realized at 1.93 μm. Under an absorbed pump power of 4.5 W, a maximum output power of 400 mW was obtained with the shortest pulse width of 410 ns and repetition rate of 126 kHz. The results indicate that Au NPs are promising candidates as SAs for mid-infrared laser pulse generation.
A method is proposed to suppress speckle noise using only part of the pixels in a single-exposure digital hologram. Different holographic patterns are first generated from a single-exposure digital hologram using specially designed binary masks; then, these holographic patterns are reconstructed according to the Fresnel transform. The reconstructed images are superposed and averaged on the intensity to achieve the suppression of speckle noise. The entire denoising process does not need any additional digital holograms or specific requirements for recording a hologram. Theoretical simulation and experiment verification were carried out and confirm that the proposed method is a very convenient and effective way to suppress speckle noise in digital holography. The proposed method has wide applications in holographic imaging, holographic storage, and art display.
Recently, interferometric null-testing with computer-generated hologram has been proposed as a non-contact and high
precision solution to the freeform optics metrology. However, the interferometry solution owns some typical
disadvantages such as the strong sensitivity to the table vibrations or temperature fluctuations, which hinders its usage
outside the strictly controlled laboratory conditions. Phase retrieval presents a viable alternative to interferometry for
measuring wavefront and can provide a more compact, less expensive, and more stable experimental setup. In this work,
we propose a novel solution to freeform metrology based on phase retrieval and computer-generated hologram (CGH).
The CGH is designed according to the ray tracing method, so as to compensate the aspheric aberration related to the
freeform element. With careful alignment of the CGH and the freeform element in the testing system, several defocused
intensity images can be captured for phase retrieval. In this paper the experimental results related to a freeform surface
with 18×18mm2 rectangular aperture (its peak-to-valley aspherity equals to 193um) are reported, meanwhile, we also
have compared them with the measurement results given by the interferometry solution, so as to evaluate the validity of
our solution.
The aqueous outflow system (AOS) is responsible for maintaining normal intraocular pressure (IOP) in the eye. Structures of the AOS have an active role in regulating IOP in healthy eyes and these structures become abnormal in the eyes with glaucoma. We describe a newly developed system platform to obtain high-resolution images of the AOS structures. By incorporating spectral domain optical coherence tomography (SD-OCT), the platform allows us to systematically control, image, and quantitate the responses of AOS tissue to pressure with a millisecond resolution of pulsed flow. We use SD-OCT to image radial limbal segments from the surface of the trabecular meshwork (TM) with a spatial resolution of ∼5 μm in ex vivo nonhuman primate eyes. We carefully insert a cannula into Schlemm’s canal (SC) to control both pressures and flow rates. The experimental results demonstrate the capability of the platform to visualize the unprecedented details of AOS tissue components comparable to that delivered by scanning electron microscopy, as well as to delineate the complex pressure-dependent relationships among the TM, structures within the SC, and collector channel ostia. The described technique provides a new means to characterize the anatomic and pressure-dependent relationships of SC structures, particularly the active motion of collagenous elements at collector channel ostia; such relationships have not previously been amenable to study. Experimental findings suggest that continuing improvements in the OCT imaging of the AOS may provide both insights into the glaucoma enigma and improvements in its management.
Optical tweezers based on cylindrical vector beams are studied theoretically and experimentally. First, we present the basic concept of a cylindrical vector beam (CVB), whose polarization is axially symmetric to the optical axis. Second, two theoretical modes to analyze the interaction between the light beam and the particle are introduced, respectively, and some simulations have been shown. Then, the system structure and its operation principle are introduced in details, where a spatial light modulator (SLM) is used to flexibly generate the CVBs, and experimental results are also demonstrated, which show some advantages for optical manipulation of particles using CVBs.
With the aim to get harmonic distortion characteristics and frequency components of modulated output signals of a Mach-Zehnder (MZ) intensity modulator, this paper analyzes the optical intensity modulation transfer function by Tailor expandsion method according with the working principle of modulator. From the viewpoint of spectrum, the output signal is mainly comprised of the fundamental harmonic, the second intermodulation harmonic and the third intermodulation harmonic of the input signal and their magnitudes are connected with the bias voltage and Eigen-phase of MZ modulator. The second harmonic distortion and the fundamental harmonic of the modulated output signal are closely related with the drift of the best bias point. When the modulator works at the best DC bias voltage point, the modulated output signals have the minimum second harmonic distortion. If the best bias point drifts, the second harmonic distortion increases and the fundamental harmonic decreases, which changes in proportion to the sine or cosine of the drift voltage. A 1GHz sine signal with 1V amplitude imposed on the modulator, the simulation results by MATLAB presents that the waveform starts distorting along with the drifting of the best bias voltage, which the fundamental wave component starts decreasing and the second harmonic component starts increasing. While at last the fundamental wave component is zero, the frequency of output modulated signal doubles as much the frequency of input signal.
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