Quantitative phase-contrast confocal microscope

Coherent linking between confocal amplitude image and confocal phase image in dual-comb microscopy

We propose a method for integrating confocal amplitude and phase images obtained through dual-comb microscopy (DCM). DCM combines the benefits of confocal laser microscopy and quantitative phase microscopy, offering high axial resolution and scan-less imaging. By leveraging the coherence between confocal amplitude and phase images within the same DCM system, we accurately determine the number of phase wrapping iterations, thereby eliminating ambiguity in phase wrapping. We demonstrate this approach using samples with micrometer-range optical thickness and nanometer-scale surface roughness. The results demonstrate an expanded axial range, spanning from micrometers to millimeters, while maintaining nanometer-level axial resolution. This integrated DCM imaging technique enables the simultaneous acquisition of confocal amplitude image and absolute phase image, thus enhancing its potential for wide-axial-dynamic-range imaging across various applications.

Confocal laser scanning holographic microscopy of buried structures

In this paper, we present a confocal laser scanning holographic microscope for the investigation of buried structures. The multimodal system combines high diffraction limited resolution and high signal-to-noise-ratio with the ability of phase acquisition. The amplitude and phase imaging capabilities of the system are shown on a test target. For the investigation of buried integrated semiconductor structures, we expand our system with an optical beam induced current modality that provides additional structure-sensitive contrast. We demonstrate the performance of the multimodal system by imaging the buried structures of a microcontroller through the silicon backside of its housing in reflection geometry.

Accessible quantitative phase imaging in confocal microscopy with sinusoidal-phase synthetic optical holography

We present a technically simple implementation of quantitative phase imaging in confocal microscopy based on synthetic optical holography with sinusoidal-phase reference waves. Using a Mirau interference objective and low-amplitude vertical sample vibration with a piezo-controlled stage, we record synthetic holograms on commercial confocal microscopes (Nikon, model: A1R; Zeiss: model: LSM-880), from which quantitative phase images are reconstructed. We demonstrate our technique by stain-free imaging of cervical (HeLa) and ovarian (ES-2) cancer cells and stem cell (mHAT9a) samples. Our technique has the potential to extend fluorescence imaging applications in confocal microscopy by providing label-free cell finding, monitoring cell morphology, as well as non-perturbing long-time observation of live cells based on quantitative phase contrast.

Digital adaptive optics confocal microscopy based on iterative retrieval of optical aberration from a guidestar hologram

Guidestar hologram based digital adaptive optics (DAO) is one recently emerging active imaging modality. It records each complex distorted line field reflected or scattered from the sample by an off-axis digital hologram, measures the optical aberration from a separate off-axis digital guidestar hologram, and removes the optical aberration from the distorted line fields by numerical processing. In previously demonstrated DAO systems, the optical aberration was directly retrieved from the guidestar hologram by taking its Fourier transform and extracting the phase term. For the direct retrieval method (DRM), when the sample is not coincident with the guidestar focal plane, the accuracy of the optical aberration retrieved by DRM undergoes a fast decay, leading to quality deterioration of corrected images. To tackle this problem, we explore here an image metrics-based iterative method (MIM) to retrieve the optical aberration from the guidestar hologram. Using an aberrated objective lens and scattering samples, we demonstrate that MIM can improve the accuracy of the retrieved aberrations from both focused and defocused guidestar holograms, compared to DRM, to improve the robustness of the DAO.

Coherent artifact suppression in line-field reflection confocal microscopy using a low spatial coherence light source

Line-field reflection confocal microscopy (LF-RCM) has the potential to add a dimension of parallelization to traditional confocal microscopy while reducing the need for two-axis beam scanning. LF-RCM systems often employ light sources with a high degree of spatial coherence. This high degree of spatial coherence potentially leads to unwanted coherent artifact in the setting of nontrivial sample scattering. Here, we (a) confirm that a coherent artifact is a nontrivial problem in LF-RCM when using spatially coherent light, and (b) demonstrate that such a coherent artifact can be mitigated through the use of reduced spatial coherence line-field sources. We demonstrate coherent noise suppression in a full-pupil line-field confocal microscope using a large number of mutually incoherent emitters from a vertical-cavity surface-emitting lasers (VCSEL) array. The coherent noise from a highly scattering sample is significantly suppressed by the use of this synthesized reduced spatial coherence light source compared to a fully coherent light source. Lastly, with scattering samples, the axial confocality of line-field confocal microscopy is compromised independent of the source spatial coherence, as demonstrated by our experimental result. Our results highlight the importance of spatial coherence engineering in parallelized reflection confocal microscopy.

Three-Dimensional Imaging by Self-Reference Single-Channel Digital Incoherent Holography

Digital holography offers a reliable and fast method to image a three-dimensional scene from a single perspective. This article reviews recent developments of self-reference single-channel incoherent hologram recorders. Hologram recorders in which both interfering beams, commonly referred to as the signal and the reference beams, originate from the same observed objects are considered as self-reference systems. Moreover, the hologram recorders reviewed herein are configured in a setup of a single channel interferometer. This unique configuration is achieved through the use of one or more spatial light modulators.

High-speed line-field confocal holographic microscope for quantitative phase imaging

We present a high-speed and phase-sensitive reflectance line-scanning confocal holographic microscope (LCHM). We achieved rapid confocal imaging using a fast line-scan CCD camera and quantitative phase imaging using off-axis digital holography (DH) on a 1D, line-by-line basis in our prototype experiment. Using a 20 kHz line scan rate, we achieved a frame rate of 20 Hz for 512x512 pixels en-face confocal images. We realized coherent holographic detection two different ways. We first present a LCHM using off-axis configuration. By using a microscope objective of a NA 0.65, we achieved axial and lateral resolution of ~3.5 micrometers and ~0.8 micrometers, respectively. We demonstrated surface profile measurement of a phase target at nanometer precision and the digital refocusing of a defocused confocal en-face image. Ultrahigh temporal resolution M mode is demonstrated by measuring the vibration of a PZT-actuated mirror driven by a sine wave at 1 kHz. We then report our experimental work on a LCHM using an in-line configuration. In this in-line LCHM, the coherent detection is enabled by moving the reference arm at a constant speed, thereby introducing a Doppler frequency shift that leads to spatial interference fringes along the scanning direction. Lastly, we present a unified formulation that treats off-axis and in-line LCHM in a unified joint spatiotemporal modulation framework and provide a connection between LCHM and the traditional off-axis DH. The presented high-speed LCHM may find applications in optical metrology and biomedical imaging.

Digital adaptive optics line-scanning confocal imaging system

A digital adaptive optics line-scanning confocal imaging (DAOLCI) system is proposed by applying digital holographic adaptive optics to a digital form of line-scanning confocal imaging system. In DAOLCI, each line scan is recorded by a digital hologram, which allows access to the complex optical field from one slice of the sample through digital holography. This complex optical field contains both the information of one slice of the sample and the optical aberration of the system, thus allowing us to compensate for the effect of the optical aberration, which can be sensed by a complex guide star hologram. After numerical aberration compensation, the corrected optical fields of a sequence of line scans are stitched into the final corrected confocal image. In DAOLCI, a numerical slit is applied to realize the confocality at the sensor end. The width of this slit can be adjusted to control the image contrast and speckle noise for scattering samples. DAOLCI dispenses with the hardware pieces, such as Shack–Hartmann wavefront sensor and deformable mirror, and the closed-loop feedbacks adopted in the conventional adaptive optics confocal imaging system, thus reducing the optomechanical complexity and cost. Numerical simulations and proof-of-principle experiments are presented that demonstrate the feasibility of this idea.