Jeff A Squier

• Colorado School of Mines

Spatial frequency modulation imaging (SPIFI) has previously been demonstrated in multiphoton modalities with resolution enhancement. When signal light levels are low enough, signals consist of discrete pulses: this is a photon-counting regime. By binning photon counts into discrete time bins, SPIFI signals can be built up by incrementing the photon...

Multiphoton, single pixel detection, spatial frequency modulation imaging (SPIFI) is demonstrated in a photon counting regime for the first t ime b y u sing custom multi-threaded software, enabling second harmonic generation (SHG) 4th order enhanced images.

Imaging with spatial frequency modulation for imaging (SPIFI) is pushed to the limits of imaging speed and detection sensitivity. Images are captured with a single 30-fs pulse. Signal sensitivity is improved through photon counting detection.

We demonstrate a throughput increase of third-harmonic generation microscopy imaging using arbitrary illumination patterns. A ‘camera-in-the-loop’ feedback control optimizes the hologram displayed by a spatial light modulator and two different image reconstruction methods are implemented.

Laser Powder Bed Fusion faces imaging challenges due to low numerical aperture optics, fast laser-scanning speeds, and scattering media. Using Spatial Frequency Modulation Imaging, we achieved scatter-robust, enhanced-resolution imaging of melt track formation in-situ.

Spatial frequency modulation imaging (SPIFI) is demonstrated with rapid acquisition, processing, and rendering used in conjunction with a fusing laser system for modifying metallic objects or performing laser powder bed fusion.

Spatial frequency modulation imaging (SPIFI) provides a simple architecture for modulating an extended illumination source that is compatible with single pixel imaging. We demonstrate wavelength domain SPIFI (WD-SPIFI) by encoding time-varying spatial frequencies in the spectral domain that can produce enhanced resolution images, like its spatial d...

Significance Multiphoton microscopy is a powerful imaging tool for biomedical applications. A variety of techniques and respective benefits exist for multiphoton microscopy, but an enhanced resolution is especially desired. Additionally multiphoton microscopy requires ultrafast pulses for excitation, so optimization of the pulse duration at the sam...

Spatial frequency modulation for imaging (SPIFI) has traditionally employed a time-varying spatial modulation of the excitation beam. Here, for the first time to our knowledge, we introduce single-shot SPIFI, where the spatial frequency modulation is imposed across the entire spatial bandwidth of the optical system simultaneously enabling single-sh...

Imaging beyond the diffraction limit barrier has attracted wide attention due to the ability to resolve previously hidden image features. Of the various super-resolution microscopy techniques available, a particularly simple method called saturated excitation microscopy (SAX) requires only simple modification of a laser scanning microscope: The ill...

During the last two decades, ultrafast in-volume laser-based processing of transparent materials has emerged as a key 3D-printing method for manufacturing a variety of complex integrated photonic devices and micro-parts. Yet, identifying suitable laser process parameters for a given substrate remains a tedious, time-consuming task. Using a single l...

Imaging beyond the diffraction limit barrier has attracted wide attention due to the ability to resolve image features that were previously hidden. Of the various super-resolution microscopy techniques available, a particularly simple method called saturated excitation microscopy (SAX) requires only a simple modification of a laser scanning microsc...

Spatial frequency modulation imaging (SPIFI) is a structured illumination single pixel imaging technique that is most often achieved via a rotating modulation disk. This implementation produces line images with exposure times on the order of tens of milliseconds. Here, we present a new architecture for SPIFI using a polygonal scan mirror with the f...

A high-speed super-resolution computational imaging technique is introduced on the basis of classical and quantum correlation functions obtained from photon counts collected from quantum emitters illuminated by spatiotemporally structured illumination. The structured illumination is delocalized—allowing the selective excitation of separate groups o...

Conventional methods for three-dimensional (3D) imaging frequently rely on voxel-by-voxel data acquisition, which restricts the range of specimens in which they can be effectively employed. While advances in imaging technology now permit the routine acquisition of 3D images approaching video rates, there are other limitations to image formation in...

We present the first experimental demonstration of wavelength-multiplexing in single-shot ptychography. Specifically, we experimentally reconstruct the complex transmission profile of a wavelength-independent and wavelength-dependent object simultaneously for 532 nm and 633 nm probing wavelengths. In addition, we discuss the advantages of a more ge...

We present a novel single element detector imaging scheme in which spatial information is encoded into the spectral content of a broadband source. The technique is confocal when delivered with optical fiber.

Glass micromodels have been extensively used to simulate and investigate crude oil, brine, and surface interactions due to their homogeneous wettability, rigidity, and ability to precisely capture a reservoir’s areal heterogeneity. Most micromodels are fabricated via two-dimensional patterning, implying that feature depths are constant despite vary...

We present a scan free extension of SPIFI imaging by wavelength multiplexing. A high-speed spectrometer provides rapid data collection with no beam scanning or frequency swept sources. Results and Images are presented.

Optical diffraction tomography (ODT) is an indispensable tool for studying objects in three dimensions. Until now, ODT has been limited to coherent light because spatial phase information is required to solve the inverse scattering problem. We introduce a method that enables ODT to be applied to imaging incoherent contrast mechanisms such as fluore...

Due to its hardness, strength, and transparency, sapphire is an attractive material for the construction of microfluidic devices intended for high-pressure applications, but its physiochemical properties resist traditional microfabrication and bonding techniques. Here a femtosecond pulsed laser was used to directly machine fluidic channels within s...

Diagnostics capable of interrogating dynamics in harsh environments such as plasma have remained essentially unchanged in recent decades. Developments in advanced microscopy techniques will improve our understanding of the physics involved in these events. Recently developed single-shot ptychography (SSP) provides a pathway towards sophisticated pl...

Pore‐scale mineral dissolution reactions are of fundamental importance for sustaining life and determining the fate of chemicals in Earth's near‐surface environments. However, experimental investigations are largely limited to macroscopic approaches due to difficulties in controlling and observing geochemical processes at the pore scale. Here, we p...

Optical diffraction tomography is an indispensable tool for studying objects in three-dimensions due to its ability to accurately reconstruct scattering objects. Until now this technique has been limited to coherent light because spatial phase information is required to solve the inverse scattering problem. We introduce a method that extends optica...

Spatial frequency modulated imaging (SPIFI) enables the use of an extended excitation source for linear and nonlinear imaging with single element detection. To date, SPIFI has only been used with fixed excitation source geometries. Here, we explore the potential for the SPIFI method when a spatial light modulator (SLM) is used to program the excita...

One of the primary challenges in advanced manufacturing (AM) is the lack of efficient optical metrics for ensuring quality control over the manufacturing process. Many current imaging techniques have excessive data requirements and require computationally intensive post-processing to effectively characterize various AM environments. Spatial frequen...

We present multi-wavelength single-shot ptychography, a technique which is ideally suited for imaging dynamically evolving plasmas. Through improvements to single-shot ptychography and a novel probe constraint, wavelength-multiplexed single-shot ptychography was developed and experimentally realized.

Spatial frequency modulation imaging has a broad range of attributes: enhanced resolution in linear and nonlinear imaging modalities, phase sensitivity, and random access capability. Advanced manufacturing to the neurosciences can benefit from this unique optical metrology.

One of the primary challenges in advanced manufacturing (AM) is the lack of efficient optical metrics for ensuring quality control over the manufacturing process. Many current imaging techniques have excessive data requirements and require computationally intensive post-processing to effectively characterize various AM environments. Spatial frequen...

We introduce a new form of tomographic imaging that is particularly advantageous for a new class of super-resolution optical imaging methods. Our tomographic method, Fourier Computed Tomography (FCT), operates in a conjugate domain relative to conventional computed tomography techniques. FCT is the first optical tomography method that records compl...

The papers in this special section focus on ultrafast science and technology. This field has seen a big highlight, since the Nobel prize in physics for 2018 was announced in high intensity lasers. The application space integrates state-of-the-art photonics techniques coming from the areas of quantum electronics, lasers, fiber optics and electro-opt...

Fluorescence microscopy is a powerful method for producing high fidelity images with high spatial resolution, particularly in the biological sciences. We recently introduced coherent holographic image reconstruction by phase transfer (CHIRPT), a single-pixel imaging method that significantly improves the depth of field in fluorescence microscopy an...

In this Letter, an in-line, compact, and efficient quantitative pulse compensation and measurement scheme is demonstrated. This simple system can be readily deployed in multiphoton imaging systems and advanced manufacturing where multiphoton processes are exploited.

Programmable, two-dimensional, spatial frequency modulation linear and nonlinear imaging combined with a novel and remarkably simple, in-situ quantitative pulse compensation and measurement scheme is demonstrated for the first time.

We introduce a new tomographic imaging technique called Fourier Computed Tomography (FCT). FCT aims to alleviate the anisotropic resolution generated by MP-SPIFI.

Interferometric spatial frequency modulation for imaging (I-SPIFI) is demonstrated for the first time, to our knowledge. Significantly, this imaging modality can be seamlessly combined with nonlinear SPIFI imaging and operates through single-element detection, making it compatible for use in scattering specimens. Imaging dynamic processes with subm...

Analysis of Anorthite Dissolution on the Submicrometer Scale - Volume 24 Supplement - Margariete G. Malenda, Heewon Jung, Jeff Squier, Brian Gorman, Alexis Navarre-Sitchler

With the recent rise of laser additive manufacturing (AM), it has become critical to streamline the process from concept to the finished component. In this paper we demonstrate novel capabilities achieved through post-processing of the laser AM part by femtosecond laser micromachining. For the first time, we show surface roughness values can be red...

We derive analytic expressions for the three-dimensional coherent transfer function (CTF) and coherent spread function (CSF) for coherent holographic image reconstruction by phase transfer (CHIRPT) microscopy with monochromatic and broadband illumination sources. The 3D CSF and CTF were used to simulate CHIRPT images, and the results show excellent...

Spatial frequency modulated imaging (SPIFI) is a powerful imaging method that when used in conjunction with multiphoton contrast mechanisms has the potential to improve the spatial and temporal scales that can be explored within a single nonlinear optical microscope platform. Here we demonstrate, for the first time to our knowledge, that it is poss...

Spatial Frequency Modulated Imaging (SPIFI) with nonlinear excitation is shown to enable super-resolved imaging of specimens via real or virtual state contrast. Extension of 1D enhancement to 2D through inverse domain tomography is discussed.

We show that single-pixel with CHIRPT microscopy encodes optical aberrations in temporal modulations of fluorescent light emitted from a specimen. We recover aberrations from several test objects and remove them digitally after image collection.

For the first time, dynamic phase contrast imaging is demonstrated using single element detection, spatial frequency modulated imaging (SPIFI). Sub-micron axial resolution is shown.

Novel capabilities including surface roughness modification, nanograting formation, and micro-cone generation are achieved through post-processing of additively manufactured (Ti-6Al-4V) parts by a single amplified femtosecond laser. The resulting applications of these surface features are discussed.

Varying microfluidic channel cross-sectional geometry can dramatically alter fluid flow behavior, particularly for capillary-driven flow. Most fabrication techniques, however, are planar and therefore incapable of providing depth-dependent variations in width. We introduce an ultrafast laser ablation technique that enables the fabrication of microc...

Raman spectroscopy is the workhorse for label-free analysis of molecules. It relies on the inelastic scattering of incoming monochromatic light impinging molecules of interest. This effect leads to a very weak emission of light spectrum that provides a signature of the molecules being observed. Considerable efforts have been made over the last deca...

Spatial Frequency Modulated Imaging (SPIFI) with single element detection has previously been demonstrated with a time varying amplitude spatial frequency. SPIFI is capable of providing enhanced resolution images. We present a microscope design which uses a nematic spatial light modulator to provide a time varying amplitude or phase grating. The pe...

Previous work has demonstrated modulated imaging with binary masks. We present a new microscope that provides continuous modulation with a spatial light modulator, which can modulate through multiple methods: amplitude, phase, polarization, etc.

MultiPhoton SPatIal Frequency modulated Imaging (MP-SPIFI) has recently demonstrated the ability to simultaneously obtain super-resolved images in both coherent and incoherent scattering processes — namely, second harmonic generation and two-photon fluorescence, respectively.¹ In our previous analysis, we considered image formation produced by the...

A chirped-pulse amplification system is used to simultaneously image and machine. By combining simultaneous spatial and temporal focusing (SSTF) with spatial frequency modulation for imaging (SPIFI), we are able to decouple the imaging and cutting beams to attain a resolution and a field-of-view that is independent of the cutting beam, while mainta...

Proper alignment is critical to obtain the desired performance from focused spatially chirped beams, for example in simultaneous spatial and temporal focusing (SSTF). We present a simple technique for inspecting the beam paths and focusing conditions for the spectral components of a broadband beam. We spectrally resolve the light transmitted past a...

This study describes a linear optical stretcher as a high-throughput mechanical property cytometer. Custom, inexpensive, and scalable optics image a linear diode bar source into a microfluidic channel, where cells are hydrodynamically focused into the optical stretcher. Upon entering the stretching region, antipodal optical forces generated by the...

We demonstrate pulse shaping via arbitrary phase modulation with a reflective, 1×4096 element, liquid crystal spatial light modulator (SLM). The unique construction of this device provides a very high efficiency when the device is used for phase modulation only in a prism based pulse shaper, namely 85%. We also present a single shot characterizatio...

We demonstrate a spectral interferometric method to characterize lateral and angular spatial chirp to optimize intensity localization in spatio-temporally focused ultrafast beams. Interference between two spatially sheared beams in an interferometer will lead to straight fringes if the wavefronts are curved. To produce reference fringes, we delay o...

Super-resolved far-field microscopy has emerged as a powerful tool for investigating the structure of objects with resolution well below the diffraction limit of light. Nearly all super-resolution imaging techniques reported to date rely on real energy states of probe molecules to circumvent the diffraction limit, preventing super-resolved imaging...

Multiphoton microscopy has emerged as a ubiquitous tool for studying microscopic structure and function across a broad range of disciplines. As such, the intent of this paper is to present a comprehensive resource for the construction and performance evaluation of a multiphoton microscope that will be understandable to the broad range of scientific...

Exploiting the characteristics of spatially chirped ultrafast pulses has been an increasingly active area of research. In this paper, we review the developments in the past year of the microscopy, materials processing, and micromachining fields, where the spatiotemporal structure of these beams is important. We also summarize progress in theoretica...

We present a simplified approach for imaging a linear diode bar laser for application as an optical stretcher within a microfluidic geometry. We have recently shown that these linear sources can be used to measure cell mechanical properties; however, the source geometry creates imaging challenges. To minimize intensity losses and simplify implement...

Simultaneous spatial and temporal focusing (SSTF) of femtosecond pulses was originally conceived as a novel method for increasing the field-of-view in multiphoton imaging applications. Multiphoton imaging with SSTF deviated from traditional nonlinear systems in that it enabled the use of low numerical aperture beams to be used to increase the field...

A multipass chirped pulse amplification system is outfitted with a single-grating, simultaneous spatial and temporal focusing (SSTF) compressor platform. For the first time, this novel design has the ability to easily vary the beam aspect ratio of an SSTF beam, and thus the degree of pulse-front tilt at focus, while maintaining a net zero-dispersio...

We present a method using spectral interferometry (SI) to characterize a pulse in the presence of an incoherent background such as amplified spontaneous emission (ASE). The output of a regenerative amplifier is interfered with a copy of the pulse that has been converted using third-order cross-polarized wave generation (XPW). The ASE shows as a ped...

Through the development of simultaneous spatial and temporal focusing, platforms that can ablate tissue with excellent axial precision, and perform high-speed multiphoton imaging are converging. Recent developments in these platforms are presented.

Simultaneous spatially and temporally focussing (SSTF) of ultrashort pulses allows for an unprecedented control of the intensity distribution of light. It has therefore a great potential for widespread applications ranging from nonlinear microscopy, ophthalmology to micro-machining. SSTF also allows to overcome many bottlenecks of ultrashort pulse...

A watt level, 10-kilohertz repetition rate chirped pulse amplification system that has an integrated simultaneous spatial and temporal focusing (SSTF) processing system is demonstrated for the first time. SSTF significantly reduces nonlinear effects normally detrimental to beam control enabling the use of a low numerical aperture focus to quickly t...

I will present work on hybrid fiber/bulk systems employing non-linear amplifiers to reach near and mid-IR wavelengths to obtain high peak and average powers, with <100 femtosecond pulse durations. These systems have a wide range of uses from biotech imaging techniques, hard X-ray generation, and industrial/medical micromachining. I will illustrate...

Simultaneous spatiotemporal focusing (SSTF) is applied to lens tissue and compared directly with standard femtosecond micromachining of the tissue at the same numerical aperture. Third harmonic generation imaging is used for spatio-temporal characterization of the processing conditions obtained with both a standard and SSTF focus.

Spatial chirp can be manipulated to control the focusing conditions for materials processing. Our double-ABCD nonparaxial analysis helps to understand and exploit the mechanisms for intensity localization, pulse front tilt, and grating formation, and includes initial spectral phase and detuning of the wavelength crossing plane. We also present a no...

Construction of a multiphoton microscope from the excitation source, scan optics, excitation optics, collection optics, and detection electronics is described. A pragmatic, do-it-yourself approach is applied, resulting in the construction of a robust inexpensive platform. 150-word Biography: Jeff A. Squier received the B.Sc. degree in Engineering P...

Simultaneous spatial temporal focusing (SSTF) is used to deliver microjoule femtosecond pulses with low numerical aperture geometries (<0.05 NA) with characteristics that are significantly improved compared to standard focusing paradigms. Nonlinear effects that would normally result in focal plane shifts and focal spot distortion are mitigated when...

This protocol describes the application of laser pulses to image and ablate neuronal tissue for the purpose of automated histology. The histology is accomplished in situ using serial two-photon imaging of labeled tissue and removal of the imaged tissue with amplified, femtosecond pulses. Together with the use of endogenous fluorescent indicators an...

Multiphoton microscopy has enabled unprecedented dynamic exploration in living organisms. A significant challenge in biological research is the dynamic imaging of features deep within living organisms, which permits the real-time analysis of cellular structure and function. To make progress in our understanding of biological machinery, optical micr...

This chapter covers the benefits and applications of ultrafast laser scanning microscopes from a biomedical perspective. The basic architecture of a laser microscope is discussed, including how to design a laser scanning system with lateral and axial control. Also investigated is the design of custom collection optics for optimizing the detection o...

A direct-diode pumped Ti:sapphire femtosecond oscillator is used to perform multiphoton imaging for the first time.

We describe a Ti:sapphire laser pumped directly with 445nm laser diodes. With 70 mW average power at 800 nm and bandwidth for <13 fs pulses, Kerr-lens-modelocked pulses are available with dramatically decreased pump cost.

Direct diode-pumped Ti:sapphire is used to perform multiphoton imaging for the first time, and recent advances in a video-rate, multifocal, photon counting imaging systems are described.

We demonstrate a method for encoding spatial information across a line cursor using chirped amplitude modulation for application to one-dimensional multiphoton microscopy using a single-element detector. Resolution, along with imaging speed and quality, will be discussed.

We analyze the structure of space-time focusing of spatially-chirped pulses using a technique where each frequency component of the beam follows its own Gaussian beamlet that in turn travels as a ray through the system. The approach leads to analytic expressions for the axially-varying pulse duration, pulse-front tilt, and the longitudinal intensit...