Dawson T. Nodurft

Enabling time resolved microscopy with random Raman lasing

Optical imaging of fast events and processes is essential for understanding dynamics of complex systems. A bright flash of illuminating light is required to acquire sufficient number of photons for superior image quality. Laser pulses can provide extreme brightness and are typically employed to achieve high temporal resolution; however, the high degree of coherence associated with the lasing process degrades the image quality with speckle formation. Random lasers are low-coherence sources of stimulated emission and do not suffer from speckle, but are rather broadband and have a relatively low output power limiting the scope of their potential applications. In this report, we demonstrate the use of random Raman lasing as a novel imaging light source with unprecedented brightness for a speckle-free and narrowband light source. We showcase the advantages of a random Raman laser to image the nanosecond scale dynamics of cavitation formation in water and quantitatively compare these images to those taken with incoherent fluorescent emission and coherent laser light as illumination source.

Zinc selenide: an extraordinarily nonlinear material

Zinc Selenide (ZnSe) has long been recognized as a nonlinear optical material and is used in many optoelectronic devices such as light emitting diodes. ZnSe is known for its remarkably wide transmission range for infrared radiation leading to its use in infrared laser applications. In this report, we discuss higher order harmonic generation when exposing ZnSe to tunable femtosecond mid-IR laser pulses with wavelengths ranging from 2.7 μm to 8.0 μm and pulse energies between 3 and 17 μJ. Higher order harmonic generation was in some instances strong enough to be directly seen by the unaided eye. We also compare these results with measurements taken for other optical materials.

Rainbow from nowhere (Conference Presentation)

Filamentation in air is a profound effect caused by high energy photons. While it has been studied in a wide-range of laser systems, there still exist wavelength regimes where filamentation hasn’t been created, due to lack of sources. Using a tunable near-infrared femtosecond laser, we generated filamentation in air by wavelengths from 1.2 to 2.5 µm. The observed filaments produced harmonic and continuum generation well into the visible spectrum; a rainbow of colors.

Visible supercontinuum generation from a tunable mid-infrared laser

Calcium fluoride, BK7 and fused silica are common optical materials used in lenses and windows. In this report, we discuss supercontinuum generation using tunable femtosecond mid-IR laser pulses with wavelengths ranging from 2.7 μm to 7.0 μm and pulse energies between 3 and 18 microjoules. We observed harmonic generation in fused silica and BK7, but not supercontinuum generation. Other borosilicate targets generated supercontinuum in both visible and near infrared regions of the spectrum. The visible supercontinuum was, in some instances, strong enough to be observed directly by the human eye. These results contribute to ongoing work being done to refine eye safety standards for femtosecond lasers.

Chemical, biological, and trace gas detection and measurement with a newly developed integrating Cavity Enhanced Raman (iCERS) technique

Raman spectroscopy is routinely used in the laboratory for detection, chemical identification, and quantitative measurements of complex molecular compounds. One key advantage of the method is that a single laser wavelength can be used to identify and measure several different molecular compounds simultaneously. While Raman spectroscopy is a powerful technique, it is a very inefficient process where only one in 1011 scattered photons contain the desired vibrational information. Several techniques have been developed to enhance Raman scattering, which are typically applied to liquids and solids such as surface enhanced Raman spectroscopy and coherent anti-Stokes Raman spectroscopy. For gas phase measurements, photonic crystals, cavity enhanced Raman spectroscopy and functional waveguides have been developed to provide Raman enhancement. However, Raman spectroscopy has seen limited use in commercial and military applications due to instrument complexity, sample preparation, acquisition time, and spatially localized point measurements. A recently developed technique to enhance spontaneous Raman scattering utilizing a highly reflective integrating cavity is presented. Elastically scattered light circulates within the cavity volume continuously interacting with the sample, whether a bulk sample or gas, resulting in significant Raman enhancement. In addition, the Raman scattered light is collected from all directions before being coupled out of the cavity. Enhancements of 107 have been realized with the use of inexpensive low power diode lasers and a modest CCD based spectrometer. Application of the iCERS technique operating near 400 nm providing near real-time detection and measurement of trace gases, chemicals, and biological compounds is discussed.

Towards optical brain imaging: getting light through a bone

Abstract Optical imaging and detection in biological samples is severely limited by scattering effects. In particular, optical techniques for measuring conditions beneath the skull and within the bone marrow hold significant promise when it comes to speed, sensitivity and specificity. However, the strong optical scattering due to bone hinders the realization of these methods. In this article, we propose a technique to enhance the transmittance of light through bone. This is achieved by injecting light below the top surface of the bone and utilizing multiple scattering to increase transmittance. This technique suggests that enhancements of 2–6 times may be realized by injection of light 1 mm below the surface of the bone. By enhancing the transmittance of light through bone, we will greatly improve our ability to utilize optical methods to better understand and diagnose conditions within biological media.

Brillouin micro-elastography of laser-processed materials

3D laser processing is becoming a mainstream of micro- and nano- fabrication. However, very little is known how physical, chemical and/or structural changes induced by laser irradiation affect local mechanical properties. In this report, we, for the first time, utilize Brillouin microspectroscopy to assess and image the variation of viscoelastic properties of materials induced by laser processing.

Damage thresholds in skin and cornea using tunable ultrafast lasers

The market for ultrafast lasers (picosecond and femtosecond laser pulses) is rapidly expanding and recent forecasts estimate a total market of over

Lighting up microscopy with random Raman lasing

1.4 billion USD by 2019. Ultrafast lasers have many applications in biomedicine, telecommunications, defense, materials processing, and general research. Despite the growing adoption of ultrafast laser technology, current safety standards (ANSI Z136.1-2014) do not include maximum permissible exposure (MPE) values for skin using laser applications with pulse durations less than one nanosecond. Moreover, the wavelength dependence of ultrafast laser exposure in the mid-infrared region of the spectrum has not been explored. Increasing prevalence of ultrafast lasers will likely lead to an increase in the number of adverse events from accidental exposures.Our objective was to use a tunable femtosecond regenerative amplifier and an optical parametric amplifier (Spectra-Physics, Irvine, CA) to investigate laser damage characteristics and exposure thresholds for tissue phantoms mimicking the cornea and skin. The laser system covers a range of wavelengths from 1200-2900 nm with pulse energies from tens of microjoules to three millijoules. Multiple parameters including wavelength, spot size, and pulse repetition were evaluated.Additional data observing ultrafast laser exposure to ocular tissue and skin are still needed to establish MPE values for the safety standards. This initial study will help guide future experiments, standards, and promote the safe use of ultrafast laser technology across a wide range of applications and disciplines.The market for ultrafast lasers (picosecond and femtosecond laser pulses) is rapidly expanding and recent forecasts estimate a total market of over

Raman spectroscopy compatible PDMS droplet microfluidic culture and analysis platform towards on-chip lipidomics

1.4 billion USD by 2019. Ultrafast lasers have many applications in biomedicine, telecommunications, defense, materials processing, and general research. Despite the growing adoption of ultrafast laser technology, current safety standards (ANSI Z136.1-2014) do not include maximum permissible exposure (MPE) values for skin using laser applications with pulse durations less than one nanosecond. Moreover, the wavelength dependence of ultrafast laser exposure in the mid-infrared region of the spectrum has not been explored. Increasing prevalence of ultrafast lasers will likely lead to an increase in the number of adverse events from accidental exposures.Our objective was to use a tunable femtosecond regenerative amplifier and an optical parametric amplifier (Spectra-Physics, Irvine, CA) to investigate laser damage characteristics and exposure thresholds for tissu...