Μm CO2 Laser Research Articles

Ultra-short pulse generation from mid-IR to THz range using plasma wakes and relativistic ionization fronts

This paper discusses numerical and experimental results on frequency downshifting and upshifting of a 10 μm infrared (IR) laser to cover the entire wavelength (frequency) range from λ = 1 to 150 μm (ν = 300–2 THz) using two different plasma techniques. The first plasma technique utilizes frequency downshifting of the drive laser pulse in a nonlinear plasma wake. Based on this technique, we have proposed and demonstrated that in a tailored plasma structure, multi-millijoule energy, single-cycle, long-wavelength IR (3–20 μm) pulses can be generated by using an 810 nm Ti:sapphire drive laser. Here, we extend this idea to the THz frequency regime. We show that sub-joule, terawatts, single-cycle terahertz (2–12 THz or 150–25 μm) pulses can be generated by replacing the drive laser with a picosecond 10 μm CO2 laser and a different shaped plasma structure. The second plasma technique employs frequency upshifting by colliding a CO2 laser with a rather sharp relativistic ionization front created by ionization of a gas in less than half cycle (17 fs) of the CO2 laser. Even though the electrons in the ionization front carry no energy, the frequency of the CO2 laser can be upshifted due to the relativistic Doppler effect as the CO2 laser pulse enters the front. The wavelength can be tuned from 1 to 10 μm by simply changing the electron density of the front. While the upshifted light with 5<λ(μm)<10 propagates in the forward direction, that with 1<λ(μm)<5 is back-reflected. These two plasma techniques seem extremely promising for covering the entire molecular fingerprint region.

Detection of 9.5 μm CO2 laser pulses in indium doped PbTe p-n junction

A unique feature of the PbTe semiconductor is the growth of its forbidden energy gap with increasing temperature. This allows saving diode-typical characteristics at temperatures up to 180 K. PbTe p-n diodes were fabricated by means of indium donor diffusion into PbTe single crystals grown using the Czochralski technique. The dark saturation current density was ~10−5 A/cm2 at T = 100 K, whereas at T = 180 K it reached ~10−1 A/cm2. The photovoltage signals induced by a pulsed CO2 laser light across PbTe p-n junction were investigated over the 100–180 K temperature range. The two-photon absorption-caused photovoltaic effect is observed for the first time in In doped PbTe p-n junction for 9.5 μm wavelength at T = 100 K.

Use of 9.3μm CO2 Laser for Removal of Zirconia Restorations

Objective: The primary aim of this study was to test if a 9.3µm Carbon Dioxide (CO2 ) laser could be used to effectively separate a cemented zirconia restoration from dentin. The secondary aim was to compare shear bond strength (SBS) between RelyXTM Unicem 2 Automix Cement (3M ESPE) (RelyXTM Unicem 2) and RelyXTM Luting Plus Automix Cement (3M ESPE) (RelyX™ Luting Plus). Methods: 40 teeth were prepared to expose dentin and then randomized into four groups of 10 samples. Zirconia slices (non-glazed Yttrium stabilized zirconia samples (2.5 x 3 x 1.5 mm)) were sandblasted with 50 micron aluminum oxide at 30 psi and then cemented onto the dentin samples with RelyX™ Unicem 2 or RelyX™ Luting Plus, dependent on the group. The cements were applied to both the zirconia and dentin with a force of 20 g/mm2 for 30 seconds following manufacturer’s recommendations. After 48 hours, the 9.3µm CO2 laser was used on half the samples for 5 seconds. All 40 zirconia samples were removed with the Instron 5566A in a traditional SBS test. The groups were: 1A - RelyX™ Unicem 2 and Laser, 1B - RelyX™ Unicem 2 and Shear Bond, 2A - RelyX™ Luting Plus and Laser, and 2B - RelyX™ Luting Plus and Shear Bond. The Mann–Whitney U test was used for comparison. Results: Mean SBS of four groups ranged from 0.5 to 4.4 MPa. There was a significant difference in the SBS between 9.3µm CO2 laser and Shear Force methods for RelyX™ Luting Plus. However, the difference between the two methods was not significant for RelyX Unicem 2. RelyX™ Unicem 2 provided significantly higher SBS than RelyX™ Luting Plus for both the CO2 laser and shear force methods (Table 2). Conclusion: The 9.3µm CO2 laser effectively separated the zirconia restoration cemented with RelyX™ Luting Plus from dentin. RelyX™ Unicem 2 provided significantly stronger SBS than RelyX™ Luting Plus.

Comparison of Live Bacteria Aerosolization during Removal of Dental Enamel Using a 9.3μm CO2 Laser, a 2.78μm Erbium Laser and a High-Speed Dental Drill

Purpose: To measure the amount of viable pathogens in the aerosol/splatter generated during dental procedures using lasers and high-speed drill. Methods: Three systems were used in this in vitro study: 9.3μm CO2 laser, 2.78μm erbium laser and a high-speed drill. 45 uncleaned human molars were randomly selected to be used for the test groups for the three systems. Bacteria ejected while cutting the buccal or lingual surfaces were collected on tryptic soy agar (TSA) plates in identical conditions for each measurement. On the opposite surface of each tooth, a non-cutting mist spray was applied. Results: The CO2 laser resulted in colony-forming units (CFU) with a mean of 1570 ± 3850 CFU/m3/s, which is statistically different (p < 0.001) relative to both the erbium laser and the drill with a mean of 185,000 ± 182,000 CFU/m3/s and 440,000 ± 496,000 CFU/m3/s, respectively. CFU measured from the non-cutting mist spray on the teeth was higher for the drill than for the lasers. Conclusion: The 9.3μm CO2 laser resulted in the lowest CFU in the aerosol/splatter during enamel removal as compared to that of the 2.78μm erbium laser and the traditional high-speed drill. Furthermore, the CO2 laser was the only system that did not increase aerosolization of bacteria while cutting compared to the non-cutting mist spray.

Demineralization Inhibition by High-Speed Scanning of 9.3 µm CO2 Single Laser Pulses Over Enamel.

In vitro studies were conducted to evaluate the use of an automated system for high-speed scanning of single 9.3 µm CO2 laser pulses in the inhibition of caries-like lesion formation in the enamel of extracted human molars. The effect of the laser in generating an acid-resistant layer and the effect of the layer on inhibiting surface mineral loss during pH cycling was explored. Laser irradiation was performed with fluences of 0.6, 0.8, and 1.0 J/cm2 for single pulses of 1 mm diameter (1/e2 ), with pulse durations of 17, 22, and 27 microseconds, respectively. The laser was scanned at a 750 Hz pulse repetition rate in an automated pattern covering an area of 7 mm2 in 0.3 sec. Six treatment groups were investigated: three groups for each fluence for laser-only and three for laser irradiation with additional fluoride from a toothpaste slurry (sodium fluoride at 1100 ppm). Each group used non-irradiated areas, which included untreated controls for the laser-only groups and a fluoride-only treatment for the groups with additional fluoride. pH cycling was performed on both groups, followed by microhardness testing to determine the relative mineral loss (∆Z) from a caries-like formation and surface mineral loss (∆S). Laser irradiation with the 9.3 µm CO2 laser generated an acid-resistant layer of about 15 µm in depth. For the laser-irradiated samples with additional fluoride application, the relative mineral loss (∆Z) was 113 ± 63 vol%-µm, while for those with only fluoride application ∆Z was 572 ± 172 vol%-µm. At the highest fluence (1.0 J/cm2 ) used, an 80.2% inhibition of caries-like lesion was measured by ∆Z. Using only laser irradiation at the highest fluence resulted in an inhibition of caries-like lesion of 79.5% for the irradiated samples (∆Z = 374 ± 149 vol%-µm) relative to the control (∆Z = 1826 ± 325 vol%-µm). Surface microhardness tests resulted in an inhibition of surface softening, as measured by the Knoop Hardness Value (KHN) (108 ± 33 KHN for laser irradiated with additional fluoride, for non-irradiated controls with fluoride only 52 ± 16 KHN). Inhibition of surface loss was observed for all laser fluences, but the maximum surface loss for the untreated control group was only 2.2 ± 0.49 µm. The results demonstrate a significant benefit of the 9.3 µm CO2 laser at fluences of 0.6, 0.8, and 1.0 J/cm2 in caries-like lesion inhibition as measured by the relative mineral loss in depth and surface mineral loss, without significant damage to the enamel. Additionally, inhibition of surface softening and surface loss during pH cycling was observed. The surface loss was small compared with the overall lesion depth and thickness of the generated acid-resistant layer. Lasers Surg. Med. © 2020 Wiley Periodicals LLC.

Microshear Bond Strength of Composite Resin to Enamel Treated With Titanium Tetrafluoride and the Carbon Dioxide Laser (10.6 µm): An In Vitro Study.

Introduction: The present study aims to assess the microshear bond strength (µSBS) of composite to enamel treated with titanium tetrafluoride (TiF4 ) and CO2 laser irradiation. Methods: Fifteen human molars were sectioned and their enamel surfaces were abraded. The sections were randomly assigned to 5 groups (n=15): (CO); control group, (AP); treated with 1.23% acidulated phosphate fluoride (APF) for 4 minutes, (Ti); 4% TiF4 for 1 minute, (L+AP); CO2 laser irradiation (10.6 µm wavelength, 1 W peak power, 10 ms pulse duration, 500 ms repetition time, 0.2 mm beam spot size at the tissue level, 2 cm distance of handpiece tip to tissue surface (DSE, South Cores) followed by 1.23% APF, and (L+ Ti); 10.6μm CO2 laser irradiation followed by 4% TiF4 for one minute. Using Tygon tubes, Z250 (3M/ESPE) composite was bonded to the surface of the samples. The µSBS of composite to enamel was measured using a microtensile testing machine after 500 thermal cycles. The data were analyzed by one-way ANOVA and the Tukey HSD test (P <0.05). Results: The mean µSBS was 20.66, 20.21, 13.44, 23.01, and 10.16 MPa in CO, AP, Ti, L+AP, and L+Ti groups respectively. Significant differences were observed between CO and Ti (P =0.026) and also CO and L+ Ti (P <0.0001). Conclusion: The application of TiF4 per se and after CO2 laser irradiation on enamel decreased the µSBS of composite to enamel; on the other hand, APF alone and after laser irradiation did not have any adverse effect on the µSBS of composite to enamel.

Electrical modulation of the LWIR absorption and refractive index in InAsSb-based strained layer superlattice heterostructures

InAsSb-based strained layer superlattices (SLS) have strong fundamental absorption, which can be easily modified in a controlled manner by injecting excess carriers. This makes them attractive for intensity modulation of infrared lasers as well as beam steering and spatial beam shaping with a nanosecond-scale time response. This paper reports the modulation of the fundamental absorption and the refractive index by carrier injection in a 3.45-nm-period InAsSb0.65/InAsSb0.35 SLS with a low temperature energy gap of 85 meV grown by molecular beam epitaxy on a GaSb substrate with a GaInSb metamorphic buffer. The SLS absorber was sandwiched by n- and p-type wider energy gap layers for electrical injection and confinement of excess carriers. The population of conduction band states was obtained by measuring the intensity modulation of a 10.6 μm CO2 laser for temperatures ranging from T = 77 to 200 K. An increase of the electron quasi-Fermi level with electrical injection up to 20 meV was observed. The experimental data imply a decrease in the Auger coefficient with temperature, from 3 × 1024 cm6/s at 77 K to 1 × 1024 cm6/s at T = 200 K attributed to recombination involving two electrons and a heavy hole. The refractive index changes obtained by electrical injection of excess carriers can reach 0.05 at T = 77 K and 0.035 at T = 200 K, which are at least three orders of magnitude greater than those obtained with electro-optical materials.

High Gain Coefficient Parametric Amplification of Optical Phonon Mode in Magnetized AIIIBV Semiconductor Plasmas

Using the hydrodynamic (fluid) model of plasmas, we have studied the threshold and gain characteristics of parametric amplification of optical phonon mode in magnetized AIIIBV semiconductor plasmas. The origin of nonlinear interaction is assumed to lie in second-order nonlinearity arising due to nonlinear coupling of pump wave, optical phonon and signal modes in the medium. Theoretical formulation has been carried out with the help of coupled mode theory under rotating-wave approximation. Numerical estimates have been made for a representative magnetized doped AIIIBV semiconductor crystal (viz. n-InSb) irradiated by a pulsed 10.6 μm CO2 laser. The analysis enables us to choose one of the three achievable resonance conditions: (electron–cyclotron frequency ~ pump frequency, coupled cyclotron– plasmon frequency ~ Stokes frequency, coupled cyclotron–plasmon frequency ~ optical phonon frequency), at which threshold pump amplitude reduces, whereas parametric gain coefficient enhances nearly hundred times. The lowering of threshold and enhancement of parametric gain coefficient, in AIIIBV semiconductors under proper selection of doping concentration and externally applied magnetic field, confirm the chosen nonlinear medium as a potential candidate material for fabrication of optical parametric amplifier with enhanced gain coefficient.

Understanding the Thermal Denaturation of Myoglobin with IMS-MS: Evidence for Multiple Stable Structures and Trapped Pre-equilibrium States.

Thermal denaturation of holomyoglobin (hMb) in solution (10 mM ammonium acetate at pH = 4.5, 6.8, and 9.0) was monitored by ion mobility spectrometry (IMS) and mass spectrometry (MS) techniques to characterize the stability and investigate structural changes involved in unfolding. We utilize two experimental approaches to induce thermal denaturation: a variable-temperature electrospray ionization (vT-ESI) source that heats the bulk solution in the ESI emitter, and a variable-power 10.6 μm CO2 laser that rapidly heats nanodroplets produced by ESI. These two approaches sample different time scales of the denaturation process; long time scales (seconds to minutes) where the system is at equilibrium using the vT-ESI approach and shorter time scales (μs) by rapid droplet heating in which the system is in a pre-equilibrium state. Increasing the solution temperature (from 28 to 95 °C in the vT-ESI experiments) shifts the charge state distribution from low charge states ([M + 7H]7+ to [M + 9H]9+) to more highly charged species. This is accompanied by loss of the heme group to yield the apomyoglobin (aMb) species, indicating that the protein has unfolded. Monitoring the formation of aMb and the shift in average charge states of aMb and hMb with solution temperature allows for relative quantitation of their individual stabilities, highlighting the stabilizing effects of heme binding. We compare the degree of unfolding induced by heating the bulk solution (using vT-ESI) to the laser droplet heating approach and find that the rapid nature of the laser heating approach allows for transient pre-equilibrium states to be sampled.

Replacing the metal electrodes in triboelectric nanogenerators: High-performance laser-induced graphene electrodes

Abstract While significant work is being carried out to develop materials for enabling high surface charge density triboelectric nanogenerators (TENG), little attention has been paid to the role of electrodes responsible for charge collection. This work reports on the facile synthesis and use of high crystallinity, sp2-hybridised laser-induced graphene (LIG) as a high-efficiency electrode for triboelectric nanogenerators (TENGs). Using a conventional 10.6 μm CO2 laser, the controlled, direct photothermal conversion of dielectric, tribo-negative polyimide (PI) and tribo-positive cellulosic paper into corresponding PI-LIG and paper-LIG, respectively, facilitates a significantly higher electrical output as compared to the commonly utilised adhesive aluminium electrodes. The LIG based paper-PI TENGs showed significantly higher electrical output characteristics with a peak-to-peak voltage of up to ~625 V, a current density of ~20 mA m−2 and a transferred charge density of ~138 μC m−2 with a maximum power output of ~2.25 W m−2, respectively, while the corresponding values for the conventional Al-tape electrode-based paper-PI TENGs were 400 Vp-p, ~10 mA m−2, ~85 μC m−2 and 0.9 W m−2, respectively. The mechanically robust LIG electrodes show excellent stability with less than 5.0% variation in output over 12,000 contact cycles. Using Kelvin probe force microscopy (KPFM) measurements, we have measured differences in not only the average surface potentials of the triboelectric surfaces (−0.26 V for pristine PI vs. +0.34 V for paper, which drive the TENG electrical output) but also for the LIG's synthesised from them (−0.08 V for PI-LIG vs. +0.26 V for paper-LIG), suggestive of the role of initial surface chemistry in the formation of LIGs. The enhanced (~150%) power density for LIG based TENGs is ascribed to the lowering of the charge transfer barrier height via the alignment of Fermi levels resulting in higher surface charge on the dielectric surface and the significantly (~6 orders) lower interfacial contact impedance of LIG as compared to adhesive aluminium electrodes. Thus, via the removal of the additional interface between the triboelectric surface and electrode, high-performance metal-free TENGs with excellent prospects for enabling energy harvesting applications can be realised.

Self-focusing and pulse sharpening of sub-picosecond laser pulse in n-InSb

The self-focusing and pulse sharpening of an intense short pulse laser in n-type indium antimonide, a semiconductor with non-parabolic energy band, is studied. The nonlinearity arises through the dependence of electron effective mass on quiver velocity and gives effective permittivity a saturating function of intensity. A laser beam with Gaussian transverse intensity profile undergoes periodic self-focusing. The faster self-focusing of the peak of the pulse causes significant sharpening of the pulse in course of propagation. For 10.6μm CO2 laser of picosecond pulse length and intensity ∼1 – 2 GW/cm2, significant self-focusing and pulse length shortening occurs over a length of 0.6 mm.

Computational Tracking of Dental Splatter: Comparison of HighSpeed Drill and 9.3µm CO2 Laser

Computational Tracking of Dental Splatter: Comparison of HighSpeed Drill and 9.3µm CO2 Laser

Effect of 9.3μm CO2 Laser and Fluoride on Shear Bond Strength, Microleakage, Acid Resistance and Microhardness of Sealants

Effect of 9.3μm CO2 Laser and Fluoride on Shear Bond Strength, Microleakage, Acid Resistance and Microhardness of Sealants

Wavelength-Switchable Fiber Laser Based on Long-Period Fiber Grating Written on Polarization-Maintaining Photonic Crystal Fiber.

Here we propose a wavelength-switchable erbium-doped fiber ring laser using a temperatureinsensitive spectral polarization-dependent loss (PDL) element and two fiber Bragg gratings (FBGs). The fiber PDL element was fabricated by inscribing a long-period grating (LPG) on polarizationmaintaining photonic crystal fiber (PMPCF) with a 10.6 μm CO₂ laser. The LPG fabricated on PMPCF, referred to as PMPCF-LPG, has the characteristics of a fiber polarizer at two specific wavelengths due to the birefringence of PMPCF and the co-directional mode coupling of the LPG. The two wavelengths at which the fabricated PMPCF-LPG acts as a polarizer are two resonance wavelengths (~1528.58 and ~1555.90 nm) of the PMPCF-LPG, obtained for orthogonal input polarization states. By considering these two resonance wavelengths of the PMPCF-LPG, the Bragg wavelengths of two FBGs, which determine lasing wavelengths in our wavelength-switchable laser, were selected as ~1527.71 and ~1554.74 nm. As the temperature sensitivity of the PMPCF birefringence is 30 times lower than that of the birefringence of conventional polarization-maintaining fiber (PMF), the fabricated PMPCF-LPG could facilitate more stable switching operation between the two lasing wavelengths in comparison with a previous fiber laser employing an LPG inscribed on conventional PMF as a wavelength-switching filter. The lasing wavelengths of our laser could be switched by controlling input polarization of the PMPCF-LPG with a polarization controller, and temperature-insensitive wavelength switching operation was experimentally demonstrated over a temperature range of 25-100 °C.

Tooth Preparation with a 9.3 µm CO2 Laser Reduces Demineralization around Dental Restorations

Tooth Preparation with a 9.3 µm CO2 Laser Reduces Demineralization around Dental Restorations

Transient amplification characteristics of frequency modulated wave in semiconductor plasmas

We perform an analytical investigation of modulational interaction of an electromagnetic pump wave in a transversely magnetized weakly polar semiconductor plasma medium. Based on the hydrodynamic model, a critical examination of frequency modulational amplification is made in a moderately doped III–V semiconductor crystal (n-GaAs) duly shined by pulsed 10.6 µm CO2 laser. The effect of electron-LO phonon interaction and coupled magnetoplasma excitations on the nonlinear interaction of a laser beam adds new dimension to the analysis. Steady state and transient gain coefficients, threshold pump intensity and optimum-pulse duration for the onset of modulational instability are estimated. The paper concentrates on the study of gain characteristics mainly in transient region. Effect of doping and applied magnetic field on the threshold pump intensity and growth rate has been significantly analysed. Graphical analysis interprets strong dependence of transient amplification characteristics on these parameters. So a judicious choice of physical parameters may develop growth at much lower pump intensity improving the cost effectiveness of the system. These results may help to be important for understanding and improving the performance of modulator.

10.6 μm CO2 레이저용 F-theta 렌즈의 설계 개발

10.6 μm CO2 레이저용 F-theta 렌즈의 설계 개발

Fabrication and bending strength analysis of low-loss Ge15As25Se40Te20chalcogenide glass fiber: a potential mid-infrared laser transmission medium

Low-loss optical fibers of Ge15As25Se40Te20 glass purified by combined chemical and physical methods were successfully drawn. A novel fabrication method of fiber preform was adopted by wrapping a 1 mm thick polyethersulfone (PES) plastic tube around the glass rod. The optical, thermal, and bending strength properties of the glass and fiber were comprehensively investigated. The minimum transmission loss of the fiber was measured as 0.6 dB/m at 6.05 µm, and the average bending strength was approximately 180.67 MPa with a Weibull slope of 49.18 for a 400 µm fiber diameter. Optical power transmission characteristics of a 10.6 µm CO2 laser beam were also studied. The maximum transmitting power through a 1 m long and 400 µm diameter fiber was 1.37 W, which corresponded to a power density of 1.09 kW/cm2 at the fiber output end. Therefore, this fiber is suitable for infrared applications, e.g. mid-infrared laser transmission.

Laser-Induced Graphene for Flexible and Embeddable Gas Sensors.

Laser-induced graphene (LIG) has received much attention since it enables simple and rapid synthesis of porous graphene. This work presents a robust direct-write LIG-based gas sensor, which senses gases based on thermal conductivity, similar to a katharometer sensor. The gas sensors are fabricated by lasing polyimide substrates with a 10.6 μm CO2 laser to synthesize LIG. This enables the formation of flexible gas sensors which could be incorporated on a variety of surfaces. High surface area and thermal conductivity of the LIG results in rapid response times for all studied gases. The gas sensors are also embedded in cement to form a refractory composite material. These sensors are used to determine composition of various gas mixtures, such as N2 and CO2, which are the most abundant gaseous species in flue gas. Thus, LIG based embeddable sensors could be incorporated in composites to enable electronically functional construction materials.

Preventive effects of carbon dioxide laser and casein phosphopeptide amorphous calcium phosphate fluoride varnish on enamel demineralization: A comparative, in vitro study.

The aim of the present study was to compare the effects of carbon dioxide (CO2 ) laser and casein phosphopeptide amorphous calcium phosphate (CPP-ACP)fluoride varnish on enamel demineralization. Human teeth were randomly assigned to three groups. The enamel was treated with fluoride varnish, 10.6μm CO2 laser, or no treatment (control), followed by 9days of pH cycling. Baseline and final FluoreCam images were used to quantify the area, intensity, and impact of demineralization; cross-sectional microhardness was used to measure the mechanical properties of the enamel. There were statistically-significant changes in the area, intensity and impact of demineralization in the control and laser groups (P<0.05), but not in the fluoride group. The control group showed a significantly greater area and impact of enamel demineralization compared to the fluoride group. The area of demineralization in the laser group was significantly greater than that of the fluoride group. Enamel demineralization of the laser and control groups was comparable. The fluoride group showed statistically-significant harder enamel than the control at 20, 40, and 60μm depths; the laser group enamel was significantly harder than the control at 20 and 40μm depths. The fluoride group showed statistically-significant harder enamel than the laser group at 20μm depth. CPP-ACP fluoride varnish is more effective than CO2 in preventing enamel demineralization.