Tunable Pulsed Laser Research Articles

Growth and spectroscopic properties for Ho3+:SrGdGa3O7 crystal

The Ho3+:SrGdGa3O7 single crystal was grown by the Czochralski method. The polarized absorption spectra, emission spectra and fluorescence decay curve of the crystal were measured at room temperature. The absorption cross-sections, corresponding to 5I8→5G6+5F1 absorption bands, are 4.4×10−20cm2 for π polarization and 3.5×10−20cm2 for σ polarization. Based on the Judd–Ofelt theory and the polarized absorption spectra, the spontaneous transition probabilities, the fluorescent branching ratios and the radiative lifetimes were calculated. The crystal exhibited a broad emission band from 1900nm to 2100nm and the stimulated emission cross-section at 1990nm is 1.01×10−21cm2. The fluorescence lifetime of 5I7 multiplet of Ho3+ ions is up to 9.17ms. The results show that the Ho3+:SrGdGa3O7 crystal is a promising gain medium for tunable and ultrashort pulse lasers operating around 2.0μm.

Broadly wavelength tunable acousto-optically Q-switched Tm:Lu2SiO5 laser.

A broadly wavelength tunable acousto-optically Q-switched Tm:Lu2SiO5 (Tm:LSO) laser is presented for the first time, to our best knowledge. The emission wavelength was tuned in a broad spectral region over 111 nm ranging from 1959 to 2070 nm. A shortest pulse duration of 345 ns with beam quality of M(2)≤1.65 was obtained at pulse repetition frequency (PRF) of 1 kHz, corresponding to a maximum single pulse energy of 0.26 mJ and peak power of 0.75 kW. The experimental results indicated that Tm:LSO crystal has outstanding potential for obtaining broadly wavelength tunable and low-PRF laser pulses at 2 μm.

Time-, angle- and kinetic-energy-resolved photoelectron spectroscopy of highly excited states of NO

We investigate non-adiabatic dynamics of NO molecules that are photo-excited in the vacuum ultraviolet photon energy range using time-resolved velocity map imaging. Highly excited valence and Rydberg states are populated with a tunable (147–151 nm) femtosecond laser pulse and then ionized by a time-delayed near-IR laser pulse. Three main contributions are observed in the photoelectron kinetic spectra with corresponding electron yields that show pronounced oscillations. Two oscillations are assigned to ro-vibronic coupling in the valence-Rydberg mixture of the B and 4dδ N2Δ(v = 0) states and the B2Π(v = 25) and 4pπ K2Π(v = 1) states, respectively. We assign a third oscillation to originate from a coupling between two Rydberg states.

Development of a 1J short pulse tunable TEA CO2 laser with high energy stability

Abstract The design, development and operational characteristics of a 1 J, repetitively pulsed, line tunable TEA CO2 laser producing nearly tail free short pulses (~170 ns) suitable for laser isotope separation is discussed. Tail free short laser pulses were generated by employing a nitrogen lean gaseous active medium. Use of an indigenously developed stable pulsed power supply, uniform and intense UV spark pre-ionization and optimum gas purging with catalytic regeneration to control the deleterious oxygen accumulation helps generate laser pulses with high energy stability. Integration of a sensitive arc detection system allows long term arc-free operation of the laser and protects it from catastrophic failure. Laser pulses in more than 90 lines in 10.6 µm and 9.6 µm bands of CO2 laser spectrum with energy about 1 J in as many as 50 lines could be generated with a typical efficiency of about 4%. A typical pulse to pulse energy stability of ±1.4% was obtained during one hour of continuous operation of the TEA CO2 laser at 75 Hz.

New even-parity high-lying levels of Sm I and measurement of isotope shifts by two-color resonance ionization mass spectrometry

In this work, we investigate the even-parity high-lying levels of Sm I in the energy region 33136–33960cm−1 by performing two-color three-photon resonance ionization spectroscopy in an atomic beam coupled to a time-of-flight mass spectrometer using two tunable pulsed dye lasers. We observe twenty-one new and confirm eight previously reported even-parity energy levels of Sm I in this spectral region. Absolute energies of these levels are determined with an accuracy of ±0.3cm−1. Using electric dipole selection rule, total angular momentum (J-value) of the most newly observed levels is assigned uniquely. Further, employing two-color three-step resonance ionization mass spectrometry, we measure the isotope shift between 154Sm and 144Sm of sixteen high-lying levels with a moderate accuracy of ±30mK.

Growth, thermal and spectral characteristics of Yb3+:Sr6YSc(BO3)6 crystal

Abstract A crystal of Yb 3+ :Sr 6 YSc(BO 3 ) 6 was grown successfully from Li 6 B 4 O 9 flux by the top-seeded solution growth method. The crystal's thermal, mechanical and spectral characteristics were investigated in detail. It possesses small thermal expansion coefficients, moderate thermal conductivities, and large hardness. The crystal has a strong absorption band at 967 nm with a full width at half-maximum of about 3.4 nm. The crystal has a broad emission band at 1016 nm with the full width at half-maximum of about 64 nm. The emission cross sections were calculated by reciprocity method and Fuchtbauer-Ladenburg formula. The fluorescence lifetime is 5.98 ms. The results reveal that Yb 3+ :Sr 6 YSc(BO 3 ) 6 crystal is a new promising tunable and ultrashort pulse laser crystal.

Generation of tunable narrowband laser pulses in the ultraviolet with a pulsed dye amplifier seeded by a near-infrared diode laser

We demonstrate the generation of narrowband laser pulses in the ultraviolet (UV) region with a continuous tunability over 10GHz. To realize such pulses we construct a four-pass pulsed dye amplifier with an external cavity diode laser (ECDL) at the near-infrared (NIR) region as a seed laser, and do the frequency doubling. The achieved pulse energy is about 10μJ at 369.4nm with a 230±20MHz bandwidth and 3.3±0.2ns pulse duration.

Carrier-envelope phase passively stabilized near-infrared laser pulses from a dual-frequency pumped noncollinear optical parametric amplifier

By inversing the signal and idler in a two-stage noncollinear optical parametric amplifier which is, respectively, pumped by the second harmonic and fundamental wave of femtosecond Ti:sapphire laser at repetition rate of 1 kHz, the carrier-envelope phase (CEP) passively stabilized pulses with a tunable wavelength from 1.1 to 1.6 μm are obtained with maximum energy of 95 μJ at 1.3 μm under the pump energy of 500 μJ. The CEP jitter of pulses is 108 mrad measured by an f-2f interferometer. This work demonstrates a new way to efficiently generate tunable near-infrared femtosecond laser pulses with self-stabilized CEP.

Crystal Growth and Spectroscopic Investigations of Tm3+:Li₃Ba₂Gd₃(MoO₄)₈ Crystal.

Tm3+:Li3Ba2Gd3(MoO4)8 crystal has been grown by the top seeded solution growth (TSSG) method from a Li2MoO4 flux. The room temperature polarized absorption spectra, fluorescence spectra, and fluorescence decay curves of the crystal were measured. Based on the Judd-Ofelt (J-O) theory, the main spectroscopic parameters of the crystal, including the spontaneous emission probabilities, fluorescence branching ratios, and radiative lifetimes were calculated and analyzed. The broad and strong absorption bands of the crystal show that it can be efficiently pumped by the diode laser, while the large emission cross-sections of the 3F4 → 3H6 transition indicate that the crystal is a promising candidate for tunable and short pulse lasers.

Cr3+-doped CaMgSi2O6crystal: a promising tunable laser and ultrashort laser crystal

This paper reports the growth and spectral properties of the Cr3+:CaMgSi2O6 (Cr3+:CMS) crystal. The Cr3+:CMS crystal was grown by the Czochralski method. Investigation of its spectral properties shows that the Cr3+:CMS crystal has broad, strong absorption and emission cross-sections. It has two broad absorption bands which center at 460 nm and 652 nm. The emission cross-section σe at 986.1 nm is 14.39 × 10−20 cm2 at 300 K. The emission FWHM is up to 212 nm. Therefore, the Cr3+:CMS crystal can be considered as a potential tunable and ultrashort pulse laser crystal.

Constitutive Modelling and Histology of <i>Vena saphena</i>

The inflation-extension test was performed in order to obtain the mechanical response (stress-strain curves) of the human vein - vena saphena magna (usually used for coronary artery bypass graft surgery). Tubular samples of the vein were inflated four times up to the pressure approx. 4 kPa (vein pressure) and then four times up to approx. 16 kPa (systolic pressure). The experiments were recorded by the CCD camera. The longitudinal and circumferential deformations of the tube were evaluated using the edge detection method. The experimental data were fitted by anisotropic, nonlinear, constitutive model in order to obtain model parameters, especially the parameter which can be explained as collagen fibres orientation approximation. This parameter was then compared with the findings from histology. The histology analyses based on label-free imaging were performed additionally to the mechanical testing. Collagen (most important load-bearing component of the vein wall) was visualized using second harmonic generation imaging (SHG, excitation at 860 nm by a tunable IR pulse laser, detection at 430±10 nm). This method enabled us to observe collagen through the vein wall. It was found that the collagen fibres are helically aligned within the vein at an angle 37±6° measured from circumferential axis. The results of collagen orientation angle show a good agreement of findings obtained from histology and from constitutive model.

Optical characterization of GaAs photoconductive antennas for efficient generation and detection of Terahertz radiation

We report the optical characterization of low temperature (LT)-GaAs and Semi Insulating (SI)-GaAs based dipole types Photoconductive (PC) antennas with gap of 5μm for the generation and detection of Terahertz (THz) signals. We have used tunable 140femto-seconds laser pulses at 80MHz repetition rate of different power and biasing voltage to evaluate the performance of our antennas as a THz generator and detector. Interestingly, we found that LT-GaAs and SI-GaAs have high photocurrent (density of charge carriers) response at some specific laser wavelengths such as 840nm and 880nm, respectively. We have employed these selected wavelengths for the generation and detection of THz radiation from these materials made PC antennas. The comparative study shows that the intensity of THz radiation in case of SI-GaAs is higher than the LT-GaAs made PC antennas. The THz frequency spectrum range of LT-GaAs and SI-GaAs antennas are extended up to 3.6THz and 2.5THz respectively. Finally, we have cross verified the reliability of our antennas to detect the THz radiation generated from ZnTe crystal.

Clinical efficacy of the 595 nm pulsed dye laser in the treatment of childhood superficial hemangioma – analysis of 10-year application in Chinese patients

Background: The 595 nm tunable pulsed dye laser has been used in China for more than 10 years. However, no studies about its effect and side-effect in treatment of superficial hemangioma have been documented. Objective: This study was designed to retrospectively summarize its usage in Chinese patients. Methods: Infant patients with superficial hemangioma, who had received 595 nm tunable pulsed dye laser treatment in our laser center in the last 10 years, were recruited. Detailed demographics, results of assessment about their degree of clearance and clinical examination for treatment complications were entered into SASS10.0 version database, and statistical analyses were conducted. Results: Six hundred and fifty-seven cases with superficial hemangioma were recruited. The overall effectiveness rate was 91.17%. Female patients respond better than male, the difference was statistically significant (p < 0.001). Lesions at different part of the body respond differently to the treatment with lesions on extremities show the best result. The response rate does not increase with time of treatments. The most common side-effects were pigment changes and skin atrophy, which usually resolve spontaneously and disappear completely in a few months. Conclusions: Our experience confirmed the satisfactory clinical efficacy and safety of the 595 nm tunable pulse dye laser in the treatment of childhood superficial hemangioma.

Photo-annealing effect of gamma-irradiated erbium-doped fibre by femtosecond pulsed laser

In this work, a photo-annealing effect of gamma-irradiated erbium-doped glass fibre is investigated. Two commercial erbium-doped fibres (EDFs) with different doping concentrations were sealed inside a chamber with a cobalt-60 gamma source for 6 h to give an accumulated dose of 3.18 kGy. A tunable femtosecond pulsed laser with a repetition rate of 80 MHz was then used to pump EDF to generate 1550 nm fluorescence and green up-conversion emission, resulting in the annealing effect of the gamma-irradiated EDF. The fluorescence power of gamma-irradiated EDF with a moderate level of doping was almost returned to the initial state by photo-annealing, unlike that of a heavily doped EDF. This finding may facilitate the development of anti-irradiated superfluorescence fibre source for space navigation.

Ca3La2(BO3)4 crystal: a new candidate host material for the ytterbium ion

A disordered laser crystal Yb3+-doped Ca3La2(BO3)4 crystal was grown by the Czochralski technique. The characterized room temperature polarized spectra, re-absorption possibility and laser performance showed that this crystal should be a promising gain material, not only suitable for diode pumping, but also a good candidate for the generation of tunable and short pulse lasers. End pumped by a diode laser at 976 nm in plano-concave and plano–plano cavity, a 3.65 W output power with a slope efficiency of 65% was achieved by using a c-cut Yb3+:Ca3La2(BO3)4 crystal. The output laser wavelength shifted from 1042 to 1062 nm.

Tunable 1.6–2 μm near infrared few-cycle pulse generation by filamentation

We present results on tunable few-cycle laser pulses generated in the near infrared region obtained by filamentation in a krypton cell combined with group velocity dispersion compensation in fused silica. We obtain a spectral broadening of a factor ∼2–3 over the entire spectral domain studied. The central wavelength is tuned from 1.6 μm to 2 μm via an optical parametric amplification source. In optimum experimental conditions, where the input central wavelength is set to 1.7 μm, 1.8 μm, and 1.9 μm, the incident power to the gas cell exceeded the critical power of Krypton by a factor of ∼4 and the achieved spectral broadening covered ∼300 nm. Using group velocity compensation in bulk fused silica, we obtain near infrared output pulses as short as 2–3 optical cycles with 200 μJ energy per pulse. This near infrared filamentation tunable few-cycle pulse source is an important achievement for strong field physics applications such as attoscience, where wavelength scaling has an important effect.

Nanoscale infrared (IR) spectroscopy and imaging of structural lipids in human stratum corneum using an atomic force microscope to directly detect absorbed light from a tunable IR laser source

An atomic force microscope (AFM) and a tunable infrared (IR) laser source have been combined in a single instrument (AFM-IR) capable of producing ~200-nm spatial resolution IR spectra and absorption images. This new capability enables IR spectroscopic characterization of human stratum corneum at unprecendented levels. Samples of normal and delipidized stratum corneum were embedded, cross-sectioned and mounted on ZnSe prisms. A pulsed tunable IR laser source produces thermomechanical expansion upon absorption, which is detected through excitation of contact resonance modes in the AFM cantilever. In addition to reducing the total lipid content, the delipidization process damages the stratum corneum morphological structure. The delipidized stratum corneum shows substantially less long-chain CH2 -stretching IR absorption band intensity than normal skin. AFM-IR images that compare absorbances at 2930/cm (lipid) and 3290/cm (keratin) suggest that regions of higher lipid concentration are located at the perimeter of corneocytes in the normal stratum corneum.

UV Photodissociation Action Spectroscopy of Haloanilinium Ions in a Linear Quadrupole Ion Trap Mass Spectrometer

UV-vis photodissociation action spectroscopy is becoming increasingly prevalent because of advances in, and commercial availability of, ion trapping technologies and tunable laser sources. This study outlines in detail an instrumental arrangement, combining a commercial ion-trap mass spectrometer and tunable nanosecond pulsed laser source, for performing fully automated photodissociation action spectroscopy on gas-phase ions. The components of the instrumentation are outlined, including the optical and electronic interfacing, in addition to the control software for automating the experiment and performing online analysis of the spectra. To demonstrate the utility of this ensemble, the photodissociation action spectra of 4-chloroanilinium, 4-bromoanilinium, and 4-iodoanilinium cations are presented and discussed. Multiple photoproducts are detected in each case and the photoproduct yields are followed as a function of laser wavelength. It is shown that the wavelength-dependent partitioning of the halide loss, H loss, and NH3 loss channels can be broadly rationalized in terms of the relative carbon-halide bond dissociation energies and processes of energy redistribution. The photodissociation action spectrum of (phenyl)Ag2 (+) is compared with a literature spectrum as a further benchmark.

Abstract 720: A validation study on photoacoustics imaging of fluorescent pyroporphysome in vivo.

Abstract Photoacoustics (PA) is a hybrid in vivo imaging modality that combines the temporal resolution of optics, and low acoustic scattering and high spatial resolution of micro-ultrasound. This innovation can discern optical absorption of endogenous and exogenous contrast agent(s) in the tumor micro-environment. This advancement is made possible by precise control of optical wavelength using a tunable pulsed laser, ranging from 680-970nm. In this study, we demonstrate fluorescent pyroporphysome, a nanoparticle, to be a photoacoustic contrast agent by which we can monitor its accumulation locally within the tumor. Approach: Co-registered ultrasound (anatomical) and PA imaging of subcutaneous tumors was accomplished with a LZ250 21 MHz transducer on the Vevo® LAZR system (FUJIFILM VisualSonics, Inc.). Mammary tumors were generated by implanting from MDA-MB-231H2N cell line under the skin line. Pyroporphysomes (120 nm in size) were administered by tail vein at a dose of 300 nmoles. Multiwavelength photoacoustic scans were acquired and quantified over 24 hours using Vevo Spectro (FUJIFILM VisualSonics, Inc.), an ensuite absorbance spectrum quantification tool. Cri Maestro (Quorum Technologies, Inc.) was used for concurrent whole body fluorescence imaging. Results: Multi-wavelength analyses identified an in vivo PA absorbance of 680 nm to pyroporphysome. Earliest detection was at 20 minutes post bolus in the tumor and PA signal for pyroporphysomes persisted at 24 h. Signal accumulation is supported by a 22 fold change in signal intensity per 3D volume (3.8% post bolus vs 87% at 24h). Fluorescence analyses validate this accumulation in the tumor. Taken together, photoacoustic imaging identifies pyroporphysome as a bimodal contrast agent. Additional evidence includes a shift in signal localization in the PA scans wherein pyroporphysomes were first detected at the tumor periphery (&amp;lt;1mm below the skin line), and as deep as 2mm towards the tumor core at 24 hours. In conclusion, data herein presents photoacoustic imaging as the next generation imaging modality for concurrent molecular and anatomical information to better understand mechanistic changes in the tumor microenvironment. Citation Format: Minalini Lakshman, James Bu, Azusa Maeda, Gang Zheng, Andrew Needles, Catherine Theodoropoulos, Ralph Da Costa. A validation study on photoacoustics imaging of fluorescent pyroporphysome in vivo. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 720. doi:10.1158/1538-7445.AM2013-720

Observation of even-parity autoionization states of uranium by three-colour photoionization optogalvanic spectroscopy in U–Ne hollow cathode discharges

Three-colour three-step photoionization spectroscopy of uranium has been performed in a U–Ne hollow cathode discharge tube by temporally resolving three-colour photoionization optogalvanic (PIOG) signal from the normal optogalvanic (OG) signal using three tunable pulsed dye lasers. U–Ne hollow cathode discharge tube has been used as a source of uranium atomic vapours and photoionization detector. Using this technique, photoionization spectra of uranium have been investigated systematically in the energy region 52,150–52,590cm−1, through three different excitation pathways, originating from its ground state, 0cm−1(5Lo6). By analysing the three-colour photoionization spectra sixty new even-parity autoionization resonances of uranium have been identified and their probable total angular momentum (J) values have been assigned according to the J-momentum selection rule. The J-value of five autoionization resonances, which have been observed either through all three excitation pathways or through two different excitation pathways where J-value of the second excited levels differs by two, has been assigned uniquely.