Tunable UV Source Research Articles

High-efficiency narrow-bandwidth KTP optical parametric oscillator for kHz-MHz planar laser-induced fluorescence.

The electronic excitation of key combustion species or flow tagging of chemical species requires a narrowband tunable UV source. In this work, a potassium titanyl phosphate (KTP) burst-mode optical parametric oscillator (OPO) pumped by a 532 nm laser is developed to generate a spectrally narrow signal and an idler output with 1.48 ± 0.19 cm-1 bandwidth without the need for injection seeding. The idler (1410-1550 nm range) is further mixed with 355 or 266 nm to generate 284 or 226 nm for OH or NO planar laser-induced fluorescence (PLIF), respectively, with up to 1.9% conversion efficiency from 1064 nm to the UV. MHz-rate burst profiles are reported, and OH and NO PLIF are demonstrated in a rotating detonation combustor at rates up to 200 kHz.

Tunable UV source based on an LED-pumped cavity-dumped Cr:LiSAF laser.

We developed a light-emitting diode (LED)-pumped Cr:LiSAF laser operating in Q-switched and cavity-dumped regimes. The laser produces 1.1 mJ pulses with a pulse duration of 8.5 ns at a repetition rate of 10 Hz on a broad spectrum centered at 840 nm with a full width at half maximum of 23 nm. After frequency tripling in two cascaded LBO crystals, we obtained 7 ns pulses with an energy of 13 µJ at 280 nm and with a spectral width of 0.5 nm, limited by the spectral acceptance of the phase matching process. By rotating both LBO crystals, UV emission is tuned from 276 nm to 284 nm taking advantage of the broad infrared spectrum of the Cr:LiSAF laser.

Identification of the shallow donor state in Sb doped ZnO by photoluminescence excitation spectroscopy

Photoluminescence excitation (PLE) spectroscopy was used to investigate the optical properties of the recently discovered 3364.3 meV antimony-related donor bound exciton (D0X) in zinc oxide. By suitable control of the growth conditions, we achieved samples in which the Sb-related donor emission was the dominant near-bandgap luminescence feature. Resonant excitation using a tunable UV source enabled the observation of the two electron transitions of the donor bound exciton, enabling the direct determination of the binding energy of the Sb donor at 42.2±0.5 meV, the lowest value yet reported for a donor in this material. The two electron transitions exhibit an unusual blue shift with increasing temperature, which is explained in terms of thermalization of excited states of the D0X initial state. The D0X excited states were probed by PLE and follow the trends of conventional shallow group III donors such as Al, Ga, and In.

Atmospheric pressure photoionization study of post-translational modifications: The case of palmitoylation

In this work, atmospheric pressure photoionization was investigated for use in characterizing protein palmitoylation, which is a major post-translational modification of membrane proteins. The study focused on native and palmitoylated peptides originating from plasma membrane proteolipids, such as tetraspanins CD9 and CD151. Mass spectrometry experiments were performed using synchrotron radiation as a tunable UV source that provides optimal energy for photoionization (SR-APPI). In the positive ion mode, intense fragment ions corresponding to a, b, c and y ions were observed. Interestingly, these fragment ions conserved the palmitoyl modification, thus allowing for unambiguous structural characterization of the palmitoylated peptides. In-source fragmentation under APPI conditions offers a unique complement to conventional methods such as MS/MS, and the results demonstrate that APPI is a versatile and promising technique for the in-source characterization of post-translational modifications and top-down proteomics of membrane proteins.

All Solid-State High-Efficiency Tunable UV Source for Airborne or Satellite-Based Ozone DIAL Systems

We designed, built, and tested two laboratory prototype nanosecond UV sources for airborne or satellite-based ozone differential absorption lidar (DIAL) remote-sensing systems. Our prototypes use a 532-nm second-harmonic pulse from a Q-switched injection-seeded Nd:YAG laser to pump an optical parametric oscillator (OPO) that generates a tunable signal wavelength near 803 nm. The OPO signal is mixed with additional 532 nm light either inside the OPO cavity, or in a subsequent sum-frequency generation (SFG) stage, to generate 10-ns pulses at 320-nm. Our system designs result from an integrated, iterative approach where operating parameters including the pump-beam's spatial profile, the second harmonic generation efficiency, the OPO's cavity geometry, output coupling, crystal lengths, and the length of the SFG crystals, are all determined from numerical modeling. By using this approach, we obtained 320 nm pulse energies approaching 200 mJ with overall optical conversion efficiency-from 1064 to 320 nm-exceeding 20%. To optimize efficiency, we incorporate three important design characteristics: a pump beam having a high-quality flat-topped spatial profile, an image-rotating non-planar ring-cavity OPO capable of generating high-quality large-diameter flat-topped beams, and pulse injection seeding of the OPO to achieve near-zero cavity buildup time to enhance the efficiency of sum-frequency mining. We believe additional optimization of our designs may eventually yield UV pulse energies approaching 300 mJ with optical conversion efficiencies comparable to those of our current systems.

Two-step photoconductivity: determination of impurity levels of Er3+ relative to the host bands of Gd2O3

A two-step photoconductivity measurement in Gd2O3:Er3+ is used to determine the location of the f11 energy levels of Er3+ with respect to the host bands of Gd2O3 . Photoconductivity (PC) experiments were performed with both a tunable UV source and with 488nm Ar+ excitation, as well as in the presence of both light sources. Using only the UV source, PC features with onsets at 240 and 340nm are identified as direct band gap excitation and two-step excitation involving excited state absorption on Er3+, respectively; the latter is confirmed by its quadratic dependence on intensity. Under simultaneous Ar+ excitation, which enhances the population of the metastable 4S3/2 Er3+ excited state population, the PC feature with a 340nm onset increases dramatically and its magnitude depends linearly on both UV and Ar+ laser intensity, supporting its interpretation as resulting from excited state absorption form the 4S3/2 metastable Er3+ excited state.The 340nm onset of the signal allows one to place the 4I15/2 ground state at 0.7±0.2eV below the top of the valence band. The lowest 4f105d level then lies close to the bottom of the conduction band and its overlap with the conduction band is thought to enhance the second step in the photoionization process.

Tunable UV-source based on frequency-doubled reddiode laser oscillator-amplifier system

Tunable UV radiation with an output power of 30 µW is generated in the range from 334 to 340 nm by single-pass frequency doubling of 400 mW of diode laser radiation in an LiIO3 crystal. The diode source is an external-cavity AlGaInP laser (668-680 nm), which is amplified in a tapered semiconductor amplifier.

State-to-state dissociation of SO 2 in C̃ 1B 2: Rotational distributions of the fragment SO

The predissociation of SO 2 in the electronically excited C̃ 1B 2 state is studied in a state-to-state experiment. Using a frequency-doubled dye laser, the photodissociation of jet-cooled SO 2 via single rovibrational levels is possible. A second tunable UV source is applied to detect the population of the molecular fragment SO by means of (1+1) REMPI–TOF technique. The observed rotational population distributions of SO(X 3Σ −, v″=1, 2) for dissociation closely above the respective thresholds are in good agreement with simulations from phase-space theory (PST). With increasing excess energy, deviations between experiment and PST model become significant: The spin component 3P 2 of the fragment O is highly populated compared to the other two components of 3P, we observe population differences of the three spin components of SO in its ground state 3Σ. For small angular momenta ( J<5) of the dissociating state of SO 2 the rotational distributions of SO are distinctively structured. But they approach with increasing J the distributions according to the PST model. Simulations of such structures with a Franck–Condon mapping of the bending vibration of SO 2 onto the rotation of the fragment SO were not completely convincing.

Rotationally resolved spectroscopy of deuterated fluorene and the fluorene—argon van der Waals complex

With a single frequency tunable UV source in combination with a collimated molecular beam, rovibronic fluorescence spectra were obtained for fully deuterated fluorene and its van der Waals complex with argon. The O 0 0 vibronic band in both molecules was assigned and molecular constants derived. The argon atom in the complex lies above the middle ring of the fluorene molecule. It is shown that substantial zero-point motions are present in the complex, hindering a precise determination of the effective structure.

ChemInform Abstract: NEAR‐UV SPECTRA WITH FULLY RESOLVED ROTATIONAL STRUCTURE OF NAPHTHALENE AND PERDEUTERATED NAPHTHALENE

Abstract The combination of a single-frequency, tunable uv source with a well-collimated supersonic molecular beam and sensitive fluorescence detection has been used to obtain spectra with rovibronic resolution for some large organic molecules. The results of analysis of the 000 and 8 01 vibronic bands of the 1 B 3u ← 1 A g electronic transition for naphthalene and naphthalene-dg are presented. The obtained spectra are assigned using a rigid asymmetric rotor Hamiltonian and the structure in both the ground and electronically excited states is determined. The rotational temperature of the molecules cooled in the beam has been determined. The influence of the nuclear spin statistics on the line intensities is observed and discussed.

Near-uv spectra with fully resolved rotational structure of naphthalene and perdeuterated naphthalene

The combination of a single-frequency, tunable uv source with a well-collimated supersonic molecular beam and sensitive fluorescence detection has been used to obtain spectra with rovibronic resolution for some large organic molecules. The results of analysis of the 0 0 0 and 8 0 1 vibronic bands of the 1B 3u ← 1A g electronic transition for naphthalene and naphthalene-d g are presented. The obtained spectra are assigned using a rigid asymmetric rotor Hamiltonian and the structure in both the ground and electronically excited states is determined. The rotational temperature of the molecules cooled in the beam has been determined. The influence of the nuclear spin statistics on the line intensities is observed and discussed.

Continuously Tunable Pulsed Ultraviolet Light Source

A technique is described for producing a continuously tunable uv source using the broadband emission from a dye laser as input to a rotatable KDP crystal. A theoretical model is developed based on mixing of emission band components which are spaced equidistant and symmetrically about the part of line that corresponds to maximum SHG (Deltak = 0). This model agrees well with the observed spectral line narrowing, relatively high experimental conversion efficiency, and experimental tuning curve.