Power Tunable Laser Research Articles

Improvement in measuring losses by interferometric technique for glass waveguides produced by femtosecond laser writing

This study describes a straightforward and non-destructive interferometric technique for measuring the propagation loss in single-mode optical glass waveguides by exploiting a Fabry–Perot cavity effect. The experiment involves coupling a powerful tunable laser source to a single-mode waveguide that is being tested, then using a detector to analyze the transmission fringes of that source after coating the glass end facets with highly reflective coating. Our first experiment, which used a 22.4-mm-long fabricated waveguide on Non-Iox Gorilla glass to demonstrate the technique, resulted in a propagation loss of 0.49 dB/cm at a transmitting wavelength of about 1575 nm, which is completely consistent with the value obtained by a conventional characterization method. The measurement procedure is also independent from the coupling losses, making the characterization easier and reliable after the manufacturing just with a reversible deposition process on the sample under testing.

Li+ aided self-activated [formula omitted] phosphors for efficient dual-mode emission and temperature sensing application

For the first time, lanthanide co-doped self-activated Ca9Y1−x−yErxYby(VO4)7 phosphors have been investigated for bearing dual-mode emission: downshifting and upconversion emission behavior. The Ca9Y1−x−yErxYby(VO4)7 phosphor, under 379 nm excitation evinces two bright green emission peaks at 525 nm and 553 nm, which corresponds to H11/22,S3/24→I15/24 transitions of Er3+ ion, this transition is sensitized by an efficient energy transfer from the (VO4)3− group to Er3+ ions. Irradiated with a 980 nm power tunable laser, it shows strong green and comparatively weak red emissions bands. The upconversion emission can be enhanced enormously with the introduction of Li+ ions in the optimized Ca9Y0.847Er0.003Yb0.15(VO4)7 phosphor. Furthermore, utilizing the well-known fluorescence intensity ratio (FIR) technique, optimized Ca9Y0.647Li0.20Er0.003Yb0.15(VO4)7 phosphor has been explored for optical temperature sensors also. The maximum absolute sensitivity and relative sensitivity are obtained to be 0.0125 K−1 at 513 K and 0.012 K−1 at 300 K, respectively. The acquired result reveals that the phosphor Ca9Y0.647Li0.20Er0.003Yb0.15(VO4)7 can be a worthy material for temperature sensing application.

High power ultralow-intensity noise continuous wave laser tunable from orange to red.

We report here on the development of a multi-Watt power tunable single frequency ultra-low noise laser system emitting around 620 nm. More than 5 W of output power is obtained between 616.5 nm and 630.8 nm using sum frequency generation of 1050 nm and 1550 nm tunable laser sources in a periodic poled lithium niobate crystal. The tunability is achieved through temperature and channel shift, and only limited by the crystal characteristics. An output power of 10.1 W and an optical-optical efficiency of 45% are reached at 624.5 nm. The relative intensity noise properties of the conversion process have been experimentally investigated in different configurations showing excellent agreement with the analytical prediction.

Autonomous Differential Absorption Laser Device for Remote Sensing of Atmospheric Greenhouse Gases

A ground-based, integrated path, differential absorption (IPDA) light detection device capable of measuring multiple greenhouse gas (GHG) species in the atmosphere is presented. The device was developed to monitor greenhouse gas concentrations in small-scale areas with high emission activities. It is equipped with two low optical power tunable diode lasers in the near-infrared spectral range for the atmospheric detection of carbon dioxide, methane, and water vapors (CO2, CH4 and H2O). The device was tested with measurements of background concentrations of CO2 and CH4 in the atmosphere (Crete, Greece). Accuracies in the measurement retrievals of CO2 and CH4 were estimated at 5 ppm (1.2%) and 50 ppb (2.6%), respectively. A method that exploits the intensity of the recorded H2O absorption line in combination with weather measurements (water vapor pressure, temperature, and atmospheric pressure) to calculate the GHG concentrations is proposed. The method eliminates the requirement for measuring the range of the laser beam propagation. Accuracy in the measurement of CH4 using the H2O absorption line is estimated at 90 ppb (4.8%). The values calculated by the proposed method are in agreement with those obtained from the differential absorption LiDAR equation (DIAL).

High power tunable multiwavelength random fiber laser at 1.3 μm waveband.

Multiwavelength fiber lasers, especially those operating at optical communication wavebands such as 1.3 μm and 1.5 μm wavebands, have huge demands in wavelength division multiplexing communications. In the past decade, multiwavelength fiber lasers operating at 1.5 μm waveband have been widely reported. Nevertheless, 1.3 μm waveband multiwavelength fiber laser is rarely studied due to the lack of proper gain mechanism. Random fiber laser (RFL), owing to its good temporal stability and flexible wavelength tunability, is a great candidate for multiwavelength generation. Here, we reported high power multiwavelength generation at 1.3 μm waveband in RFL for the first time. At first, we employed a section of 10 km G655C fiber to provide Raman gains, as a result of which, 1.07 W multiwavelength generation at 1.3 μm waveband with an optical to signal noise ratio of ∼33 dB is demonstrated. By tuning the pump wavelength from 1055 nm to 1070 nm, tunable multiwavelength output covering the range of 1300-1330 nm can be achieved. Furtherly, we realized 4.67 W multiwavelength generation at 1.3 μm waveband by shortening the fiber length to 4 km. To the best of our knowledge, this is the highest output power ever reported for multiwavelength fiber lasers.

High power, high SMSR and wide tuning range silicon micro-ring tunable laser.

An external cavity tunable laser, which is based on a silicon hybrid micro-ring resonator, is demonstrated. The heat isolate grooves around the rings effectively cuts off temperature crosstalk. Experimental results have shown that the output power of this device can reach 15.5dBm, with a linewidth less than 130 kHz. The tuning range is more than 57nm in C-band with 60 dB side mode suppression ratio (SMSR).

An optical parametric chirped-pulse amplifier for seeding high repetition rate free-electron lasers

High repetition rate free-electron lasers (FEL), producing highly intense extreme ultraviolet and x-ray pulses, require new high power tunable femtosecond lasers for FEL seeding and FEL pump-probe experiments. A tunable, 112 W (burst mode) optical parametric chirped-pulse amplifier (OPCPA) is demonstrated with center frequencies ranging from 720–900 nm, pulse energies up to 1.12 mJ and a pulse duration of 30 fs at a repetition rate of 100 kHz. Since the power scalability of this OPCPA is limited by the OPCPA-pump amplifier, we also demonstrate a 6.7–13.7 kW (burst mode) thin-disk OPCPA-pump amplifier, increasing the possible OPCPA output power to many hundreds of watts. Furthermore, third and fourth harmonic generation experiments are performed and the results are used to simulate a seeded FEL with high-gain harmonic generation.

Growth and Spectral Assessment of Yb3+-Doped KBaGd(MoO4)3 Crystal: A Candidate for Ultrashort Pulse and Tunable Lasers

In order to explore new more powerful ultrashort pulse laser and tunable laser for diode-pumping, this paper reports the growth and spectral assessment of Yb3+-doped KBaGd(MoO4)3 crystal. An Yb3+:KBaGd(MoO4)3 crystal with dimensions of 50×40×9 mm3 was grown by the TSSG method from the K2Mo2O7 flux. The investigated spectral properties indicated that Yb3+:KBaGd(MoO4)3 crystal exhibits broad absorption and emission bands, except the large emission and gain cross-sections. This feature of the broad absorption and emission bands is not only suitable for the diode pumping, but also for the production of ultrashort pulses and tunability. Therefore, Yb3+:KBaGd(MoO4)3 crystal can be regarded as a candidate for the ultrashort pulse and tunable lasers.

Simultaneous detection of trace gases using multiplexed tunable diode lasers and a photoacoustic cell containing a cantilever microphone

We report what we believe to be a novel demonstration of simultaneous detection of multiple trace gases by near-IR tunable diode laser photoacoustic spectroscopy using a cell containing a cantilever microphone. Simultaneous detection of carbon monoxide (CO), ethyne (C2H2), methane (CH4) and combined carbon monoxide/carbon dioxide (CO+CO2) in nitrogen-based gas mixtures was achieved by modulation frequency division multiplexing the outputs of four near-IR tunable diode lasers. Normalized noise-equivalent absorption coefficients of 3.4×10−9, 3.6×10−9 and 1.4×10−9 cm−1 W Hz−1/2 were obtained for the simultaneous detection of CO, C2H2 and CH4 at atmospheric pressure. These corresponded to noise-equivalent detection limits of 249.6 ppmv (CO), 1.5 ppmv (C2H2) and 293.7 ppmv (CH4) respectively over a measurement period of 2.6 s at the relevant laser power. The performance of the system was not influenced by the number of lasers deployed, the main source of noise arising from ambient acoustic effects. The results confirm that small-volume photoacoustic cells can be used with low optical power tunable diode lasers for rapid simultaneous detection of trace gases with high sensitivity and specificity.

TU‐C‐220‐06: Photoacoustic Imaging of Deep Targets in the Breast Using a Multi‐Channel 2D Array Transducer

Purpose: To pave the road toward successful application of photoacoustic imaging (PAI) to breast cancer, an initial evaluation of a home fabricated PAI system designed deliberately to achieve high sensitivity for the detection and characterization of vascular anomalies in the breast in the mammographic geometry was completed. Method and Materials: Signal detection from deep breast was achieved by a broadband 2D PVDF planar array that has a round shape with one side trimmed straight to improve fit near the chest wall. This array has 572 active elements and a −6dB bandwidth of 0.6–1.7 MHz. The low frequency of the array enhances imaging depth and increases the size of vascular collections displayed without edge enhancement. The photoacoustic signals from all the elements go through low noise preamplifiers in the probe that are very close to the array elements for optimized noise control. Driven by 20 independent on‐probe signal processing channels, imaging with both high sensitivity and good speed was achieved. Results: According to our measurements, the end of cable sensitivity was 2.5mV/Pa. Without averaging, the minimum detectable pressure was 80 Pa. Based on the measurements of a point object at different distances from the surface of the array, the lateral resolution of the system ranges from 2.9 mm to 4.2mm and axial resolution ranges from 1.9 mm to 3.7 mm within the distance of 60 mm. To evaluate the imaging depth of this system, artificial vessels embedded deeply in ex vivo breasts harvested from fresh cadavers were imaged. Using near‐infrared laser light with incident energy density within the ANSI safety limit, imaging depth of up to 49 mm in human breasts was achieved. To validate the multi‐modality imaging possibility, PAI images of a compressed breast containing a catheter balloon filled with blood was coregistered with ultrasound images acquired from the same specimen. PAI, based on the intrinsic tissue optical contrast, successfully presented some breast tissue features, including the interfaces on both sides of the skin, the connective tissue sheet in subcutaneous fat, and the lobar capsule. Conclusions: The current imaging speed of this system is adequate for laboratory research and in vivo human studies with small numbers of cooperative volunteers. With a high power tunable laser working on multiple wavelengths, this system might contribute to 3D noninvasive imaging of morphological and physiological tissue features throughout the breast.

A new grating tuning compound unstable resonator

A proposal of new grating tuning compound unstable resonator is presented. This new type of unstable resonator is profitable for generating single transverse mode, high energy, high-average power tunable laser radiation from TEA CO 2 laser and other gas lasers.

High output power tunable twin-guide laser diodes with improved lateral current injection structure

Tunable twin-guide laser diodes with improved lateral current injection structure and high output power are reported. By optimising the doping profile of the n-InP layer laterally surrounding the buried stripe, inherent leakage currents are effectively minimised. Thereby, the carrier injection efficiency of the laser diode is significantly increased and high output powers of up to 24 and 3.3 mW are obtained at operation temperatures of 20 and 80°C, respectively.

Thermal stability, spectra and laser properties of Yb:lead-zinc-lanthanum-tel lurite glasses

A series of new glasses of 70TeO22-(20-x) ZnO-xPbO-5La22O33-25K22O-25Na22O (x=0,5,10,15, 20mol %) doped with Yb22O33 is presented. Thermal stability, spectra and laser properties of Yb3+3+ ions have been measured. It has been found that the glass with x=15 has a good thermal s tability ((Txx-Tgg)>195℃), high stimulated emission cross -section of 125pm22 for the 22F5/25/2 →22F7/27/2 transition and a long fluorescence lifetime of 094ms and a broad fluorescence effective linewidth of 72nm. From the viewpoint of good potential laser parameters, it is desirab le to have high-average power and short pulse tunable laser, which can be achie ved by doping with Yb22O33.

Optical gain on the I2 (B3Πo+→X3Σg+) system produced by a visible wavelength diode laser

We report the results of a measurement of subdoppler gain profiles in molecular iodine produced by a low power tunable diode laser. Using a sensitive, two beam detection method, we have measured absorptions and amplifications that are only a few parts in 104. Amplification was observed for pump laser powers of only 200 μW, and the optical gain observed varied linearly with pump power. Comparisons with a simple, steady-state model are also discussed.

Emission Spectra Inside the Ammonia s-Multiplets Pumped by a Line-Narrowed Tunable CO2 Laser

By using a line narrowed high power tunable laser we have analysed the FIR emission spectrum inside some , compact sQ, sR k-multiplets. Jumps between adjacent k-systems are observed , although tunable emissions of dominant lines are produced. The more favourable gain overlap of the K Raman lines in the fundamental vibrational level induces an off-resonance dominance of this process respect to the standard Raman scattering in the excited vibrational level. The AC Stark splitting has been also observed when the CO2 laser is posed in resonance with the absorption lines.

High power tunable UV laser radiation produced by second-harmonic generation in β-BaB2O4

High power tunable UV laser radiation from 2750Å to 3200Å has been obtained by second-harmonic generation in a β-BaB2O4 crystal. A maximum frequency doubling efficiency of 41% and a UV output power of 3.7MW have been obtained.

Sensitive quantum state selective detection of H2O and D2O by (2+1)-resonance enhanced multiphoton ionization

The first observation of (2+1)-REMPI of H2O and D2O is reported. With the use of a high power tunable excimer laser radiating at 248 nm, the H2O and D2O molecules are ionized after resonant two-photon absorption into the predissociated C̃ 1B1 state. The clearly observable peaks in the (2+1)-REMPI spectra are all identified and can be used for sensitive state selective detection. Parent molecular fluorescence excitation spectra (C̃ 1B1→Ã 1B1) were remeasured over an increased spectral range, and are remarkably the same as the (2+1)-REMPI spectra. Furthermore the OH/OD (A 2Σ+, v′=0→X 2Π, v″=0) photofragment fluorescence excitation spectra were measured, and these spectra do not show any nonresonant background as stated before. Additional fluorescence bands starting from the vibrationally excited A 2Σ+, v′=1 state were observed. Simulation of the observed REMPI and fluorescence excitation spectra yields the branching ratios for the predissociation, ionization, and fluorescence processes.

Lidar measurements of ozone vertical profiles

Remote measurements of trace constituents using an active technique such as lidar have been made possible for the rapid development of powerful tunable laser sources. This paper, originally presented at the OSA Topical Meeting on Optical Remote Sensing of the Atmosphere, in January 1985, illustrates the differential absorption lidar technique used for the measurement of the ozone vertical distribution in the troposphere and the atmosphere.

The S1(n,π*) states of cyclopentanone and cyclobutanone in a supersonic nozzle beam

Fluorescence excitation spectra of cyclopentanone and cyclobutanone have been observed for their (n,π*) transition in a pulsed supersonic nozzle beam using a high power tunable laser. A drastic reduction of hot bands has been attained, making it possible to discuss the vibronic assignments in more detail than the previous works. The C=O out-of-plane wagging mode was found to be active for both molecules. The ring twisting and flapping in cyclopentanone and the ring puckering in cyclobutanone were also active. The molecules are pyramidally distorted in the excited states with double minimum potentials in the out-of-plane displacement coordinates. The barrier to inversion (V) and the C=O out-of-plane angle at the potential minimum (θm) have been determined for the S1(n,π*) state; V=680±17 cm−1 and θm=34° for cyclopentanone, and V=1850±50 cm−1 and θm=42° for cyclobutanone. The puckering mode (ν20′) of cyclobutanone was also found to have a double minimum potential with V=16.9 cm−1. The rotational envelope of each vibronic band has been analyzed on the basis of a computer simulation for an asymmetric top molecule. In contrast with formaldehyde, the A-type (parallel) component, as well as the B-type, was shown to be important in these cyclic ketones. The mechanism of the vibronic intensity borrowing is discussed on the basis of the band-type considerations.

Ir hole burning and line shape of matrix-isolated 1,2-difluoro-ethane with tunable diode lasers. part 2

Some recent results of IR hole burning experiments of CH2F-CH2F (trans conformation), matrix isolated in Ar and Kr are reported. A low power tunable diode laser was used for burning holes into the absorption profile as well as for recording the spectra. Temperature dependence of the hole width, closely related to the homogeneous width was determined, from which a vibrational life time of 5̃ ns at 0 K can be estimated. Effects of polarized laser radiation are demonstrated.