Laser Output Wavelength Research Articles

Full-field phase measurement by wavelength-tuning interferometry in the C-band

Fluctuations in the output intensity and wavelength of an external cavity diode laser can introduce significant error to wavelength-tuned interferometric measurement. However, a robust phase-retrieval algorithm can compensate for these nonlinearities. Employing an inexpensive phosphor-coated charge-coupled device camera sensitive to C-band infrared, full-field interferometric phase retrieval utilizing wavelength tuning of a 1555 nm external cavity diode laser is reported. Phase measurement of a tilted mirror is presented with an estimated accuracy within 7 nm.

Stable single frequency and single polarization DFB fiber lasers operated at 1053 nm

Stable single-frequency and single-polarization distributed-feedback (DFB) fiber laser was realized by giving a pressure on the phase shift region of the fiber grating. The output wavelength of the DFB fiber laser is 1053 nm. When the pump power of 980 nm laser diode is 100 and 254 mW, the output power can reach 8.3 and 37.1 mW and the polarization extinction ratio was 26 and 20 dB, respectively. After chopped by Acousto-optic modulator (0.3 Hz), the pulse peak value variance is 4.65%(peak to peak) and 1.098% (RMS) for 31 min.

Real-time tunability of chip-based light source enabled by microfluidic mixing

We demonstrate real-time tunability of a chip-based liquid light source enabled by microfluidic mixing. The mixer and light source are fabricated in SU-8 which is suitable for integration in SU-8-based laboratory-on-a-chip microsystems. The tunability of the light source is achieved by changing the concentration of rhodamine 6G dye inside two integrated vertical resonators, since both the refractive index and the gain profile are influenced by the dye concentration. The effect on the refractive index and the gain profile of rhodamine 6G in ethanol is investigated and the continuous tuning of the laser output wavelength is demonstrated using an ethanolic rhodamine 6G solution of 2×10−2mol∕l mixed with pure ethanol. This yields rhodamine 6G concentrations from 5×10−3 to 1.5×10−2mol∕l inside the laser resonators and a wavelength change of 10 nm with a response time of 110 s.

Spacing-adjustable multi-wavelength source from a stimulated Brillouin scattering assisted erbium-doped fiber laser

We demonstrate room-temperature operation of a spacing-adjustable multi-wavelength erbium-doped fiber laser using stimulated Brillouin scattering. With the use of an intra-cavity birefringent loop mirror filter, the laser output wavelengths can be well defined without applying an external Brillouin pump. By adjusting the comb spacing of the filter, a wide range of mode spacings can be obtained to support the oscillations of up to 49 output wavelengths.

Intracavity measurement of liquid crystal layer thickness by wavelength tuning of an external cavity laser diode

The gap of a planar-aligned liquid crystal (LC) cell is measured by a novel method: Monitoring the change in output wavelength of an external-cavity diode laser by varying the voltage driving the LC cell placed in the laser cavity. This method is particularly suitable for measurement of LC cells of small phase retardation. Measurement errors of +/-0.5 % and +/-0.6 % for 9.6-microm and 4.25-microm cells with phase retardations of 1.63 microm and 0.20 microm respectively are demonstrated.

Comparison of spectroscopic parameters of 15 at% Yb: YAlO 3 and 15 at% Yb: Y 3Al 5O 12

Yb: YAlO 3 (YAP) (15 at%) and Yb: Y 3Al 5O 12 (YAG)(15 at%) have been grown using the Czochralski method. Their absorption and fluorescence spectra were measured at room temperature and important spectroscopic parameters were calculated. Through the comparison of spectroscopic parameters of Yb:YAP and Yb: YAG, all results indicate that 15 at % Yb:YAP crystal is a potential candidate used for compact, efficient thin chip lasers when the laser output wavelength is 1012 or 1038 nm.

Yb3+-Doped Four-Wavelength Double Clad Laser

A novel Yb3+-doped four-wavelength double clad fibre laser basedon a Fabry-Perot filter, and pumped by a 976 nm laser diode ispresented. Its output laser wavelengths are 1085, 1090, 1095 and1010 nm, respectively. The laser exhibits 0.32 nm line-width, 1.5 W laseroutput power, 40 dB signal-to-noise ratio and 66% slope efficiency.

Tunable multiwavelength distributed-feedback zirconia waveguide lasers.

Simultaneous tuning of multiple-output wavelengths was achieved in Rhodamine 6G-doped distributed-feedback zirconia waveguide lasers. As many as four separate output wavelengths were observed for a planar zirconia waveguide of 2.2-microm thickness. The laser output wavelengths corresponded to the propagation modes allowed in the planar waveguide. Continuous tuning by variation of the period of the optically generated grating was achieved from 584 to 611 nm.

Long lifetime and high repetition rate operation from distributed feedback plastic waveguided dye lasers

Abstract Long lifetime and high repetition rate laser operation was demonstrated from laser-dye-doped waveguides with distributed feedback (DFB) structures. The waveguides were fabricated with a spin-coating and lithography techniques, and DFB structure was written by an ultraviolet holography technique. A compact frequency-doubled Nd:YAG microchip laser was used as a pumping source, and the laser output wavelength range of 575–945 nm was obtained from 10 different kinds of laser-dye-doped plastic film and the laser performance was evaluated about 5 of them. Very low pumping energy requirement of around several μJ could extend the durabilities of the DFB dye-doped waveguides, and the lifetime of more than one million shots was obtained. Further a high repetition laser operation up to 1000 pps was demonstrated with an output energy stability of less than ±0.5%. A palm-top size tunable laser is realized by this configuration.

Positive resist for KrF excimer laser lithography

In order to develop a new positive-tone, chemically amplified photoresist for 248 nm lithography, a copolymer containing acrylic silicon moiety was synthesized. The copolymer of 1,3-bis(trimethylsilyl)isopropyl methacrylate and 4-hydroxystyrene was prepared by free radical polymerization. The polymer structure, properties and acid catalyzed deprotection were evaluated by 1H nuclear magnetic resonance, Fourier transform infrared, UV, thermogravimetric analysis and gel permeation chromatography. This polymer is thermally stable up to 150 °C and is suitably transparent at the KrF laser output wavelength (248 nm). The lithographic evaluation shows the capability of 0.28 μm resolution using a KrF excimer laser stepper.

A high-speed mixed digital-to-analog circuit board for accurate control of wavelength tunable lasers for fiber-optic communications

A mixed digital-to-analog (D/A) high speed circuit board capable of driving a tunable super structure grating distributed Bragg reflector (DBR) laser is developed. The circuit is used to control the laser over a 20-nm tuning wavelength range with 0.1 nm resolution. Three control currents are preprogrammed into an electrically erasable/programmable read-only memory (EEPROM) look-up table for each wavelength. Upon receiving a differential logic control signal, the circuit tunes the laser to the specified output wavelength within 500 ns. The long-term repeatability of the tuned laser output wavelength shows drift below /spl plusmn/0.02 nm with greater than 100 h of operation.

Dye Laser Action by Two-Photon Excitation.

Since dye lasers are very widely tunable from near ultra-violet to near infrared, they have been used in high resolution spectroscopy and many other tunable laser applications. Usually, dye lasers are pumped by onephoton excitation process with shorter wavelength light source compared with laser output wavelength. In this paper, we propose a new excitation method of dye by two-photon process, and also would like to report a numerical calculation of two-photon absorption cross section, as well as a demonstration of laser oscillation by two-photon excitation.

Atomic hyperfine structure studies using temperature/current tuning of diode lasers: An undergraduate experiment

We present a simple and inexpensive experimental arrangement for hyperfine structure studies in atoms using commercially available laser diodes and hollow cathode lamps. The experiment is highly suitable for the undergraduate laboratory. This technique can be employed to investigate the hyperfine structure of rare earth and other elements such as Ta and Nb which have large nuclear magnetic and or quadrupole moments. In this paper, we report well-resolved hyperfine structure spectra recorded for holmium employing optogalvanic spectroscopy. We also report Doppler limited hyperfine structure measurements on the ground state of rubidium using injection current/temperature tuning of the diode laser. This involves a simple experimental arrangement suitable for undergraduate laboratories. The hyperfine coupling constants for the level at 31 443.26 cm−1 in Ho I are reported for the first time. Details of the data analysis to obtain accurate hyperfine structure coupling constants from the observed spectra are presented. A number of commercially available diode lasers in the visible and the near infrared regions and simple in-house developed or commercially available low cost current and temperature controllers can be employed for the present studies. We employ simple cooling/heating or current modulation for tuning the output wavelength of the diode laser. The presently proposed experimental arrangement can be assembled easily and requires no machine/glass shop facilities.

Optical thickness profiling using a semiconductor laser confocal microscope

A semiconductor laser confocal microscope is developed for measuring the optical thickness of thin transparent samples at high spatial resolution. The optical sectioning capability of a confocal microscope, and the sensitivity of the laser output to optical feedback, are both utilized to detect the presence of a nonabsorbing sample in the path of the probe beam that is initially focused onto a plane mirror. The index mismatch at the sample interface defocuses the beam away from the mirror and reduces the amount of optical feedback. The optical thickness is computed from the amount of axial displacement that the mirror must be given to regain maximum feedback. The laser power output is monitored using the monitor photodiode in the laser package. When the geometrical thickness of the sample is known a priori, the technique can be used to measure its refractive index and vice versa. The smallest and largest measurable sample thickness are determined by the sharpness of the axial intensity response of the microscope and the working distance of the focusing objective, respectively. Distortions in the central spot distributions of the response degrade the precision of the measurement technique. We demonstrate the technique for both the 830 and 780 nm laser output wavelengths, by classifying cover glasses of differing optical thickness (geometrical thickness range: 70–536 μm, refractive index=1.523), as well as to image the sudden index changes found in the phase ridge formed by two closely spaced cover glasses (surface flatness=7 μm) of different geometrical thickness. Our experiments show that at least for objectives with small numerical apertures (≤0.25), spherical aberrations are negligible and our measurements are to within the accuracy set by the glass manufacturer.

接合技術 （その１） ５μｍ帯ＣＯレーザーのアルミニウム合金溶接への適用に関する基礎検討

The applicability of a 5-μm-band CO laser to aluminum alloy welding has been investigated. Bead-on-plate welding tests were performed at a power of around 1 kW on various aluminum alloys, and macroscopic observation was made of cross sections of the samples. The penetration depth and threshold power at which the fusion zone shape changes from the heat conduction type to the keyhole type were compared with those obtained using a CO2 laser with similar output beam characteristics. It has been found that for all aluminum alloy samples, the CO laser gives a higher welding capability than the CO2 laser. Because an intense laser-induced plasma is not formed under the experimental conditions, the higher welding capability of the CO laser can be attributed to higher Fresnel absorption due to the shorter output wavelength of the CO laser.

Thermally silver ion exchanged integrated-optic lasers in neodymium-doped silicate glass

Continuous-wave integrated-optic channel waveguide lasers operating near 1.06 μm have been fabricated by thermal silver ion exchange in a commercial neodymium-doped glass. The laser slope efficiency and threshold as a function of waveguide width are measured. The laser output wavelength is also shown to display a dependence on the waveguide width. Optimum laser condition is obtained for waveguide structures with 7.5 μm widths.

Optical detection of ultrasound using a microchip laser

A novel ultrasound detector is presented which uses a microchip laser as the sensing element. An incident acoustic field modulates the optical cavity length of a microchip laser operating in continuous wave mode. The single longitudinal mode laser output wavelength is frequency modulated by the acoustic field. An optical slope filter is used to demodulate the FM signal and generate an intensity modulated optical signal which mimics the acoustic field present in the microchip laser. Parameters are derived for designing the microchip laser for maximum sensitivity and frequency bandwidth. An Nd:YAG microchip laser detecting 5 MHz ultrasound is predicted to have a shot noise limited nonresonantly enhanced sensitivity of 10−4 Pa*(mW/Hz)0.5, a linear dynamic range of 109, and a nearly flat frequency response from dc to slightly below the first acoustic resonance peak. Experimental verification of the sensor operation is presented and compares well with theory. The sensor had a monotonically increasing frequency response from 1 to 7 MHz, with a FM sensitivity of 1–2 MHz/kPa. A large sensitivity enhancement was observed at an acoustic resonance of 8 MHz.

Velocity Selection of Laser Ablated Metal Atoms by a Novel Non-Mechanical Technique

AbstractWe present the results of experiments on velocity selection of fast laser ablated al, Ga, and in atoms by a novel, non-mechanical, technique. Pulses of atoms with broad velocity distributions are produced by laser ablation of a single component pure metal target in vacuum. after a delay of ~ 1 μs, there exists a strong one-to-one correlation between atomic velocity and distance traveled from the ablated surface. Thus, a second pulsed laser, delayed by ~ 1 μs and crossed at a right angle to the atomic beam, can be used to photoionize only those atoms with unwanted velocities, i.e.: atoms moving too fast or too slow to be hidden behind an opaque mask placed ~ 1 cm from the ablated surface. the photoions, and any ions surviving from the ablation event, are subsequently deflected from the beam by a static magnetic field. by a fortunate coincidence, al, Ga, and in atoms all have very large single photon photoionization cross sections at 193 nm, the output wavelength of the arF excimer laser; thus, well over 95% of the unwanted atoms can be easily photoionized and rejected. We have demonstrated velocity selected al, Ga, and in atom fluxes equivalent to Ф ~ 1011 atoms/(cm2-eV-pulse) at a working distance of 10 cm.

Size effects on the temperature rise in vertical-cavity surface-emitting laser diodes

Thin film size effects cause strong anisotropy and reduction in electrical and thermophysical material properties. This paper studies these effects and the effect of the active region radius on the temperature rise in vertical-cavity surface-emitting laser diodes (SELDs). The temperature rise in the active region of an external-cavity SELD is determined experimentally by measuring the laser output wavelength as a function of the injection current and substrate temperature. Simulation results based on models for the current flow and heat generation agree well with experimental data and they demonstrate that the thin film size effects have a strong influence on the laser temperature rise. The effect of the active region radius is clearly demonstrated by the existence of an optimal value for minimal device temperature rise.

A transfer matrix method based large-signal dynamic model for multielectrode DFB lasers

A large-signal dynamic model capable of modeling the transient behavior of the output power and wavelength of multielectrode DFB lasers is described here. The key feature of the model is the use of a modified form of the transfer matrix method resulting in a time-dependent implementation of this technique. Other features are the inclusion of longitudinal spatial hole burning and nonlinear gain in the model. The versatility of the model is demonstrated in an analysis of the response of a two-electrode DFB laser under large-signal direct current modulation which illustrates the important role played by longitudinal spatial hole burning. The limited use of wavelength tunability in controlling chirp is also demonstrated. However, a scheme to improve the damping mechanism through nonuniform excitation called backbiasing is proposed. Finally, wavelength switching is demonstrated using the model. >