Journal Articles on Category: Physics and Astronomy

In the present paper, an impact of localization of an oxide aperture within a vertical-cavity surface-emitting diode laser (VCSEL) on its threshold operation is analyzed. As expected, a shift of the aperture from the anti-node position of the standing optical wave within a VCSEL cavity to the node position is followed by a drastic change of the wave guiding mechanism from the index guiding to the gain guiding. Index-guided VCSELs have been found to exhibit much lower threshold currents, but any increase in their active-region diameters over a relatively low critical value is followed by excitation of higher-order modes. On the other hand, the fundamental-mode operation is achieved in gain-guided VCSELs with much larger active regions but at the expense of considerably higher lasing thresholds. Therefore, a new VCSEL design, i.e., the separate confinement oxidation (SCO) VCSEL, is proposed. The SCO VCSELs are expected to combine advantages of both previous oxide-confined VCSELs, i.e., low lasing thresholds of index-guided VCSELs with the fundamental-mode operation of gain-guided ones even in the case of large active regions.

Issn:00785466

Keywords: semiconductor laser ; vertical-cavity surface-emitting diode laser (VCSEL) ; oxide-confined VCSELs ; fundamental-mode operation

Volume: 35

Pages: 635-644

In the high-power semiconductor lasers, the surface of the mirror is the key element of the construction, which has the main impact on the reliability and degradation processes. In the case of lasers fabricated with the use of GaAs compounds the highest power emitted by the structure is limited by the catastrophic optical damage (COD) effect due to the increase of temperature on the air-semiconductor edge. The technique which enables examining the temperature distribution on the mirror surface is thermoreflectance. In this paper, we present the technique of temperature mapping on the mirror surface of the high power semiconductor lasers based on the thermoreflectance method.

Issn:00785466

Keywords: thermoreflectance ; semiconductor laser ; mirrors ; temperature maps

Volume: 35

Pages: 611-617

A technique of time-resolved laser spectra mapping has been developed to assess thermo-optical properties of diode lasers. Using this technique the emission spectra of broad contact pulse operated diode lasers were measured for consecutive time points within the pulse duration width. The emitted wavelength was found to be highly dependent on the time elapsing from the pulse front and a time shift of wavelength was clearly observed in the spectrum of pulse-operated lasers.

Issn:00785466

Keywords: thermal dynamics ; SQW laser ; spectrum

Volume: 35

Pages: 573-578

Spatially resolved micro-Raman measurements have been performed to determine temperature distribution over the facet of high power semiconductor diode lasers. This technique is non-invasive and allows one to study the local temperature on the surface of the mirror of semiconductor diode lasers under normal operating conditions. The micro-Raman measurements can also serve as a calibration of absolute temperature for the other contact-less thermometric methods, e.g., thermoreflectance.

Issn:00785466

Keywords: Raman spectroscopy ; catastrophic optical mirror damage (COMD) ; high-power laser ; thermoreflectance

Volume: 35

Pages: 555-560

A method for obtaining the shape of a surface investigated with a laser scanning curvature measurement is presented. Additional simple analysis of raw experimental data allows one to determine waviness of the sample. The accuracy of the method and comparison of the results obtained with the method and commercial profilometer are also described.

Issn:00785466

Keywords: waviness ; curvature ; profilometer

Volume: 35

Pages: 503-507

In this paper we describe a number of optical techniques suitable for estimation of the semiconductor surface temperature. High spatially resolved thermoreflectance will be shown as a powerful tool to measure temperature distribution at the laser diode front facet. For determination of the absolute value of the front facet temperature we use micro-Raman spectroscopy. Both techniques will be presented as a complementary ways to determine surface temperature distribution on the working laser diode.

Issn:00785466

Keywords: thermoreflectance ; Raman spectroscopy ; semiconductor laser

Volume: 35

Pages: 479-484

Laser mass spectrometry is a new chemical trace analysis method with high selectivity, sensitivity and speed. The mass-resolved resonance-enhanced multiphoton ionization (REMPI) spectra of chloroethylenes–trichloroethylene and tetrachloroethylene are firstly reported in the range 305.0–325.0 nm. The mass-resolved excited spectra and laser power index of fragment ions CCl+ are presented. The experimental results indicate that 310.8 nm is the suitable ionization wavelength for detection of trichloroethylene and 322.5 nm for the detection of tetrachloroethylene in this wavelength range. The detection limits of these two chloroethylenes of concentration range expressed in mg/L are presented.

Issn:00785466

Keywords: laser mass spectrometry ; resonance-enhanced multiphoton ionization ; time of flight mass spectrum ; chloroethylenes

Volume: 35

Pages: 395-402

In the paper, changes of the optical and thermodynamic parameters, such as a refractive index, pressure, and temperature are investigated on an RF pulsed CO2 slab-waveguide laser. Changes of the refractive index, and pressure are measured with a Mach–Zehnder interferometer, and microphone, respectively. A Gladstone–Dale formula is applied to calculate the changes of the temperature. It is shown how an acoustic wave in the laser cavity modifies the pressure of the laser medium in the course of the pulse duration. The results of measurements allow explaining a line hopping effect observed during the laser plasma pulse evolution.

Issn:00785466

Keywords: CO2 laser ; slab-waveguide ; RF excitation ; pulse operation ; acoustic wave ; line hoppings

Volume: 35

Pages: 215-224

The absolute absorption spectrum intensities of carbon dioxide sample have been recorded with a tunable diode laser spectrometer in the spectral range 6350–6364 cm–1, which is suitable for the in situ sensing of carbon dioxide in the lower stratosphere using a commercial telecommunication -type diode laser. It was found that the typical uncertainty of experimental line intensities is about 1% compared with the values listed in the HITRAN database, which are calculated by direct numerical diagonalization (DND).

Issn:00785466

Keywords: wavelength modulation ; diode lasers ; absorption spectroscopy

Volume: 35

Pages: 49-57

The slit scan method was implemented for registration of intensity profiles along the caustics of a laser beam. The inverse Radon transform of spatially normalized intensity profiles enables direct computation of Wigner transform of real laser beam. The Rayleigh range, divergence angle, beam quality factor, global degree of coherence can be determined in such a simple way. A procedure enabling derivation of the shape of aberrated wavefornt and spherical aberration content was elaborated. This method was applied for investigation of the aberrated laser beams generated by cw and pulsed diode pumped lasers.

Issn:00785466

Keywords: laser beams ; laser optics ; beam quality ; Wigner transform ; aberrations

Volume: 35

Pages: 33-41