H.S. Vora

Design of a transversely pumped, high repetition rate, narrow bandwidth dye laser with high wavelength stability

The paper presents the design and performance of a transversely pumped, narrow bandwidth, high wavelength stability tunable dye laser that neither uses low expansion coefficient materials for construction nor incorporates any active control on the wavelength or the dye solution and environmental temperature as generally used in such lasers. The scheme essentially involves designing the mechanical assembly in such a way that, when bolted together it forms a massive monoblock, enclosing all the optical components and the dye laser axis within itself. This ensures the environmental temperature changes can only affect the output characteristics over long time scale. Short term (pulse to pulse) fluctuations in wavelengths and bandwidths, generally associated with the dye flow instabilities, were minimized by using a specially designed a dye cell made of a near 360°-curved rectangular duct, in which the turbulent flow is transformed itself into laminar flow as it reaches the dye laser axis. The laser was operat...

Study on the quality of interference fringes from a pulsed UV source for application in a biprism based fiber Bragg grating writing

This paper presents a study on the quality of interference fringes formed from a pulsed UV (255 nm, 5.6 kHz, and 40 ns) source for an application in writing fiber Bragg gratings (FBGs). The interference fringes of separation of about 8 microm, formed by a biprism of apex angle 2 degrees , were studied for their contrast, evolution of contrast, and positional and intensity stability over a period of 5 min (over 10(6) pulses). Second harmonic UV (255 nm) sources of different spatial coherence and pointing stability characteristics were employed as the inputs. It is established that the UV fringes contrast and interference pattern stability with time is largely controlled by the optical resonator geometry of the fundamental wavelength (510 nm) copper vapor laser (CVL) oscillator. In particular, the generalized diffraction filtered resonator (GDFR) CVL produced the highest quality second harmonic beam with the highest fringes contrast and stability. The implications of these results were studied by employing these UV sources for the fabrication of the C-band FBGs by a 24 degrees apex angle biprism.

Cylindrical-lens-based wavefront-reversing shear interferometer for the spatial coherence measurement of UV radiations

We present the design and results of a cylindrical-lens-based reversal shear interferometer for measuring the spatial coherence of partially or fully coherent UV beams. This is a modified Michelson interferometer consisting of only four optical components. The wavefront is reversed in one of the interferometers arm by the combination of a plane mirror located at the focal plane of a cylindrical lens. The selected wavefront can be sheared at any arbitrary angle with respect to the incident wavefront by rotating the cylindrical lens, thus enhancing the capability of this design for a real 3-D wavefront evaluation. This interferometer is used to measure the spatial coherence of 255-nm UV radiations obtained from the second harmonic of a copper vapor laser for pump beams of different spatial coherence characteristics, a result being reported for the first time.

Studies on characteristics of CO2 laser-GTAW hybrid welding of austenitic stainless steel

The present paper describes an experimental hybrid welding study, involving CO2 laser and gas tungsten arc welding, on 6 mm thick austenitic stainless steel sheet. The study focused on real-time plasma monitoring during welding and metallographic examination of the resultant weldments. Coupling of laser-generated plasma and gas tungsten arc was achieved by introducing argon cross jet. The results of the study demonstrated that for obtaining deep hybrid welds, incident laser power density should be above a threshold to generate metal plasma on its own. An increase in arc current with laser power density below the threshold value resulted in broader conduction-limited welds without causing much change in the weld depth. Coupling of arc with laser also served to stabilize and enhance metal plasma formation, which, in turn, facilitated stabilization of the resultant welding process. Best hybrid welds were achieved when arc followed laser beam along the direction of welding.

Design, modeling, and performance evaluation of a novel dye cell for a high repetition rate dye laser

In this paper, a new dye cell for transverse pumping was designed, modeled, and its performance in a narrow spectral width dispersive resonator, pumped by a high repetition rate copper vapor laser, was investigated. The scheme essentially involves the profiling of the cubical glass and stainless steel cylindrical surface such that convex-plano contour be present near the optical pumping region. The design is an amalgamation of straight and curved periphery to enhance the dye solution flow stabilities near the dye laser axis. A computational fluid dynamics analysis of the liquid flow through this dye cell has been carried out. The dye laser outputs such as optical average power, spectral width and wavelength stability, tuning range, pulse shape, through this new dye cell was evaluated. The dye laser average power about 30 mW was fairly steady over the observation period of more than an hour. The dye laser short-term (1 min) spectral width was within 0.824 ± 0.075 GHz, while, in a long-term, more than an hour, drifted by about 180 MHz. The dye laser wavelength in short-term fluctuates within ±0.0065 nm whereas in a long-term, more than an hour, drifted by about 0.0105 nm. The dye laser tuning range was 10 nm with a sub GHz spectral width operation. The pulse shape of the dye laser follows the pump laser pulse profile. Thus, the dye laser has demonstrated fairly long-term stability, without the use of either low expansion material or close loop control on the output.

Influence of buffer gas pressure on the spectral width of the 510.6-nm line of an atomic copper vapor laser

Abstract. The effect of buffer gas pressure on the intensity and thespectral width of the 510.6-nm line of an atomic copper vapor laser CVL is reported. A self-discharge heated CVL tube of internal diameter47 mm and length 1500 mm was used. The buffer gas pressure wasvaried from 5.0 to 470.0 mbar. A Fabry–Perot etalon-based setup wasused to measure and analyze the spectral width of 510.6-nm lines ofCVL. The relative intensity and spectral width of the hyperfine compo-nents changes with operating buffer gas pressure. The buffer gas pres-sure reduces the number of hyperfine components and hence overalllinewidth .

A study of flow characteristics of a high repetition rate dye laser gain medium

The gain medium of a high repetition rate liquid dye laser is made to flow at a sufficiently high velocity through the dye cell in order to minimize the thermal inhomogeneity. In this paper, temperature contours as a function of distance from the pump beam entrance dye cell window wall at various flow velocities in the laminar and turbulent region of gain medium flow were evaluated using computational fluid dynamics (CFD). Appreciable temperature gradients subsist at low Reynolds numbers due to inefficient heat transfer from the gain medium. However, at high Reynolds numbers >6000, the substantial effects of local density turbulent fluctuations degrade the optical quality of the gain medium. These computational studies were used to elucidate the characteristics of observed spectral fluctuations of a dye laser as a function of the Reynolds number.

Spectral fluctuations of a high repetition rate dye laser through a flowing gain medium

In this paper, wavelength and bandwidth fluctuations of a Rhodamine 6G dye laser, transversely pumped by CVL, through a flowing gain medium are investigated. The gain medium mass flow rates were varied in the range 1?6?l?min?1 (LPM). Analysis of the wavelength and bandwidth fluctuations of the dye laser was carried out using a high resolution Fabry?Perot etalon based setup and composite images generated from spectral profiles. The wavelength varied within 0.0290, 0.0240, 0.0200, 0.0120, 0.0110 and 0.0200?nm while the bandwidth was within 1.340, 0.912, 0.679, 0.301, 0.296 and 0.509?GHz at flow rates of 1.0, 2.0, 3.0, 4.0, 5.0 and 6.0?LPM, respectively. The minimum fluctuations, which depend on the experimental conditions, were observed at ?5?LPM. Spectral fluctuations at particular flow rates depend mainly on the microscopic fluctuations in the temperature and flow velocity inside the boundary layers.