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Chakravarty U, Kuruvilla A, Singh R, Upadhyaya BN, Bindra KS, Oak SM. Generation of more than 40 W of average output power from a passively Q-switched Yb-doped fiber laser. Appl Opt 2016; 55:288-296. [PMID: 26835764 DOI: 10.1364/ao.55.000288] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
We report on the generation of 41.6 W of average output power from a passively Q-switched ytterbium-doped fiber laser using Cr4+:YAG crystal as a saturable absorber (SA). This is the highest average power from passively Q-switched fiber lasers reported so far in the literature, to our knowledge, and it has been achieved by using a specially designed T-type double-end pumping configuration. Variation in average output power, pulse energy, pulse duration, pulse frequency, and pulse-to-pulse stability has also been studied using SAs of different linear transmissions. The effect of an intracavity SA on self-pulsing dynamics was also investigated and it was observed that, at lower input pump power near threshold, the presence of an SA enhances the peak power of relaxation oscillations to trigger the generation of stimulated Raman scattering in the gain fiber. With an increase in pump power, when the passive Q-switching threshold is reached, high peak power random self-pulses regenerate into low amplitude regular Q-switched pulses. The effect of the length of the gain medium on dual-wavelength generation at very low input pump power and broadband generation at sufficiently higher pump power has also been explored.
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Kumar R, Dixit VK, Sinha AK, Ganguli T, Mukherjee C, Oak SM, Sharma TK. Study of the microstructure information of GaAs epilayers grown on silicon substrate using synchrotron radiation. J Synchrotron Radiat 2016; 23:238-243. [PMID: 26698069 DOI: 10.1107/s1600577515019955] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/02/2015] [Accepted: 10/21/2015] [Indexed: 06/05/2023]
Abstract
Williamson-Hall (WH) analysis is a well established method for studying the microstructural properties of epilayers grown on foreign substrates. However, the method becomes inapplicable in specific cases where the structure factor considerations and the presence of anti-phase domains forbid the data acquisition for certain reflections in conventional high-resolution X-ray diffraction (HRXRD) measurements. Here, this limitation is overcome by exploiting the large intensity (25 µW mm(-2)) and high photon energy (15.5 keV) of the X-ray beam obtained from a synchrotron radiation source. The lateral coherence length, vertical coherence length, tilt and micro-strain of GaAs epilayers grown on Si substrate have been successfully measured using the conventional WH analysis. The microstructure information obtained from the conventional WH analysis based on the data acquired at the synchrotron radiation source is in reasonable agreement with the results obtained from atomic force microscope and surface profiler measurements. Such information cannot be obtained on a laboratory-based HRXRD system where modification of the WH method by involving a set of parallel asymmetric crystallographic planes is found to be essential. However, the information obtained from the modified WH method is along a different crystallographic orientation.
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Affiliation(s)
- Ravi Kumar
- Semiconductor Physics and Devices Laboratory, Raja Ramanna Centre for Advanced Technology, Indore 452 013, India
| | - V K Dixit
- Semiconductor Physics and Devices Laboratory, Raja Ramanna Centre for Advanced Technology, Indore 452 013, India
| | - A K Sinha
- Indus Synchrotron Utilization Division, Raja Ramanna Centre for Advanced Technology, Indore 452 013, India
| | - Tapas Ganguli
- Indus Synchrotron Utilization Division, Raja Ramanna Centre for Advanced Technology, Indore 452 013, India
| | - C Mukherjee
- Mechanical and Optical Support Section, Raja Ramanna Centre for Advanced Technology, Indore 452 013, India
| | - S M Oak
- Semiconductor Physics and Devices Laboratory, Raja Ramanna Centre for Advanced Technology, Indore 452 013, India
| | - T K Sharma
- Semiconductor Physics and Devices Laboratory, Raja Ramanna Centre for Advanced Technology, Indore 452 013, India
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Sundar R, Hedaoo P, Ranganathan K, Soni JK, Bindra KS, Oak SM. Modular pump geometry for diode side-pumped high-power Nd:YAG rod laser. Appl Opt 2015; 54:9855-9862. [PMID: 26836549 DOI: 10.1364/ao.54.009855] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
In this paper, we present a modular design configuration to side-pump an Nd:YAG rod of a diode-pumped high-power CW laser. Independent modules in the form of discs are loaded with three-diode linear bar arrays at 120° with respect to each other and are assembled along the length of the rod. By keeping successive discs at three different angular separations (the minimum, intermediate, and maximum), helical, 60° rotated, and linear geometries, respectively, were created. Parameters like thermal lensing, fluorescence profile, laser beam profile, and beam quality factor (M2) were studied to compare the performances of different geometries. The results indicate that the 60° rotated configuration provides the best performance when compared with rest of the schemes. To the best of our knowledge, this is the first time that such novel modular-type pump geometries with a provision for the angular separation of pump diodes have been tried.
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George J, Thakur P, Bindra KS, Oak SM. Demonstration of CW mode locked Cr:forsterite laser using self-shortening and transverse mode degeneracy driven mode locking. Appl Opt 2014; 53:7749-7752. [PMID: 25403000 DOI: 10.1364/ao.53.007749] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
This paper reports a nearly Fourier transform limited CW mode locked Cr:forsterite laser at 1282 nm, with 131 fs pulse duration, based on self-shortening and transverse mode degeneracy (TMD) driven mode locking, operating near the point of fourth-order TMD. The cavity employs a combination of instantaneous intensity driven self-shortening, and operation on the right side of the fourth-order TMD, to generate the self-amplitude modulation necessary for self-mode locking.
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Jana D, Porwal S, Sharma TK, Kumar S, Oak SM. Pump-probe surface photovoltage spectroscopy measurements on semiconductor epitaxial layers. Rev Sci Instrum 2014; 85:043909. [PMID: 24784628 DOI: 10.1063/1.4871990] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
Pump-probe Surface Photovoltage Spectroscopy (SPS) measurements are performed on semiconductor epitaxial layers. Here, an additional sub-bandgap cw pump laser beam is used in a conventional chopped light geometry SPS setup under the pump-probe configuration. The main role of pump laser beam is to saturate the sub-bandgap localized states whose contribution otherwise swamp the information related to the bandgap of material. It also affects the magnitude of Dember voltage in case of semi-insulating (SI) semiconductor substrates. Pump-probe SPS technique enables an accurate determination of the bandgap of semiconductor epitaxial layers even under the strong influence of localized sub-bandgap states. The pump beam is found to be very effective in suppressing the effect of surface/interface and bulk trap states. The overall magnitude of SPV signal is decided by the dependence of charge separation mechanisms on the intensity of the pump beam. On the contrary, an above bandgap cw pump laser can be used to distinguish the signatures of sub-bandgap states by suppressing the band edge related feature. Usefulness of the pump-probe SPS technique is established by unambiguously determining the bandgap of p-GaAs epitaxial layers grown on SI-GaAs substrates, SI-InP wafers, and p-GaN epilayers grown on Sapphire substrates.
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Affiliation(s)
- Dipankar Jana
- Semiconductor Physics and Devices Lab., Raja Ramanna Centre for Advanced Technology, Indore-452013, M. P., India
| | - S Porwal
- Semiconductor Physics and Devices Lab., Raja Ramanna Centre for Advanced Technology, Indore-452013, M. P., India
| | - T K Sharma
- Semiconductor Physics and Devices Lab., Raja Ramanna Centre for Advanced Technology, Indore-452013, M. P., India
| | - Shailendra Kumar
- Indus Synchrotrons Utilization Division, Raja Ramanna Centre for Advanced Technology, Indore-452013, M. P., India
| | - S M Oak
- Semiconductor Physics and Devices Lab., Raja Ramanna Centre for Advanced Technology, Indore-452013, M. P., India
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Choubey A, Singh A, Modi MH, Upadhyaya BN, Lodha GS, Oak SM. Study on effective cleaning of gold layer from fused silica mirrors using nanosecond-pulsed Nd:YAG laser. Appl Opt 2013; 52:7540-7548. [PMID: 24216656 DOI: 10.1364/ao.52.007540] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/16/2013] [Accepted: 09/25/2013] [Indexed: 06/02/2023]
Abstract
A study on effective laser cleaning of gold layer deposited on fused silica substrates used in beamlines of synchrotron radiation (SR) sources using nanosecond-pulsed Nd:YAG laser has been carried out. The influence of pulse duration, beam incidence angle, spot overlapping, laser fluence, and number of passes on cleaning efficiency has been investigated. An approximately 48 nm thick gold layer from a mirror surface area of ~48 cm2 has been cleaned in 3 min. Laser clean quality and efficiency has been analyzed using microscope, scanning electron microscope (SEM), and angle-dependent reflectivity measurement techniques using SR beamline. Optimization of cleaning parameters resulted in a cleaning efficiency of ~98%. This study provides an alternate and low-cost solution for reuse of gold-coated, damaged mirrors.
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Choubey A, Vishwakarma SC, Misra P, Jain RK, Agrawal DK, Arya R, Upadhyaya BN, Oak SM. A highly efficient and compact long pulse Nd:YAG rod laser with 540 J of pulse energy for welding application. Rev Sci Instrum 2013; 84:073108. [PMID: 23902045 DOI: 10.1063/1.4812635] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
We have developed an efficient and high average power flash lamp pumped long pulse Nd:YAG laser capable of generating 1 kW of average output power with maximum 540 J of single pulse energy and 20 kW of peak power. The laser pulse duration can be varied from 1 to 40 ms and repetition rate from 1 to 100 Hz. A compact and robust laser pump chamber and resonator was designed to achieve this high average and peak power. It was found that this laser system provides highest single pulse energy as compared to other long pulsed Nd:YAG laser systems of similar rating. A slope efficiency of 5.4% has been achieved, which is on higher side for typical lamp pumped solid-state lasers. This system will be highly useful in laser welding of materials such as aluminium and titanium. We have achieved 4 mm deep penetration welding of these metals under optimized conditions of output power, pulse energy, and pulse duration. The laser resonator was optimized to provide stable operation from single shot to 100 Hz of repetition rate. The beam quality factor was measured to be M(2) ~ 91 and pulse-to-pulse stability of ±3% for the multimode operation. The laser beam was efficiently coupled through an optical fiber of 600 μm core diameter and 0.22 numerical aperture with power transmission of 90%.
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Affiliation(s)
- Ambar Choubey
- Solid State Laser Division, Raja Ramanna Centre for Advanced Technology, Indore, Madhya Pradesh 452013, India.
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George J, Seihgal R, Oak SM, Mehendale SC. Beam quality degradation of a higher order transverse mode beam due to spherical aberration of a lens. Appl Opt 2009; 48:6202-6206. [PMID: 19904317 DOI: 10.1364/ao.48.006202] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
An analysis of the increase in the beam-propagation factor, M2, of a higher order transverse mode beam caused by quartic phase aberration after transmission through a spherically aberrated lens is reported. The analysis shows that for a given beam size, the increase in the M2 parameter is less for a higher order transverse mode beam as compared to that for a diffraction limited beam. Experimental results using a multimode laser diode beam show good agreement with the theoretical results.
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Affiliation(s)
- Jogy George
- Raja Ramanna Centre for Advanced Technology, Indore, India 452 013.
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Krishnan S, Bindra KS, Oak SM. A sensitive and high dynamic range cw laser power meter. Rev Sci Instrum 2008; 79:125101. [PMID: 19123586 DOI: 10.1063/1.3033165] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
We report the design of a cost effective, highly sensitive cw laser power meter with a large dynamic range based on a photodiode. The power meter consists of a photodiode, a current to voltage converter circuit, an offset balancing circuit, a microcontroller, an analog to digital converter, reed relays, and an alphanumeric liquid crystal display. The power meter can record absolute laser power levels as low as 1 pW. The dynamic range measured with a cw laser at a wavelength of 532 nm is 8x10(10). The high sensitivity and large dynamic range are achieved by the implementation of an analog background balancing circuit and autoranging.
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Affiliation(s)
- S Krishnan
- Laser Physics Applications Division, Raja Ramanna Centre for Advanced Technology, Indore 452013, India.
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Abstract
We present the study of optical limiting in iron oxide nanoparticles of diameters 31, 44, and 61 nm dispersed in toluene under exposure to nanosecond laser pulses at 532 nm. In the low fluence region smaller size nanoparticles show better optical limiting compared to larger size nanoparticles while in the high fluence region all the three samples show same limiting performance. Experimental results were compared with the well reported limiter fullerene C(60) dissolved in toluene. Iron oxide nanoparticles show better optical limiting compared to C(60) in the intermediate fluence region and comparable performance in the high fluence region. The pico-second Z-scan studies indicate that the contribution of electronic nonlinear refractive index and the two-photon absorption to the optical limiting is negligible. Our observations further indicate that the dominant mechanism for the optical limiting in iron oxide nanoparticles is nonlinear scattering.
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Affiliation(s)
- C P Singh
- Laser Physics Application Division, Raja Ramanna Centre for Advanced Technology, Indore-452013 India
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Sundar R, Ranganathan K, Oak SM. Generation of flattened Gaussian beam profiles in a Nd:YAG laser with a Gaussian mirror resonator. Appl Opt 2008; 47:147-152. [PMID: 18188194 DOI: 10.1364/ao.47.000147] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/25/2023]
Abstract
We report the experimental generation of a family of flattened Gaussian beams with bell-shaped, flattened, and annular intensity profiles in an electro-optically Q-switched Nd:YAG laser with a variable reflectivity mirror of a Gaussian reflectivity profile as an output coupler. The laser beams of different profiles were generated by modifying the resonator magnification. The propagation characteristics of the experimentally generated flat Gaussian beams were found to be in agreement with theory. To the best of our knowledge this is the first time such a family of flattened Gaussian beams is experimentally generated intracavity using a single variable reflectivity mirror.
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Affiliation(s)
- R Sundar
- Raja Ramanna Centre for Advanced Technology, Indore, India.
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Upadhyaya BN, Chakravarty U, Kuruvilla A, Thyagarajan K, Shenoy MR, Oak SM. Mechanisms of generation of multi-peak and mode-locked resembling pulses in Q-switched Yb-doped fiber lasers. Opt Express 2007; 15:11576-11588. [PMID: 19547516 DOI: 10.1364/oe.15.011576] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
The output pulse characteristics of Q-switched Yb-doped fiber lasers have been investigated experimentally. It has been observed that for any typical modulation frequency, the pump power and the modulator OFF-time govern the shape of the output Q-switched pulse. At a fixed modulation frequency, with a fine adjustment of acousto-optic modulation window ON-time, pump power and cavity mirror position, it was possible to obtain modulation free single-peak pulse, multi-peak pulse, mode-locked resembling pulse and multi-pulse structured pulse shapes in a Q-switched fiber laser output. These observations have been analyzed and explained. Our investigations show that multi-peak pulse output is due to onset of nonlinear phenomena like SBS and SRS. Similarly, we have found that the mode-locked resembling periodically modulated output pulse shape is due to mode beating between the zeroeth order and the first order diffracted beams of the intra-cavity acousto-optic Q-switch.
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Bindra KS, Chari R, Shukla V, Singh A, Ida S, Oak SM. Two-photon absorption and nonlinear refraction in commercial colour glass filters. ACTA ACUST UNITED AC 1999. [DOI: 10.1088/1464-4258/1/1/010] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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Abstract
The uniformity of film development was investigated for eight different film developing methods including both hand and machine processes. Film uniformity was quantitated through microdensitometry by scanning rolls of uniformly fogged and developed film with an Olympus MMSP microspectrophotometer and a Photometrics EDP scanning microscope. The results of this study showed that significant differences of uniformity were produced using the different developing methods evaluated. With the exception of the tray and hand brushing method, all the machine processors studied produced films having significantly better uniformity than any hand methods evaluated.
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