In this lab our primary focus is to develop high power diode pumped intracavity frequency doubled solid-state green (DPSS Green) lasers for various applications related to DAE and DRDO. Apart from the development of state of the art for various kinds of intracavity frequency converted DPSS laser systems we recently started R&D activities on ultrafast fiber lasers and amplifiers. A summary of the recent activities in the lab are listed below:

1. Multicolor laser system:

Nd³⁺doped gain medium like Nd:YVO4 crystal has several lasing transitions such as at 1064 nm, 1342 nm and at 914 nm. Multicolor laser system is an array of lasers that exploits different lasing transitions in Nd:YVO4 crystal and generates different colors by the process of intracavity frequency doubling and frequency mixing. The red , blue and green beam are generated by intracavity frequency doubling of 1342 nm, 914 nm and 1064 nm. To generate the yellow color the laser is forced to oscillate at 1064 nm and 1342nm in a single linear cavity configuration. Then by intracavity frequency mixing of these two wavelengths in KTP crystal yellow beam at 593.5 nm is generated. The individual colors are useful many applications like the blue beam is useful for underwater communication, the red beam is useful for the treatment of skin diseases, green beam is for the treatment of diabetic retinopathy and all the colors together are attractive for laser display or laser show. Further all the four colors can be combined using a multiport fiber coupler to generate high brightness white light beam which can be used for laser projection application.

Photograph of the multicolor laser system	White light by combining the multicolor laser beams

2.Green laser photocoagulator for the treatment of diabetic retinopathy:

The activities on diode-end-pumped green lasers carried out at the lab are culminated in the development of a “laser photocoagulator”. The green laser photocoagulator is a medical equipment which is used for the treatment of diabetic retinopathy. Green laser beam can reach the eye without much absorption in the intermediate ocular media and get absorbed at the excess blood vessels in the retina of the patients suffering from prolonged diabetes enabling controlled cutting and sealing of these blood vessels. The system developed at SSLD, RRCAT is handed over to ‘Aravindo Eye Care Hospital’, Madurai in August, 2008 and is being successfully used for the treatment of diabetic retinopathy. A photograph of the system and a treated retina with this system are shown below.

Green laser Photocoagulator developed at RRCAT	A portion of treated retina with this system

4.High power single frequency green laser:

Based on dual end-pumping scheme of 0.1 at.% Nd:YVO4 crystal unidirectional ring cavity is designed for continuous-wave single frequency green laser beam generation. A maximum 1.5 W of output power at 532 nm was obtained with an optical conversion efficiency of ~3%. The output beam spectrum was analyzed by using a Febry-Perot interferometer with a finess of 200 and 1.5GHz free spectral range and the output green beam line-width was measured to be ~10MHz without any intracavity etalon. The output green power was stable within ±5% during half an hour operation.

Photograph of single frequency DPSS green laser	Output trace from scanning FP interferometer

4. High average power green laser system with short pulse duration:

For efficient pumping of tunable dye laser system high average power green beam with short pulse duration is required. A novel coupled cavity configuration is demonstrated to reduce the green pulse width in intracavity frequency doubled repetitively Q-switched green laser system for the above mentioned application. In an Nd:YAG/KTP based green laser system more than 50 W of average green power with less than 35 ns green pulse duration is demonstrated by employing this coupled cavity configuration at 5 kHz repetition rate. The output power and green pulses are highly stable with much lower jitter as compared to that from the conventional DPSS green laser. The laser was successfully used for efficient pumping of narrow linewidth tunable dye laser in GIG configuration.

DPSS green laser based on coupled cavity	Use of the laser for pumping of Dye laser

5. High power high brightness DPSS green laser:

In a linear cavity configuration using two diffuse reflector based pump heads ~160 W of average green power by intracavity frequency doubling of AO Q-switched Nd:YAG/LBO based laser is demonstrated. The corresponding optical to optical conversion efficiency was estimated to be ~12.7%. The pulse repetition rate is 21 kHz with the individual pulse duration of 73ns. The M2 parameter of the output green beam is measured to be ~19.

Photograph of the high power green laser setup	Beam profile from the green laser

In another laser setup more than 80 W of CW green beam at 532 nm is obtained by intracavity frequency doubling of diode side pumped Nd:YAG/KTP laser in a Z-shaped resonator at a total pumping power of 756 W corresponding to more than 11% optical to optical conversion efficiency.

6.Femtosecond mode-locked Yb-doped fiber laser and amplifier system

Stable mode-locking operation in Yb-doped fiber oscillator in all-normal dispersion ( ANDisp) configuration is demonstrated for the first time in our lab. The laser oscillator is a unidirectional ring cavity made of all-normal dispersion elements. The gain medium was a 80 cm long single mode Yb-doped fiber pumped in-core by a single mode fiber coupled laser diode at 976 nm. The rest of the laser is comprised of standard single mode fiber (SMF), in-fiber polarization controller ( PC1 and PC2),

ML Yb doped fiber oscillator	The preamplifier stage	The Power amplifier stage

polarizing beam splitter (PBS), in-fiber collimators (COL1 and COL2), an optical isolator (ISO) and a narrow band interference filter (bandwidth 10 nm, peak transmission ~1064 nm). The PBS in combination with the in-fiber polarization controllers act like a fast saturable absorber based on nonlinear polarization evolution (NPE) and the narrow band filter helps in pulse-width management. At a pump power of ~300 mW about 100 mW of average power was obtained at the NPE rejection port corresponding to 2.6 nJ of pulse energy. The pulses from the NPE port was coupled to another Yb doped fiber (SMF) which was pumped in-core by another fiber coupled laser diode. Nearly 20 mW of power from the oscillator was coupled to the amplifier which was amplified to 250 mW at a pump power of ~500 mW. This corresponds to a pulse energy of ~7.5 nJ. For power amplification of the pulses we used double clad Yb-doped fiber with 10 micron core diameter and 125 micron inner clad diameter. The fiber was pumped in counter propagation direction to the signal by a multimode fiber coupled laser diode with the help of a couple of lenses. Around 70 mW of signal was coupled to the core of the fiber which was amplified to 4W of power corresponding to 110 nJ of amplified pulse energy. The compressed pulse duration was measured to be ~160 fs with the help of an autocorrelator.

Journals:

Year-2012

1. “Self Q-switched Nd:YVO4 laser at 914 nm”,
   Pradeep K. Gupta, Amarjeet Singh, Sunil K. Sharma, Pranab K. Mukhopadhyay, Kushvinder S. Bindra, and Shrikant M. Oak,
   Review of Scientific Instruments 83, 046110 (2012).

Year-2011

1. “ A simple technique for reduction of the fall time and enhancement of the peak power of diode-side pumped intracavity frequency doubled repetitively Q-switched green laser pulse”,
   Pranab K. Mukhopadhyay, Sunil K. Sharma,  Amarjeet Singh, Shrikant M. Oak
   Review of Scientific Instruments 82, 046113 (2011)
   
   
2. “82 W Continuous Wave Green Beam Generation by Intracavity Frequency Doubling of Diode-Side-Pumped Nd:YAG Laser”,
   A.J. Singh, P. K. Mukhopadhyay, S. K. Sharma, K. Ranganathan and S. M. Oak 
   IEEE Journal of Quantum Electron. 47 (3), 398-405 (2011)
   
   
3. “ Texturing of titanium  (Ti6A14V) medical implant surfaces with MHz repetition rate femtosecond and picosecond  Yb doped fiber lasers.”
   M. Ergodan, B. Oktem, H. Kalaycioglu, S. Yavas, P. K. Mukhopadhyay, K. Eken, Y. Aykac, U. Tazebay, and F.Ilday,
   Optics Express Vol. 19, pp. 10986-10996 (2011).
   
   
4. “Core–shell nanophosphor with enhanced NIR–visible upconversion as spectrum modifier for enhancement of solar cell efficiency”, 
   A. F. Khan , R. Yadav, P. K. Mukhopadhyay , S. Singh, C. Dwivedi , V. Dutta, S. Chawla,
   Journal of Nanoparticle Research, Vol. 13, pp. 6837-6846, (2011).

Year-2010

1. “A simple, compact, and efficient diode-side-pumped linear intracavity frequency doubled Nd:YAG rod laser with 50 ns pulse width and 124 W green output power”, Sharma Sunil K., Mukhopadhyay P.K., Singh Amarjeet, Ranganathan K., Oak S.M,
   Review of Scientific Instruments 81(7), 073104-1 -7 (2010)
   
   
2. “101 W of average green beam from diode-side-pumped Nd: YAG/LBO-based system in a relay imaged cavity”,
   Sharma S.K., Singh A.J., Mukhopadhyay P.K., Oak S.M.
   Pramana - Journal of Physics 75, 935-940 (2010)
   
   
3. “Efficient and high-power green beam generation by frequency doubling of acousto-optic Q-switched diode-side pumped Nd: YAG rod laser in a coupled cavity”,
   Sharma S.K., Singh A.J., Mukhopadhyay P.K. and Oak,
   S M Pramana - Journal of Physics 75, 941-945 (2010)
   
   
4. “Dual wavelength operation in diode-end-pumped hybrid vanadate laser”,
   Singh A.J., Sharma S.K., Mukhopadhyay P.K., Oak S.M.
   Pramana - Journal of Physics 75, 929-934 (2010)
   
   
5. “Femtosecond pulse generation and amplification in Yb-doped fibre oscillator amplifier system”, 
   Mukhopadhyay P.K.,
   Pramana - Journal of Physics 75, 787-805 (2010)
   
   
6. “Green laser photocoagulator for the treatment of diabetic retinopathy developed at Raja Ramanna Centre for Advanced Technology”,
   Oak S.M.,
   Pramana: Journal of Physics 75, 1273-1279 (2010)

Year-2009

1. 1. “All-fiber low-noise high-power femtosecond Yb-fiber amplifier system seeded by an all-normal dispersion fiber oscillator”,
   P. K. Mukhopadhyay, Kıvanc¸ Ozgoren, I. Levent Budunoglu, and F. Omer Ilday,
   IEEE Journal of Selected Topics in Quantum Electronics, vol.15 issue 1., pp. 145-152, Jan, 2009.

Year-2008

1. “Aggregated nanoplatelets: optical properties and optically induced deaggregation”,
   J Jayabalan, Asha Singh, Rama Chari1, Himanshu Srivastava, P K Mukhopadhyay, A K Srivastava and S M Oak,
   Journal of Physics: Condensed Matter, vol. 20, p. 445222, 2008.

Conference:

Year-2012

1. “Generation of clean femtosecond pulses from all normal dispersion modelocked Yb doped fiber laser and it’s amplification”,
   P. K. Mukhopadhyay, K. S. Bindra and S. M. Oak,
   Presented at Photonics 12: International conference of fiber optics and photonics, paper id:T3C.3.
   
   
2.  “A comparative study of AO Q-switching in end-pumped Nd:YVO4 and Nd:GdVO4 laser at 1342nm.” ,
   P. K. Gupta, A. J. Singh, S. K. Sharma, P. K. Mukhopadhyay, K. S. Bindra and S. M. Oak,
   accepted for presentation in National Laser Symposium to be held at BARC, Feb, 2013.
   
   
3. “Thermal birefringence compensated linear intracavity frequency doubled Nd:YAG rod laser with 73 ns pulse duration and 160W green output power. S K Sharma”,
   A J Singh, P K Gupta, P Hedaoo, P K Mukhopadhyay, K Ranganathan, K S Bindra and S M Oak
   accepted for presentation in National Laser Symposium to be held at BARC, Feb, 2013
   
   
4. “Improvement of beam quality parameter (M2) of high average power intracavity frequency doubled DPSS green laser.”, 
   A J Singh, S K Sharma, P K Gupta, P K Mukhopadhyay, K S Bindra and S M Oak
   accepted for presentation in National Laser Symposium to be held at BARC, Feb, 2013
   
   
5. “Efficinet Yellow beam genetration by intracavity sum frequency mixing in DPSS Nd:YVO4 Laser.”, 
   A J Singh, P K Gupta, S K Sharma, P K Mukhopadhyay, K S Bindra and S M Oak,
   accepted for presentation in National Laser Symposium to be held at BARC, Feb, 2013

Year-2011

1. “Efficient 147 W of Green Beam Generation by Intracavity Frequency-Doubling of Diode Side-Pumped AO Q-Switched Nd:YAG Rod Laser”,
   S. K. Sharma, A. J. Singh, P. K. Gupta, P. K. Mukhopadhyay, K. S. Bindra and S. M. Oak,
   Proceedings of National Laser Symposium-20, Anna University, Chennai (2012).
   
   
2. “Studies on Near Degenerate OPO for the Generation of Tunable Dual Wavelength Sources”,
   Aditi Dighe, A. J. Singh, P. K. Gupta, S. K. Sharma, P. K. Mukhopadhyay, K. S. Bindra and S. M. Oak,
   Proceedings of National Laser Symposium-20, Anna University, Chennai (2012).
   
   
3. “Yellow beam genetration by intracavity sum frequency mixing in DPSS lasers:        studies on  cavity configurations”,
   A. J. Singh, P. K. Gupta, S. K. Sharma, P. K. Mukhopadhyay, K. S. Bindra and S. M. Oak,
   Proceedings of National Laser Symposium-20, Anna University, Chennai (2012).
   
   
4. “Studies on relaxation oscillation for 4F3/2 -4I9/2 transition in Nd:YVO4 laser incorporating saturable reabsorption loss”,
   P. K. Gupta, A. J. Singh, S. K. Sharma, P. K. Mukhopadhyay, K. S. Bindra and S. M. Oak,
   Proceedings of National Laser Symposium-21, Anna University, Chennai (2012).

Year-2010

1. “Effect of doping concentration in quasi-three level Nd:YVO4 laser at 914 nm”,
   A.J. Singh, S.K.Sharma, P. K. Mukhopadhyay and S.M. Oak,
   Proceedings of National Laser Symposium-09, BARC, Mumbai (2010).
   
   
2. “Dual wavelength operation in diode-end-pumped hybrid vanadate laser”,
   A.J. Singh, S.K. Sharma, P. K. Mukhopadhyay and S.M. Oak,
   Proceedings of National Laser Symposium-09, BARC, Mumbai (2010).
   
   
3. “A comparative study of  Nd:YVO4 and Nd:GdVO4 laser operating  at 1342 nm”,
   A.J. Singh, S.K. Sharma, P. K. Mukhopadhyay and S.M. Oak, 
   Proceedings of National Laser Symposium-09, BARC, Mumbai (2010).
   
   
4. “Efficient and high power green beam generation by frequency doubling of AO Q-switched diode-side pumped Nd:YAG rod laser in a coupled cavity”,
   S.K. Sharma, A.J. Singh, P. K. Mukhopadhyay and S.M. Oak,
   Proceedings of National Laser Symposium-09, BARC, Mumbai (2010). 
   
   
5. “101W of average green beam from diode-side-pumped Nd:YAG/LBO based system in a relay imaged cavity”
   S.K.Sharma, A. J.Singh, P. K. Mukhopadhyay and S.M. Oak,
   Proceedings of National Laser Symposium-09, BARC, Mumbai (2010)
   
   
6. “131W of average green beam generation by intracavity frequency doubling of acousto optically Q-switched Nd:YAG/KTP laser”,
   Sharma S. K., Singh A. J., Mukhopadhyay P. K. and Oak S.M.,
   Proceedings of National Laser Symposium-19, RRCAT, Indore (2010).
   
   
7. “75W of continuous-wave green beam generation by intracavity frequency doubling of diode side pumped Nd:YAG laser”,
   Singh A. J., Sharma S.K., Mukhopadhyay P. K. and Oak S.M.,
   Proceedings of National Laser Symposium-19, RRCAT, Indore (2010)
   
   
8. “Efficient Dye Laser pumping using in house built DPSS green laser”,
   Mukhopadhyay  P. K., Sharma S.K., Singh A. J. , Oak S.M., Prakash Om, Mahakud R., S. K. Dixit and,
   Proceedings of National Laser Symposium-19, RRCAT, Indore (2010).
   
   
9. “A compact diode-end-pumped AO-Q switched intracavity frequency doubled green laser for laser-doping in silicon photocell”,
   Singh A. J., Sharma S. K., Mukhopadhyay P. K. and Oak S. M.,
   Proceedings of National Laser Symposium-19, RRCAT, Indore (2010).
   
   
10. “Surface texturing of dental implant surfaces with an ultrafast fiber laser”,
    B. Oktem, H. Kalaycioglu, M. Erdoğan, S. Yavaş, P.K. Mukhopadhyay, U. H. Tazebay, Y. Aykaç, K. Eken, F. Ö. Ilday, , JTuD-Joint CLEO/QELS
    Poster Session I, JTuD15, San Jose, California (2010).

Year-2009

1. “High energy mode-locked pulse generation in actively q-switched Nd:YVO4 laser using nonlinear mirror”,
   A.J. Singh, S.K. Sharma, P. K. Mukhopadhyay and S. M. Oak,
   Proceedings of National Laser Symposium-08, LASTECH, New Delhi (2009)
   
   
2. "Low-noise high-power ultrafast Yb-fiber amplifier system with integrated pump delivery",
   P. K. Mukhopadhyay, H. Kalaycioğlu, K. Özgören, I. Levent Budunoğlu, and F. Ömer Ilday,
   Paper JTuD65 CLEO, Baltimore, MD, (2009).

Year-2007

1. “Efficient and high power green beam generation using water cooled non gray track resistant KTP crystal”
   A J Singh, S K Sharma, P K Mukhopadhyay, K Ranganathan, S M Oak, 
   Proceedings of National Laser Symposium-07, M. S. University, Vadodra (2007).
   
   
2. “Reduction of fall time of intracavity frequency doubled AO Q-switched green laser pulses”,
   S K Sharma, A J Singh, P K Mukhopadhyay, K Ranganathan, S M Oak,
   Proceedings of National Laser Symposium-07, M. S. University, Vadodra (2007).

News Letters:

1. “Ultrashort pulse generation and amplification in Yb-doped fiber laser”,
   P. K. Mukhopadhyay,
   Kiran, Bulletin of the Indian Laser Association, Vol 20(2), 3 (2009).
   
   
2. “Multi-wavelength diode pumped neodymium doped vanadate lasers”,
   P. K. Mukhopadhyay, A.J. Singh, S. K. Sharma and S. M. Oak, ,
   RRCAT News Letter, Vol 22(2), 34, 2009.