A distributed feedback dual-gate graphene-channel field-effect transistor (DFB-DG-GFET) was fabri... more A distributed feedback dual-gate graphene-channel field-effect transistor (DFB-DG-GFET) was fabricated as a current-injection terahertz (THz) light-emitting laser transistor. We observed a broadband emission in a 1–7.6-THz range with a maximum radiation power of ~10 μW as well as a single-mode emission at 5.2 THz with a radiation power of ~0.1 μW both at 100 K when the carrier injection stays between the lower cutoff and upper cutoff threshold levels. The device also exhibited peculiar nonlinear threshold-like behavior with respect to the current-injection level. The LED-like broadband emission is interpreted as an amplified spontaneous THz emission being transcended to a single-mode lasing. Design constraints on waveguide structures for better THz photon field confinement with higher gain overlapping as well as DFB cavity structures with higher Q factors are also addressed towards intense, single-mode continuous wave THz lasing at room temperature.
2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC)
The ultrafast optical radiation in the yellow spectral region is of great interest for variety of... more The ultrafast optical radiation in the yellow spectral region is of great interest for variety of scientific and technological applications including astronomy, spectroscopy and medicine, with potential to revolutionize eye surgeries through exquisite accuracy [1, 2]. However, it is relatively difficult to access the yellow region, especially when good beam quality, high power and high efficiency are required. Till date, various types of yellow lasers have been reported [3, 4] mostly in CW regime and nanosecond timescales. Here, we report on a compact, high-power, high repetition-rate, ultrafast source of yellow radiation. Using an ultrafast Cr2+:ZnS laser of average power of 4.5 W with spectral width of Δλ=138 nm centered at 2.36 μm, producing output pulses of width ∼40 fs at a repetition rate of 80 MHz, and two stage single-pass second harmonic generation (SHG), we have generated ultrafast radiation of power 1 W tunable across 577–589 nm. The schematic of the experimental setup is shown in Fig. 1(a). The single-pass SHG of Cr2+:ZnS laser in a 2 mm long 5% mol doped MgO:PPLN multi-grating crystal (Λ=33.15–35.25 μm), giving second harmonic (SH) pulses of 90 fs at 1.18 μm, with a maximum average power of 2.3 W at a single-pass efficiency as high as 65%. Further the 1.18 μm radiation is frequency-doubled in a 1 mm long and 0.5∗1 mm2 in aperture, MgO:PPLN crystal (Λ=8.9 −9.45 μm) producing yellow radiation. The acceptance bandwidth (FWHM) and temporal walk-off length (Lt) of the second crystal are calculated to be 3 nm and 288 μm, respectively. In order to optimize the focusing condition for maximum fourth harmonic generation (FHG) efficiency, we pumped the crystal at constant power of 1.3 W at 1.18 μm and recorded the fourth harmonic (FH) power as a function of focusing parameter, ξ =L/b, where, L is the length of the crystal and b=2πnw02/λ, w0 is the beam waist radius, n is the refractive index of the crystal and λ is the input wavelength.
We report on efficient, two stage single-pass second harmonic generation of ultrafast Cr2+:ZnS la... more We report on efficient, two stage single-pass second harmonic generation of ultrafast Cr2+:ZnS laser with spectral bandwidth of 138 nm centered at ~2360 nm and pulse width of ~43 fs at a repetition rate of 80 MHz into tunable yellow radiation across 577 - 589 nm in multi-grating MgO:PPLN crystals. A maximum average output power ~940 mW at 589 nm wavelength with a single-pass conversion efficiency as high as 41% was achieved. The yellow radiation has a spectral bandwidth of 2 nm and pulse-width of ~913 fs in absence of any pulse compression with a time-bandwidth product of 1.58.
Previous studies have shown that optical and/or injection pumping of graphene can enable negative... more Previous studies have shown that optical and/or injection pumping of graphene can enable negative-dynamic conductivity in the terahertz (THz) spectral range, which may lead to new types of THz lasers and light-emitting devices [1-4]. Recently we obtained preliminary results of single-mode THz lasing in a forward-biased graphene structure with a lateral p-i-n junction in a distributed-feedback dual-gate graphene-channel field-effect transistor (DFB-DG-GFET) [5]. In this work, we experimentally observe amplified spontaneous broadband THz emission from 1 to 7.6 THz at 100K by carrier-injection in a population-inverted DFB-DG-GFET, demonstrating the birth of a new type of THz light-emitting diodes.
We report on amplified spontaneous broadband terahertz emission in 1–7.6 THz range at 100 K via c... more We report on amplified spontaneous broadband terahertz emission in 1–7.6 THz range at 100 K via current injection in a distributed-feedback (DFB) dual-gate graphene-channel transistor. The device exhibited a nonlinear threshold-like behavior with respect to the current-injection level. A precise DFB cavity design is expected to transcend the observed spontaneous broadband emission to single-mode THz lasing.
We report on a compact and simple ultrafast source producing tunable radiation in the near-IR wav... more We report on a compact and simple ultrafast source producing tunable radiation in the near-IR wavelength range. Based on single-pass frequency doubling of an ultrafast Cr2+:ZnS laser at 2360 nm with pulse width of 43 fs at a repetition rate of 80 MHz in MgO:PPLN crystal, the source produces maximum average output power of ∼2.43 W tunable across 1137-1200 nm with a maximum single-pass conversion efficiency as high as 65%. Without use of any pulse compression technique, the source produces output pulses in Gaussian shape with measured pulse width of ∼60 fs and spectral width of 39 nm centered at 1180 nm corresponding to a time-bandwidth product of 0.5. The output beam has a Gaussian spatial profile with measured M2<1.32 and a peak-to-peak power fluctuation of 3% over 2 h. Using MgO:PPLN crystal of two different lengths, 1 mm and 2 mm, we have observed that the optimum second-harmonic generation efficiency of an ultrafast pulse laser, even in the presence of temporal walk-off, appears in the low pump focusing condition.
This paper reports on room-temperature frequency tunable terahertz light amplification by current... more This paper reports on room-temperature frequency tunable terahertz light amplification by current-driven plasmon instabilities produced in a graphene metasurface implemented in an asymmetric dual-grating-gate graphene field effect transistor.
A distributed feedback dual-gate graphene-channel field-effect transistor (DFB-DG-GFET) was fabri... more A distributed feedback dual-gate graphene-channel field-effect transistor (DFB-DG-GFET) was fabricated as a current-injection terahertz (THz) light-emitting laser transistor. We observed a broadband emission in a 1–7.6-THz range with a maximum radiation power of ~10 μW as well as a single-mode emission at 5.2 THz with a radiation power of ~0.1 μW both at 100 K when the carrier injection stays between the lower cutoff and upper cutoff threshold levels. The device also exhibited peculiar nonlinear threshold-like behavior with respect to the current-injection level. The LED-like broadband emission is interpreted as an amplified spontaneous THz emission being transcended to a single-mode lasing. Design constraints on waveguide structures for better THz photon field confinement with higher gain overlapping as well as DFB cavity structures with higher Q factors are also addressed towards intense, single-mode continuous wave THz lasing at room temperature.
2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC)
The ultrafast optical radiation in the yellow spectral region is of great interest for variety of... more The ultrafast optical radiation in the yellow spectral region is of great interest for variety of scientific and technological applications including astronomy, spectroscopy and medicine, with potential to revolutionize eye surgeries through exquisite accuracy [1, 2]. However, it is relatively difficult to access the yellow region, especially when good beam quality, high power and high efficiency are required. Till date, various types of yellow lasers have been reported [3, 4] mostly in CW regime and nanosecond timescales. Here, we report on a compact, high-power, high repetition-rate, ultrafast source of yellow radiation. Using an ultrafast Cr2+:ZnS laser of average power of 4.5 W with spectral width of Δλ=138 nm centered at 2.36 μm, producing output pulses of width ∼40 fs at a repetition rate of 80 MHz, and two stage single-pass second harmonic generation (SHG), we have generated ultrafast radiation of power 1 W tunable across 577–589 nm. The schematic of the experimental setup is shown in Fig. 1(a). The single-pass SHG of Cr2+:ZnS laser in a 2 mm long 5% mol doped MgO:PPLN multi-grating crystal (Λ=33.15–35.25 μm), giving second harmonic (SH) pulses of 90 fs at 1.18 μm, with a maximum average power of 2.3 W at a single-pass efficiency as high as 65%. Further the 1.18 μm radiation is frequency-doubled in a 1 mm long and 0.5∗1 mm2 in aperture, MgO:PPLN crystal (Λ=8.9 −9.45 μm) producing yellow radiation. The acceptance bandwidth (FWHM) and temporal walk-off length (Lt) of the second crystal are calculated to be 3 nm and 288 μm, respectively. In order to optimize the focusing condition for maximum fourth harmonic generation (FHG) efficiency, we pumped the crystal at constant power of 1.3 W at 1.18 μm and recorded the fourth harmonic (FH) power as a function of focusing parameter, ξ =L/b, where, L is the length of the crystal and b=2πnw02/λ, w0 is the beam waist radius, n is the refractive index of the crystal and λ is the input wavelength.
We report on efficient, two stage single-pass second harmonic generation of ultrafast Cr2+:ZnS la... more We report on efficient, two stage single-pass second harmonic generation of ultrafast Cr2+:ZnS laser with spectral bandwidth of 138 nm centered at ~2360 nm and pulse width of ~43 fs at a repetition rate of 80 MHz into tunable yellow radiation across 577 - 589 nm in multi-grating MgO:PPLN crystals. A maximum average output power ~940 mW at 589 nm wavelength with a single-pass conversion efficiency as high as 41% was achieved. The yellow radiation has a spectral bandwidth of 2 nm and pulse-width of ~913 fs in absence of any pulse compression with a time-bandwidth product of 1.58.
Previous studies have shown that optical and/or injection pumping of graphene can enable negative... more Previous studies have shown that optical and/or injection pumping of graphene can enable negative-dynamic conductivity in the terahertz (THz) spectral range, which may lead to new types of THz lasers and light-emitting devices [1-4]. Recently we obtained preliminary results of single-mode THz lasing in a forward-biased graphene structure with a lateral p-i-n junction in a distributed-feedback dual-gate graphene-channel field-effect transistor (DFB-DG-GFET) [5]. In this work, we experimentally observe amplified spontaneous broadband THz emission from 1 to 7.6 THz at 100K by carrier-injection in a population-inverted DFB-DG-GFET, demonstrating the birth of a new type of THz light-emitting diodes.
We report on amplified spontaneous broadband terahertz emission in 1–7.6 THz range at 100 K via c... more We report on amplified spontaneous broadband terahertz emission in 1–7.6 THz range at 100 K via current injection in a distributed-feedback (DFB) dual-gate graphene-channel transistor. The device exhibited a nonlinear threshold-like behavior with respect to the current-injection level. A precise DFB cavity design is expected to transcend the observed spontaneous broadband emission to single-mode THz lasing.
We report on a compact and simple ultrafast source producing tunable radiation in the near-IR wav... more We report on a compact and simple ultrafast source producing tunable radiation in the near-IR wavelength range. Based on single-pass frequency doubling of an ultrafast Cr2+:ZnS laser at 2360 nm with pulse width of 43 fs at a repetition rate of 80 MHz in MgO:PPLN crystal, the source produces maximum average output power of ∼2.43 W tunable across 1137-1200 nm with a maximum single-pass conversion efficiency as high as 65%. Without use of any pulse compression technique, the source produces output pulses in Gaussian shape with measured pulse width of ∼60 fs and spectral width of 39 nm centered at 1180 nm corresponding to a time-bandwidth product of 0.5. The output beam has a Gaussian spatial profile with measured M2<1.32 and a peak-to-peak power fluctuation of 3% over 2 h. Using MgO:PPLN crystal of two different lengths, 1 mm and 2 mm, we have observed that the optimum second-harmonic generation efficiency of an ultrafast pulse laser, even in the presence of temporal walk-off, appears in the low pump focusing condition.
This paper reports on room-temperature frequency tunable terahertz light amplification by current... more This paper reports on room-temperature frequency tunable terahertz light amplification by current-driven plasmon instabilities produced in a graphene metasurface implemented in an asymmetric dual-grating-gate graphene field effect transistor.
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