Alphan Sennaroglu

Efficient continuous-wave chromium-doped YAG laser

Continuous-wave power performance of a chromium-doped YAG laser pumped by a Nd:YAG laser is investigated as a function of crystal temperature, output coupling transmission, and emission wavelength. Using a 2%-transmitting output coupler, we obtained as much as 1.9 W of cw output power at 1.45 μm with an absorbed power slope efficiency of 42% when the gain medium was cooled at 3°C. Using the laser efficiency data, we estimated the emission and excited-state absorption cross sections at 1.45 μm and compared them with the previously reported values.

Graphene mode-locked femtosecond Cr:ZnSe laser at 2500 nm

We report, for the first time to our knowledge, femtosecond pulse generation from a graphene mode-locked Cr:ZnSe laser at 2500 nm. To minimize the insertion losses at the lasing wavelength, high-quality monolayer graphene transferred on a CaF(2) substrate was used in the experiments. Once mode-locking was initiated, the laser generated a stable train of 226 fs pulses with a time-bandwidth product of 0.39. The mode-locked laser operated at a pulse repetition rate of 77 MHz and produced 80 mW output power with an incident pump power of 1.6 W. To our knowledge, this is the longest laser wavelength at which graphene-based passive mode-locking has been demonstrated to date.

Development of highly luminescent and cytocompatible near-IR-emitting aqueous Ag2S quantum dots

Colloidally stable and highly luminescent near-IR emitting Ag2S quantum dots (NIRQDs) were prepared by a very simple aqueous method using 2-mercaptopropionic acid (2MPA) as a coating. Emission of Ag2S-2MPA NIRQDs can be tuned between 780 and 950 nm. These NIRQDs have photoluminescence quantum yields (PLQY) around 7–39% and exhibit excellent cytocompatibility even at 600 μg mL−1 in NIH/3T3 cells. With such improved properties, Ag2S-2MPA NIRQDs have a great potential in practical bio-applications.

Continuous-wave self-mode-locked operation of a femtosecond Cr 4+ :YAG laser

Continuous-wave self-mode-locked operation of a chromium-doped YAG laser pumped by a continuous-wave Nd:YAG laser at 20 degrees C is described. We used both regenerative initiation and continuous-wave self-mode-locking techniques to generate nearly transform-limited pulses of 120-fs (FWHM) duration at 1.52 microm. The TEM(00) output power was as high as 360 mW. The output of this femtosecond source was tunable from 1.51 to 1.53 microm.

Kerr-lens mode-locked femtosecond Cr(2+):ZnSe laser at 2420 nm.

We describe a cw Kerr-lens mode-locked Cr(2+):ZnSe laser pumped by a 1800 nm thulium fiber laser. The astigmatically compensated asymmetric x cavity contained a 2.4-mm-long Cr(2+):ZnSe sample with a pump absorption coefficient of 11.6 cm(-1) and was operated with a 1% output coupler. The dispersion compensation was achieved by using a MgF(2) prism pair. During Kerr-lens mode-locked operation, we could generate 95 fs pulses at a pulse repetition rate of 94.3 MHz and with 40 mW of output power. The center wavelength of the pulses was 2420 nm. The pulses had a spectral width of 69 nm and a time-bandwidth product of 0.335, which is close to the transform limit for hyperbolic secant pulses.

Intracavity-pumped Cr2+:ZnSe laser with ultrabroad tuning range between 1880 and 3100 nm

We obtained, what is to our knowledge, record tuning from an intracavity-pumped gain-switched Cr2+:ZnSe laser. In the experiments, a polycrystalline Cr2+:ZnSe sample with an absorption of about 43% at 1570 nm was used to minimize reabsorption losses at the lasing wavelengths below 2000 nm. By placing the gain medium inside the cavity of a pulsed KTP optical parametric oscillator (OPO) operating at 1570 nm, smooth, continuous tuning was achieved in the 1880-3100 nm range with four different sets of cavity optics. As high as 145 mW of average laser output power was obtained at 2365 nm with 1.2 W of intracavity OPO power.

Mode-locked Cr 2+ :ZnSe laser

We describe active mode locking of a Cr(2+):ZnSe laser operating near 2.5 mum. The laser produces 4.4-ps transform-limited Gaussian-shaped pulses and produces 82 mW of average power.

Generation of tunable femtosecond pulses in the 1.21-1.27 /spl mu/m and 605-635 nm wavelength region by using a regeneratively initiated self-mode-locked Cr:forsterite laser

A detailed description of the design and operational characteristics of a regeneratively initiated, self-mode-locked Cr:forsterite laser pumped by a continuous-wave Nd:YAG laser is given. Without compensating for the intracavity positive group velocity dispersion, regenerative acoustooptic modulation produced pulses of between 41 and 6.5 ps (FWHM) at 1.23 /spl mu/m with average output powers of between 280 and 380 mW, respectively. Using intracavity negative group-velocity-dispersion compensation, nearly transform-limited femtosecond pulses of 48 fs (FWHM) duration were generated with average TEM/sub 00/ output powers of 380 mW at 1.23 /spl mu/m. By tuning the output of the mode-locked laser from 1.211 to 1.264 /spl mu/m, the dispersion (second and third order) of the Cr:forsterite gain medium has been measured. The operational wavelength range of the laser was extended to the visible region from 605 to 635 nm by external frequency doubling in a LiIO/sub 3/ nonlinear crystal. With approximately 250 mW of fundamental pump power at 1.23 /spl mu/m, red pulses of 116 fs (FWHM) duration at 615 nm were obtained with conversion efficiencies approaching 10 percent. >

Design criteria for Herriott-type multi-pass cavities for ultrashort pulse lasers

We investigate the general characteristics of Herriott-type multipass cavities (MPC) for femtosecond lasers. MPCs can be used to increase the laser pulse energy by extending the laser cavity path length and decreasing the repetition rate, as well as to make standard repetition rate lasers more compact. We present an analytical design condition for MPCs which preserve the Gaussian beam q parameter, enabling the laser path length to be extended while leaving the Kerr-lens modelocking operating point of the cavity invariant. As a specific example, we analyze q preserving MPCs consisting of a flat and curved mirror to obtain analytical expressions for the cavity length. This predicts the optimum MPC designs that minimize the pulse repetition rate for given specifications. These design conditions should prove useful for designing a wide range of high pulse energy or compact femtosecond lasers.

Low-cost, single-mode diode-pumped Cr:Colquiriite lasers

We present three Cr3+:Colquiriite lasers as low-cost alternatives to Ti:Sapphire laser technology. Single-mode laser diodes, which cost only