Femtosecond pulse generation from a titanium-doped sapphire laser using nonlinear external cavity feedback

A 33.2 W High Beam Quality Chirped-Pulse Amplification-Based Femtosecond Laser for Industrial Processing

A photonic crystal fiber-based chirped pulse amplification delivering 272 fs pulses of 66.4 µJ energy at a repetition rate of 500 kHz is presented, resulting in an average/peak power of 33.2 W/244 MW. A single grating is adopted for the pulse width stretching and compression, which leads to high-compactness and low cost of the system. The output beam is near-diffraction-limited (M² = 1.1 ± 0.05) with a power stability better than 0.5%. The cutting of alumina ceramic substrate and flexible printed circuit are demonstrated by using the laser system. The results indicate that the laser is competent for industrial applications.

Impulsive Raman spectroscopy via precision measurement of frequency shift with low energy excitation

Stimulated Raman scattering (SRS) has recently become useful for chemically selective bioimaging. It is usually measured via modulation transfer from the pump beam to the Stokes beam. Impulsive stimulated Raman spectroscopy, on the other hand, relies on the spectral shift of ultrashort pulses as they propagate in a Raman active sample. This method was considered impractical with low energy pulses since the observed shifts are very small compared to the excitation pulse bandwidth, spanning many terahertz. Here we present a new apparatus, using tools borrowed from the field of precision measurement, for the detection of low-frequency Raman lines via stimulated-Raman-scattering-induced spectral shifts. This method does not require any spectral filtration and is therefore an excellent candidate to resolve low-lying Raman lines (<200  cm^-1), which are commonly masked by the strong Rayleigh scattering peak. Having the advantage of the high repetition rate of the ultrafast oscillator, we reduce the noise level by implementing a lock-in detection scheme with a wavelength shift sensitivity well below 100 fm. This is demonstrated by the measurement of low-frequency Raman lines of various liquid samples.

Femtosecond pulse generation by using an additive-pulse mode-locked chromium-doped forsterite laser operated at 77 K

Using an acousto-optically mode-locked chromium-doped forsterite laser, operated at 77 K and coupled to a nonlinear resonator containing a single-mode fiber, we have produced femtosecond pulses of 150-fs duration at 1.23 microm with useful output powers of approximately 60 mW This represents what is to our knowledge the first demonstration of femtosecond pulse generation from this laser system using the coupled-cavity mode-locking scheme.

Continuously self-mode-locked Ti:sapphire laser that produces sub-50-fs pulses

An external cavity coupled to a dispersion-compensated, self-mode-locked Ti:sapphire laser is shown to maintain cw mode locking to produce pulses as short as 47 fs. The same cavity arrangement is also shown to generate transform-limited pulses of 2-ps duration in the regime of linear external cavity mode locking.

Pulse evolution dynamics of a femtosecond passively mode-locked Ti:sapphire laser

The pulse-formation process in a femtosecond passively mode-locked Ti:sapphire laser with a saturable absorber is investigated. The time to reach the steady state is 200 micros. The formation time dependence on the dye concentration and the coincidence of the steady-state pulse width with the self-mode-locked state without a saturable absorber indicate that the function of the saturable absorber is mainly to induce the initial modulation and to shorten the pulse-formation time.

External frequency conversion of cw mode-locked Ti:Al(2)O(3) laser radiation

Efficient frequency conversion of cw mode-locked Ti:A1(2)O(3) laser radiation using lithium triborate, beta-barium borate, and lithium iodate crystals as the nonlinear material is demonstrated. Second-, third-, and fourth harmonic generation results in tunable blue and ultraviolet radiation down to 205 nm with transform-limited pulses and pulse lengths below 1 ps. Maximum average powers (repetition rate 82 MHz) of 700 mW at 400 nm, 120 mW at 272 nm, and 10 mW at 210 nm were obtained. The effects of group-velocity dispersion have to be taken into account to optimize the different frequency-conversion processes.

Theory of passive additive-pulse mode locking

The laser configuration of newly developed additive-pulse mode locking, also known as coupled-cavity mode locking, can be viewed as an intracavity interferometer. By solving the equation of motion of the two coupled cavities, a mathematical description of the self-starting mechanism is obtained. With this method, the transient pulse evolution of an initial seed pulse can be calculated and thereby optimized. The structure of the equation of motion suggests new single-cavity configurations of additive-pulse mode locking, and the same method of analysis can be applied to them.

Actively mode-locked Ti:sapphire laser producing transform-limited pulses of 150-fs duration

We report on the generation of transform-limited pulses of 150-fs duration from an actively mode-locked Ti:sapphire laser. The laser produced subpicosecond pulses over the range 780-860 nm, with a maximum average output power of 600 mW. The output spot was in the form of a near-TEM(00) spot and demonstrated longterm pulse stability.

Self-starting of an additive-pulse mode-locked color-center laser

Self-starting of additive-pulse mode-locking (APM) behavior has been observed in a NaCl:OH color-center APM laser over the wavelength range of 1.52-1.60 microm. Pulses as short as 160 fs have been produced at a wavelength of 1.55 microm in a stable pulse train. High-power levels in the fiber are required for the mode locking to self-start. The large fiber power makes it difficult to stabilize the cavity length by conventional methods: The feedback signal must now be derived from the second harmonic of the laser output. The self-starting APM laser exhibits less noise than the synchronously pumped APM laser because of the lack of pulse walk-off effects that are characteristic of the synchronously pumped APM laser.

50-fs pulse generation directly from a colliding-pulse mode-locked Ti:sapphire laser using an antiresonant ring mirror

50-fs pulses were directly generated from a colliding-pulse mode-locked Ti:sapphire laser. To achieve the collidingpulse mode locking, a miniature antiresonant ring containing an organic saturable dye jet was employed as the end mirror for the linear cavity laser. Based on measured dispersion of intracavity elements, a prism pair was implemented to control the cavity dispersion. The generated pulses have no linear chirp but do exhibit parabolic instantaneous frequency owing to third-order dispersion introduced by the prism pair.

Resonant frequency doubling of a self-starting, coupled-cavity, mode-locked Ti:A12O3 laser

We report the efficient frequency doubling of a self-starting, coupled-cavity, mode-locked Ti:sapphire laser (Ti:A1(2)O(3)). The laser produced pulses of 2.5-3.4 ps at a 122-MHz repetition rate that were tunable from 740 to 820 nm. These pulses were frequency doubled in an external ring enhancement cavity. Using a l-mm-long, Brewstercut LiIO(3) crystal, we obtained conversion efficiencies of as much as 34% in the form of picosecond pulses tunable from 370 to 410 nm. The maximum generated power in the blue was 48 mW at 384 nm.

Generation of 50-fsec pulses from a pulse-compressed, cw, passively mode-locked Ti:sapphire laser

Stable pulses of less than 150 fsec are generated directly from a tunable cw passively mode-locked Ti:sapphire laser, through a balance of self-phase modulation in the Ti:sapphire rod and negative group-velocity dispersion produced by a prism pair. After external fiber compression, 50-fsec pulses are obtained at approximately 750 nm.

Characteristics of an actively mode-locked 2-psec Ti:sapphire laser operating in the 1-microm wavelength regime

We examine the performance of an actively mode-locked Ti:sapphire laser operating in the 1-microm wavelength regime. Pulse durations of 1.7 psec are produced with an average output power of 400 mW. With the use of external dispersion compensation this pulse width has been further reduced to 850 fsec.

60-fsec pulse generation from a self-mode-locked Ti:sapphire laser

Pulses having durations as short as 60 fsec have been directly generated by a self-mode-locked, dispersion-compensated Ti:sapphire laser. By using an extracavity fiber-prism pulse compressor, pulse durations as short as 45 fsec have been obtained.

Starting dynamics of additive-pulse mode locking in the Ti:A1(2)O(3) laser

The starting dynamics of the additive-pulse mode-locked Ti:AI(2)O(3) laser are investigated. Mode locking develops from mode beating with pulse formation times of several hundred microseconds. A simple model based on additivepulse mode-locking theory is developed that describes self-starting and pulse evolution.

Subpicosecond pulse generation from a Nd:glass laser using a nonlinear external cavity

An actively mode-locked, continuous-wave Nd:glass laser pumped by a krypton laser at 0.8 microm has been coupled to a nonlinear external resonator. The 20-psec pulses produced by active mode locking are shortened to less than 1 psec with the nonlinear external cavity feedback. Subpicosecond pulse generation has been achieved at a pump power as low as 500 mW.

Passive mode locking of a cw Nd:YLF laser with a nonlinear external coupled cavity

Using an optical fiber as the nonlinear medium in an external cavity, we demonstrated passive mode locking of a cw Nd:YLF laser at a 1.053-microm wavelength. Nearly transform-limited pulses as short as 3.7 psec were obtained at a repetition rate of 76 MHz directly from the laser output without further compression. The average output power ranged from 1 to 7 W.

Self-starting additive-pulse mode locking of a Nd:YAG laser

We report additive-pulse mode locking of lamp-pumped Nd:YAG lasers at both 1.06 and 1.32 microm. Under completely self-starting conditions, stable cw mode-locked trains of 6-psec pulses have been achieved at an average output power of 2.4 W.

Self-starting additive-pulse mode-locked diode-pumped Nd:YAG laser

A diode-pumped Nd:YAG laser is demonstrated by using self-starting additive-pulse mode locking with a nonlinear external cavity. Pulse durations of 1.7 psec are generated at an average output power of 25 mW without the need for active amplitude or phase modulation. Design and scaling issues for this technology are discussed.

Ti:sapphire laser pumped by a frequency-doubled diode-pumped Nd:YLF laser

We report on the operation of a tunable all-solid-state (holosteric) laser system consisting of a tunable Ti:sapphire laser pumped by a frequency-doubled diode-laser-pumped Nd:YLF laser. With a 1-W pump diode, the Nd:YLF laser has been frequency-modulation mode locked and Q switched at 1.047 microm. This produces a pulse envelope of 75-nsec duration with 45 microJ of energy in 21-psec pulses at a 360-MHz repetition rate. This output was frequency doubled in 90 degrees phase-matched MgO:LiNbO(3) with a 47% energy conversion efficiency. The Ti:sapphire cavity was a three-mirror astigmatically compensated arrangement.The threshold absorbed pump energy was 3.9 microJ, with an output energy of 1.3 microJ at 10.8-microJ absorbed pump power.The tuning range was 746-838 nm and was limited by the mirror reflectivities.

Mode locking of a continuous-wave titanium-doped sapphire laser using a linear external cavity

The mode locking of a Ti:Al(2)O(3) laser with a moving extracavity mirror is described. With no active mode-locking element and with no nonlinear element in the external cavity, pulses of less than 40 psec have been directly generated from a cw laser. A possible mechanism for this novel mode-locking technique is discussed.

Femtosecond passively mode-locked Ti:Al(2)O(3) laser with a nonlinear external cavity

Ultrashort pulses are generated in a Ti:Al(2)O(3) laser by using a coupled nonlinear external cavity. The external cavity uses self-phase modulation in an optical fiber to achieve passive mode locking without the need for synchronous pumping or acousto-optic modulation. A stable train of chirped 1.4-psec pulses is generated. After dispersive compensation, pulses as short as 200 fsec are obtained.