Ultrashort Laguerre-Gaussian pulses with angular and group velocity dispersion compensation

Abstract

Coherent optical vortices are generated from ultrashort 6.4 fs pulses. Our results demonstrate angular dispersion compensation of ultrashort 6.4 fs Laguerre-Gaussian (LG) pulses as well as what is believed to be the first direct autocorrelation measurement of 80 fs LG amplified pulses. A reflective-mirror-based 4f-compressor is proposed to compensate the angular and group velocity dispersion of the ultrashort LG pulses.

Ultrashort optical-vortex pulse generation in few-cycle regime

“…The programmable hologram by LC-SLM, although allowing us to generate the optical vortices with almost any topological charge, brings about angular dispersion owing the diffraction effect. While the dispersion can be compensated for by using an additional diffraction optics [15], like a compensation of the angular dispersion, this compensation procedure is complicated as well as inherently imperfect; while, in the-ory, a perfect conversion is possible in a 4-f configuration [16], its throughput is quite limited (∼1%). The optical-vortex conversion using a uniaxial crystal, though enabling to generate the ultrabroadband intense pulses, is constrained by the conservation law of the total angular momentum (quantum number) j = + s, where and s denote topological charge associated with OAM and index of spin angular momentum (SAM), respectively.…”

Generation of intense femtosecond optical vortex pulses with blazed-phase grating in chirped-pulse amplification system of Ti:sapphire laser

“…1. The 4f setup is composed of a concave mirror C1, flat mirrors, and an LC-SLM (Hamamatsu Photonics X10468-01, 600 × 792 pixels) as The input beam is first converted into the OV by a forklike blazed-phase grating [15,26] in the upper part of the LC-SLM and then Fourier transformed using concave mirror C1 with a curvature of 1 m. Flat mirror M1 was placed at the focal plane of C1 and an aperture was set in front of M1 to selectively transmit the first-order diffraction light. The beam was then reflected back to the blazed-phase grating without a forklike pattern in the lower part of the LC-SLM to compensate the angular dispersion caused by the upper part.…”

“…Note that the incident beam to the 4f system was magnified in advance to ~3 mm at the 1/e 2 level to prevent damage to the LC-SLM. The phase describing the blazed grating with a spiral phase modulation, Φ, which was projected onto the xy plane of the LC-SLM, can be written as [15,26] where mod(a, b) = a − b Int(a/b) is the modulus function, Λ = (DS)/600 is the period of the grating, D = 10 mm is the width of the grating, S is the number of phase steps in a period, and 600 is the number of pixels. The Cartesian coordinates (x, y) on the LC-SLM are transformed to cylindrical coordinates (r = x 2 + y 2 , φ = arctan(y/x)).…”

“…Many studies have been carried out on monochromatic OVs, which have been widely used in the optical manipulation of molecules and nanoparticles [8][9][10]. More recently, scientists have been attempting to generate multichromatic OVs with high energy and ultrashort temporal profiles [11][12][13][14][15][16][17]. Such an OV pulse exhibits a high peak power, which is the key to inducing nonlinear phenomena such as filamentation [18], supercontinuum [19], and high-harmonic generation [20,21].…”

“…prism [27,28], 2f-2f [14], and 4f configurations [13,15] or space-variant waveplates [11,12]. In particular, the combination of achromatic methods and laser amplifiers opens new possibilities for the generation of OVs with not only an ultrashort temporal profile but also a fairly high output energy [11,12].…”