LUHS - LE-0700 "Green" SHG with Diode pumped Nd:YAG Laser

Topics:

  • Interaction of Light and Matter

  • Crystal Optics

  • Non-linear Optics

  • Second Harmonic Generation

  • Phase Matching Condition

  • Nd:YAG Laser

  • KTP Crystal

  • High Order Transverse Modes

  • BFT Green Line tuning

LE-0700 Green SHG with Diode pumped Nd:YAG Laser with hemi-spherical cavityA. LE-0700 "Green" SHG with Diode pumped Nd:YAG Laser with a hemi-spherical cavity

LE-0700 Green SHG with Diode pumped Nd:YAG Laser with concentric cavity and birefringent tunerB. LE-0700 "Green" SHG with Diode pumped Nd:YAG Laser with a concentric cavity with Birefringent tuner

Lasers which emit light in the short wavelength spectral range are expensive and not sufficiently reliable for many applications. A more economically way to generate such radiation is achieved by frequency doubling. Especially the generation of green laser radiation is an important requirement of the lithographic industry. At present the argon ion laser is being displaced more and more by frequency doubled diode pumped Nd:YAG lasers which deliver tens of watt in TEMoo and are the first choice for pumping the Titanium Sapphire which is of high importance and frequently used in research labs. In bio-photonics the green radiation serves as "optical tweezers" and the analysis of living cells. The principles of the generation of frequency doubled light will be explained and simultaneously the possibilities of non linear optics learnt in this experiment. The understanding of non linear optical effects is very important for laser technology, since the processes of generation of short pulses are also based on non linear effects. Within the experiment the phase matching condition will be presented and analyzed. The efficiency of frequency doubling will be determined and hints for an optimized conversion rate will be evaluated in the experiment. For the first time the frequency doubling can be followed up in an impressive manner by a practical experiment. The fundamental wave is generated by a diode laser (LD) pumped Nd:YAG (D) laser with an open resonator structure. The non-linear crystal (FD) is placed simply into the resonator and suddenly green light appears. Furthermore also the mode structure of the Nd:YAG laser becomes visible and shows a great variety of transverse modes. By introducing an adjustable iris (IS) into the cavity the number and kind of modes can be controlled and reduced down to TEM00.Nd:YAG laser oscillating on 1330 nm frquency doubled to 665 nm When using the "Red 660 nm" option the Nd:YAG laser is operated at 1.3 µm and a special cut KTP crystal allows the frequency doubling into the red part of the spectrum.
A birefringent tuner (Fig. B.) inside the cavity selects different lines of the fundamental wave resulting in frequency doubled lines in the range of 526 to 539 nm.

Principle of intra-cavity frequency doubling with a Nd:YAG laser A. Principle of intra-cavity second harmonic generation

One side of the Nd:YAG crystal is coated and forms the first mirror (M1) for the laser cavity. The second mirror (M2) is a curved mirror resulting in a hemispherical cavity. The Nd:YAG crystal is pumped by the radiation of 808 nm emitted from the laser diode. The divergent radiation is collimated (C) to an almost parallel beam and afterwards focused by the lens (L) in such a way that the focus lies within the Nd:YAG crystal. The KTP crystal is inserted into the cavity close to the Nd:YAG crystal where the beam waist is at smallest and thus the intensity of the fundamental radiation (1064 nm) at highest for efficient second harmonic generation (SHG). A filter is used to suppress the residual fundamental and pump radiation and to transmit the “green” SHG only.
Due to the high gain and the cavity design a lot of transverse modes of the fundamental wave exist which become visible due to the SHG process. By means of an adjustable iris (Fig. C) which is used inside the cavity close to the spherical mirror the manifold of the these modes can be controlled down to single transverse mode TEM00. However, the iris can also be used to set and study controlled higher transverse modes.

Principle of intra-cavity frequency doubling with a Nd:YAG laser B. Principle of second harmonic generation with KTP crystal

Principle of second harmonic generation with intra-cavity iris diaphragm to control transverse modes C. Principle of second harmonic generation with intra-cavity iris diaphragm to control transverse modes

Tuning different “green” lines from 526 up to 539 nm with birefringent tuner (PFT Plate) D. Tuning different “green” lines from 526 up to 539 nm with birefringent tuner (PFT Plate)

This experiment uses a birefringent tuner (BFT) to select one of the manifold of lines of the Nd:YAG laser around 1064 nm (see ) resulting in the same number of frequency doubled lines from 526 to 539 nm. The BFT is placed under the Brewster angle along with the KTP crystal inside the cavity. The change of the color is not sufficient to distinguish the lines, thus the use of a spectrometer is recommended.
LE-0700 "Green" SHG with Diode pumped Nd:YAG Laser, consisting of:
Item Code Qty. Description
1 CA-0060 1 Infrared display card 0.8 -1.4 µm
2 CA-0080 1 Optics cleaning set
3 CA-0450 3 BNC connection cable 1 m
4 DC-0040 1 Diode laser controller MK1
5 DC-0120 1 Si-PIN Photodetector, BPX61
6 MM-0020 3 Mounting plate C25 on carrier MG20
7 MM-0060 1 Filter plate holder on MG20
8 MM-0090 1 XY adjuster on MG20
9 MM-0100 1 Target Cross in C25 Mount
10 MM-0110 1 Translucent screen on carrier MG20
11 MM-0462 1 Kinematic mirror mount M16, right
12 MP-0150 1 Optical Bench MG-65, 500 mm
13 OC-0005 1 Biconcave lens f=-5 mm, C25 mount
14 OC-0060 1 Biconvex lens f=60 mm in C25 mount
15 OC-0170 1 Collimator 808 nm in C25 mount
16 OC-0400 1 Adjustable iris mounted in C25
17 OC-0939 1 Filter BG39, 50 x 50 x 3 mm
18 OC-0950 1 Filter RG1000 50x50x3 mm
19 OC-1070 1 Laser mirror M16, ROC 100 mm, HR @ 1064 nm
20 OM-0052 1 Cylindrical Beam Expander 3x
21 OM-0624 1 Nd:YAG rod in 2 axes kinematic mount
22 OM-0650 1 KTP crystal SHG 532 nm, 5 axes mount on carrier MG20
23 OM-L520 1 Diode laser module 808 nm 1W
24 UM-LE06 1 Manual for Nd:YAG Laser
Required Option (order separately)
25 CA-0200 1 Oscilloscope 100 MHz digital, two channel
Option (order separately)
26 CA-0270 1 Fiber coupled spectrometer 200 - 1200 nm, USB
27 OM-0580 1 Birefringent Tuner
Available Downloads
Media Type Title File Size [MBytes] Action
PDF  Manual LE-0600 Diode pumped Nd:YAG Laser
 Version:  2022		 7.08 MB Download
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